Thirty-Year Trends in Sleep Disorders and Cardiovascular Disease Risk

Abstract

The aim of the study was to examine the prevalence and trends of sleep disorders and to assess the impact of sleep disorders on the risk of cardiovascular disease in the population aged 25–64 years. Surveys of representative samples of the population aged 25–64 in Novosibirsk were conducted in 1988–2018.2650 men and 3113 women were studied. The risk of developing arterial hypertension (AH) during the first 5 years of follow-up was 5.4 times higher in men and 4.35 times higher in women with sleep disorders than in those without. Men with sleep disorders had a 2.4 times higher risk of MI than those without. The risk of stroke was 3 times greater in men and 1.9 times greater in women with sleep disorders than without. Sleep disorders are a risk factor for MI only in men; for AH and stroke - in both men and women.

1. Introduction

The growing interest in sleep disorders is due to several reasons. Insomnia is the most common sleep disorder, affecting an estimated 30% of the world’s adult population on a regular basis; 10% of people suffer from chronic insomnia [1, 2, 3]. Sleep disorders can lead to accidents and human error [1]. They can double the risk of fatal accidents [2, 3, 4]. The rapid emergence of “24/7” communities, i.e., 24 hours a day, 7 days a week, with attendance at round-the-clock events and increased use of television, Internet, and cell phones at night, means that adequate, uninterrupted nighttime sleep is becoming a rarity. Sleep problems are only getting worse every year. The research findings suggest that nighttime sleep duration has decreased over the past 30 years [5]. Complaints about sleep problems have increased significantly over the same period, and short sleep (<6 hours/night) has become increasingly common among full-time workers [6]. There is likely to be an increase in the proportion of workers with circadian rhythm disorders who are in demand to serve the “24/7” communities. Similarly, as the proportion of the world’s population that is elderly and the prevalence of obesity increase, sleep disorders will become more prevalent in the population and will increase in both low- and high-income countries [7]. Sleep plays an important role in maintaining good health. Studies conducted over the past decade have confirmed that sleep disorders have a powerful effect on the risk of infectious diseases, the onset and progression of a number of major medical conditions, including cardiovascular disease and cancer, and the incidence of depression [8, 9]. For optimal health and well-being, it is recommended that adults between the ages of 18 and 60 get at least 7 hours of sleep each night [10]. Sleep of <7 hours per day is associated with an increased risk of obesity, diabetes mellitus, hypertension, coronary heart disease, stroke, frequent mental disorders, and mortality from all causes [10, 11, 12, 13]. According to the results of a national survey, 25% of adults in the United States self-report that they do not get the recommended amount of sleep. There is also evidence that in many modern societies, there has been a decrease in the amount of sleep per night [14]. It is now known that the amount of sleep Americans get is on the decline, and the percentage of men and women who have slept less than 6 hours has increased significantly over the past 2 decades. In 1942, Americans slept an average of 7.9 hours per day, compared to 6.8 hours in 2013, which is 13% less [15]. Insufficient sleep impairs cognitive performance, which can increase the likelihood of road and other transportation accidents, occupational injuries, medical errors, and productivity losses that can affect society as a whole [16]. The relationship between sleep duration and adverse health outcomes is often described as a U-shaped curve, with minimal health risk associated with sleep duration of 7–8 hours, but the role of prolonged sleep >9 hours and its impact on health is less clear [10, 17]. The American Academy of Sleep Medicine (AASM) and the Sleep Research Society (SRS) concluded that “it is unclear whether sleeping more than 9 hours per day is associated with health risks” [18].

In Russia, about 45% of adults suffer from sleep disorders. Nearly 20% need serious sleep treatment [19]. In both physiological and pathological conditions, sleep is the most important modulator of the cardiovascular system. Sleep has a significant effect on the autonomic nervous system, hemodynamics, cardiovascular function, endothelial function, and the coagulation system. Epidemiologic and pathophysiologic studies have shown that sleep problems can be a contributor to cardiovascular disease (CVD) [20]. Robillard R. and co-authors found that sleep deprivation contributes to an increase in both SBP (systolic blood pressure) and DBP (diastolic blood pressure) in normotensive older people aged 60–69 years. The authors concluded that sleep deprivation leads to a change in blood pressure regulation mechanisms and may increase the risk of hypertension in healthy normotensive individuals [21]. In addition, daytime sleepiness has long been associated with high SBP and DBP and the development of hypertension 5 years later [22]. The high prevalence of hypertension in the elderly may be influenced by both insufficient and excessive sleep [23]. It is important to note that sleep deprivation in adolescents leads to an increase in heart rate, SBP and, to a lesser extent, DBP [24]. This confirms that changes in the sleep process - daytime sleepiness, and lack of nighttime sleep - lead to developing hypertension [25]. However, there are other data. Sleep disorders were not found to increase the risk of hypertension in a study conducted by Vozoris N.T. in 2014 [26]. Sleep disorders can be manifested by an imbalance of the autonomic nervous system in response to chronic stress, often accompanied by an increase in metabolic rate, an increase in heart rate, a decrease in heart rate variability, and an increase in cortisol secretion. Thus, dysregulation of the autonomic nervous system and the hypothalamic-pituitary axis contribute to the development of a mechanism linking sleep disorders and cardiovascular disease [27, 28]. The causal relationship between sleep disorders and cardiovascular diseases is also experimentally confirmed, for example, sleep deprivation leads to an increase in blood pressure and the level of inflammatory mediators, as well as to a violation of carbohydrate metabolism and increased atherogenesis, and subsequently to cardiovascular diseases. In addition, sleep fragmentation can have a negative impact on blood flow to the brain and lead to cerebral circulation problems [29]. Women are more likely than men to complain about the quality of their sleep, especially as they age. 81% of women complain about insomnia, while 78% of men are likely to complain about sleep problems. Women are more likely to wake up early (50%) than men (41%) and have more difficulty falling asleep - 33 and 31% respectively [30].

Taking into account the above facts, the purpose of our study was to investigate the prevalence and thirty-year trends of sleep disorders, as well as to assess the impact of sleep duration and sleep disorders on the risk of cardiovascular diseases in the healthy population of Novosibirsk, Western Siberia, Russian Federation.

2. Materials and methods

The study results were obtained based on a survey of the able-bodied population of the Oktyabrsky district of Novosibirsk. The study included materials from 5 screening studies of representative samples of the population aged 25–64 years (budget topic Reg. No. FWNR-2024-0002). During the screening II in 1988–1989 1435 individuals were examined: 725 men, mean age 43.4 ± 0.4 years, response - 71.3% and 710 women, mean age 44.8 ± 0.4 years, response - 72%. During screening III in 1994–1995, 1038 individuals were examined: 647 men, mean age − 44.3 ± 0.4 years, response - 82.1%; 391 women, mean age - 45.4 + −0.4 years, response - 72.5%. During the screening IV in 2003–2005 1650 individuals were examined: 576 men, mean age - 54.23 ± 0.2 years, response - 61%; 1074 women, mean age - 54.27 + 0.2 years, response - 72%. During the screening V in 2013–2016, 975 individuals were examined: 427 men, mean age 34 ± 0.4 years, response - 71%; 548 women, mean age 35 ± 0.4 years, response - 72%. During the screening VI in 2016–2018, 665 individuals were examined: 275 men, mean age 49 ± 0.4 years, response - 72%; 390 women, mean age 45 ± 0.4 years, response - 75%.

The general examination in 1988–1989, 1994–1995, 2003–2005, 2013–2016, 2016–2018 was carried out according to the standard methods of the WHO program “MONICA-psychosocial (MOPSY)” [31]. Sleep disorders were assessed using the WHO “MONICA-psychosocial (MOPSY)” scales [31]. The respondents were asked the question: “How can you rate the quality of your sleep?” The range of responses included the following options: “very good”, “good”, “satisfactory”, “bad”, “very bad”. There was another question: “How many hours a day do you usually sleep?” The range of responses included the following options: “5 hours and less”, “6 hours”, “7 hours”, “8 hours”, “9 hours”, “10 hours and more”. The analyzed level of the risk factor was taken as its value in the original study. The contribution of time dynamics was not taken into account. The methods were strictly standardized and met the requirements of the WHO “MONICA-psychosocial” protocol [31].

Processing of the findings under the WHO MONICA psychosocial program was carried out at the MONICA Information Collection Center in Helsinki, Finland. Quality control was performed at MONICA Quality Control Centers in Dundee (Scotland), Prague (Czech Republic), and Budapest (Hungary). The results presented were considered satisfactory [31].

All women and men with identified cardiovascular pathology (coronary heart disease, cerebral vascular disease, hypertension, myocardial infarction, diabetes mellitus) occurring before or during the screening period were excluded from the observation cohort.

The screening III materials were used to assess the effect of sleep disorders on the risk of developing CVD (hypertension, myocardial infarction, and stroke). Included in the analysis were 384 women and 190 men at the baseline age of 25 to 64 years. The period of the prospective observation of the participants lasted from the 1st of January 1996 to the 31st of December 2012.

The subject of the study of the risk of myocardial infarction (MI) in relation to sleep duration was an observational cohort (the screening IV) consisting of men and women initially aged 45–64 years. Included in the analysis were 428 men and 798 women with a baseline age of 45 to 64 years (the screening IV). The period of prospective observation of the participants was as follows: from January 1, 2006 to December 31, 2019.

The following “endpoints” were identified in the study: first-ever cases of arterial hypertension (AH) recorded during the follow-up period. Sources used to identify cases of hypertension included: annual examination of individuals in the population cohort, medical histories, inpatient discharge reports, district clinics, death certificates, interviews with relatives, and pathoanatomical and forensic reports. During the annual follow-up, a standardized measurement of blood pressure (BP) was performed with a mercury sphygmomanometer on the right hand (the first phase of Korotkov tones was recorded as SBP, the fifth phase as DBP), the average of two measurements was included in the analysis. Hypertension was defined as SBP of 140 mmHg or higher and/or DBP of 90 mmHg or higher in subjects who were not receiving antihypertensive therapy at the time of the examination. Men with normal blood pressure were also included in the hypertensive group if they were taking antihypertensive medication during the examination period or had stopped taking it less than 2 weeks before the examination (WHO, 1993).

First-time cases of myocardial infarction (MI) and stroke. Registration of all cases of MI was based on the WHO Acute Myocardial Infarction Registry Program; first-time cases of stroke were recorded during the follow-up period. Sources used to identify stroke cases included: annual examination of individuals in the population cohort, medical histories, inpatient discharge reports, district clinics, death certificates, interviews with relatives, pathoanatomical and forensic reports.

During cohort follow-up (the screening III), 229 cases of first-time hypertension were detected in women and 46 in men; 15 cases of first-time hypertension in women and 30 in men; and 35 cases of first-time stroke in women and 22 in men. During cohort follow-up (the screening IV), 44 new cases of MI were detected in men and 37 in women.

SPSS software package version 20 was used for statistical analysis [15]. The Pearson chi-squared criterion was used to test the statistical significance of the differences between the groups [32]. The risk of hypertension, MI, and stroke was assessed using a single-factor Cox proportional regression model [32]. The probability was assumed to be at a significance level of p < 0.05.

3. Results

The level of sleep disorders (“bad”, “very bad” sleep) in men of 25–34 years of age in 1988–1989 was 5.4%; in 1994–1995-3.6%; in 2013–2016 - 4.3% (p < 0.01). In women, the level of sleep disorders accounted for 13.7% in 1988–1989, 7.9% in 1994–1995; in 2013–2016-5.7% (p < 0.001). In men aged 35 to 44 years, the levels of sleep disorders were 9.5 percent from 1988 to 1989, 9.3 percent in 1994 to 1995, 4.2 percent in 2013 to 2016, and 11 percent in 2016 to 2018 (p < 0.05). The level of sleep disorders in women was 17.9% in 1988–1989, 20% in 1994–1995, 14.2% in 2013–2016, and 10.3% in 2016–2018 (p < 0.001). In the 45–54 age group of men, the level of sleep disorders was 11% in 1988–1989, 9.8% in 1994–1995, 12.5% in 2003–2005, and 4.9% in 2016–2018 (p < 0.05). In women aged 45–54 years, the level of sleep disorders was 24% in 1988–1989, 15.2% in 1994–1995, 17.9% in 2003–2005, and 22.8% in 2016–2018 (p < 0.001). In the older age group 55–64 years, the level of sleep disorders in men aged 55–64 years was - 20.8% in 1988–1989, − 12.1% in 1994–1995, − 11.8% in 2003–2005, and - 19.7% in 2015–2018 (p < 0.001). In women aged 55–64 years, the level of sleep disorders was 35.8% in 1988–1989, 27% in 1994–1995, 21.8% in 2003–2005, and 24.9% in 2016–2018 (p < 0.001). In the age group 25–64 years, the level of sleep disorders among men in 1988–1989 was 11%, in 1994-1995-8.6%; in the age group 45–64 years in 2003–2005 - 12.2%; in the age group 25–44 years in 2013–2016-4.2%; in the age group 35–64 years in 2016–2018-2113.1% (p < 0.001); in women in the age group 25–64 years in 1988-1989-21.8%, in 1994–1995 - 16.6%, in the age group 45–64 years in 2003–2005-2019.7%; in the age group 25–44 years in 2013–2016-2110.8%; in the age group 35–64 years in 2016–2018-2020.5% (p < 0.001). (see Table 1).

Question/Attitude		25–34				35–44				45–54				55–64				25–64*
		Men		Women		Men		Women		Men		Women		Men		Women		Men		Women
		N	%	N	%	N	%	N	%	N	%	N	%	N	%	N	%	N	%	N	%
How can you rate the quality of your sleep?
1. Very good	1988–1989	35	17.2	10	5.5	16	8	8	3.9	10	5.8	6	3.3	8	5.4	4	2.9	69	9.5	28	3.9
2. Good		101	49.5	75	41	91	45.7	67	32.4	59	34.1	37	20.2	42	28.2	14	10.2	293	40.5	193	27.2
3. Satisfactory		57	27.9	73	39.9	73	36.7	95	45.9	85	49.1	96	52.5	68	45.6	70	51.1	283	39	334	47.1
4. Bad		10	4.9	23	12.6	17	8.5	31	15	15	8.7	33	18	30	20.1	46	33.6	72	9.9	133	18.7
5. Very bad		1	0.5	2	1.1	2	1	6	2.9	4	2.3	11	6	1	0.7	3	2.2	8	1.1	22	3.1
Total		204	100	183	100	199	100	207	100	173	100	183	100	149	100	137	100	725	100	710	100
		χ2 = 24.08 υ = 4 P = 0.001				χ2 = 15.1 υ = 4 P = 0.01				χ2 = 16.4 υ = 4 P = 0.001				χ2 = 19.2 υ = 4 P = 0.001				χ2 = 66.6 υ = 4 P = 0.001
1. Very good	1994–1995	9	5.4	8	6.3	11	6.4	5	3.2	8	5.6	3	6.5	8	4.8	1	1.6	36	5.6	17	4.3
2. Good		97	58.1	54	42.5	72	41.9	47	30.3	55	38.5	11	23.9	75	45.5	9	14.3	299	46.2	121	31
3. Satisfactory		55	32.9	55	43.3	73	42.4	72	46.5	66	46.2	25	54.3	62	37.6	36	57.1	256	39.6	188	48.1
4. Bad		5	3	7	5.5	14	8.1	29	18.7	13	9.1	6	13.0	17	10.3	14	22.2	49	7.6	56	14.3
5. Very bad		1	0.6	3	2.4	2	1.2	2	1.3	1	0.7	1	2.2	3	1.8	3	4.8	7	1	9	2.3
Total		167	100	127	100	172	100	155	100	143	100	46	100	165	100	63	100	647	100	391	100
		χ2 = 8.35 υ = 4 P > 0.05				χ2 = 11.89 υ = 4 P < 0.05				χ2 = 3.902 υ = 4 P > 0.05				χ2 = 23.577 υ = 4 P < 0.001				χ2 = 32.202 υ = 4 P = 0.001
1. Very good	2003–2005									10	3.3	23	4.2	10	3.7	11	2.1	20	3.5	34	3.2
2. Good										104	34.2	107	19.3	73	26.8	88	16.9	177	30.7	195	18.2
3. Satisfactory										152	50	325	58.7	157	57.7	308	59.2	309	53.6	633	58.9
4. Bad										37	12.2	94	17	29	10.7	108	20.8	66	11.5	202	18.8
5. Very bad										1	0.3	5	0.9	3	1.1	5	1	4	0.7	10	0.9
Total										304	100	554	100	272	100	520	100	576	100	1074	100
										χ2 = 22.62 υ = 4 P = 0.001				χ2 = 20.9 υ = 4 P = 0.001				χ2 = 5.72 υ = 4 P = 0.221
1. Very good	2013–2016	25	15.2	29	13.7	28	10.7	30	9.1									53	12.4	59	10.8
2. Good		78	47.6	105	49.5	126	48.3	137	41.4									205	48	243	44.3
3. Satisfactory		54	32.9	66	31.1	96	36.8	117	35.3									151	35.4	187	34.1
4. Bad		6	3.7	11	5.2	10	3.8	42	12.7									16	3.7	53	9.7
5. Very bad		1	0.6	1	0.5	1	0.4	5	1.5									2	0.5	6	1.1
Total		164	100	212	100	261	100	331	100									427	100	548	100
		χ2 = 0.836 υ = 4 P = 0.933				χ2 = 16.918 υ = 4 P = 0.002												χ2 = 14.425 υ = 4 P = 0.006
1. Very good	2016–2018					6	8.3	6	6.2	3	3.7	1	0.7	0	0	4	2.6	9	3.3	11	2.8
2. Good						32	44.4	43	44.3	35	43.2	45	32.1	35	28.7	33	21.6	102	37.1	121	31.1
3. Satisfactory						26	36.1	38	39.2	39	48.1	62	44.3	63	51.6	78	51	128	46.5	178	45.6
4. Bad						8	11.1	10	10.3	4	4.9	31	22.1	24	19.7	35	22.9	36	13.1	76	19.5
5. Very bad						0	0	0	0	0	0	1	0.7	0	0	3	2.0	0	0	4	1
Total						72	100	97	100	81	100	140	100	122	100	153	100	275	100	390	100
						χ2 = 0.396 υ = 3 P > 0.05				χ2 = 14.606 υ = 4 P < 0.01				χ2 = 7.304 υ = 4 P > 0.05				χ2 = 8.646 υ = 4 P > 0.05
Total		χ2 = 14.858 υ = 8 P < 0.01		χ2 = 24.715 υ = 8 P < 0.001		χ2 = 12.67 υ = 12 P < 0.05		χ2 = 21.177 υ = 12 P < 0.001		χ2 = 14.280 υ = 12 P < 0.05		χ2 = 40.155 υ = 12 P < 0.001		χ2 = 41.093 υ = 12 P < 0.001		χ2 = 22.01 υ = 12 P < 0.001		χ2 = 122.061 υ = 16 P < 0.001		χ2 = 230.626 υ = 16 P < 0.001

Table 1.

The prevalence of sleep disorders among the population aged 25–64 years from 1988 to 2018.

^*

2003–2005 - 45-64 y.o., 2013–2016 - 25-44 y.o., 2016–2018 - 35-64 y.o.

In the population aged 45–64 years, between 2003 and 2005 (the screening IV) and 2015–2018 (the screening VI), the number of people with 7 hours of sleep per night decreased from 44.9 to 31.9% (for men from 44.6–31% and for women from 45.1 to 32.4%); and with 8 hours of sleep per night - from 28.5 to 24.4% (for men from 27.8 to 23.2% and for women from 28.8 to 25.3%). The number of people sleeping less than 5 hours increased during the period from 2003 to 2005 to 2015–2018 from 4.9 to 9.9% (for men from 4.4 to 7.4% and for women from 5.1 to 11.6%); and 6 hours from 16.2 to 27.2% (for men from 17.2 to 31.5% in men and 15.7 to 24.2% in women). The number of people sleeping 9 hours per night increased from 3.7 to 5.4% (from 4.2 to 4.9% in men and from 3.4 to 5.8% in women) (p < 0.001) (see Table 2).

Hours slept	population screening IV 2003–2005		population screening VI 2015–2018		men screening IV 2003–2005		men screening VI 2015–2018		women screening IV 2003–2005		women screening VI 2015–2018
	n	%	n	%	n	%	n	%	n	%	n	%
5 hours	79	4.9	49	9.9	25	4.4	15	7.4	54	5.1	34	11.6
6 hours	263	16.2	135	27.2	97	17.2	64	31.5	166	15.7	71	24.2
7 hours	727	44.9	158	31.9	252	44.6	63	31	475	45.1	95	32.4
8 hours	461	28.5	121	24.4	157	27.8	47	23.2	304	28.8	74	25.3
9 hours	60	3.7	27	5.4	24	4.2	10	4.9	36	3.4	17	5.8
10 hours	29	1.8	6	1.2	10	1.8	4	2	19	1.8	2	0.7
Total	1619	100	496	100	565	100	203	100	1054	100	293	100
	χ2 = 61.285 df = 5 p < 0.001				χ2 = 25.306 df = 5 p < 0.001				χ2 = 38.99 df = 5 p < 0.001

Table 2.

Dynamics of hours slept per day for the population aged 45–64 from 2003 to 2005 to 2015–2018.

In 2003–2005 (the screening IV), in the population aged 55–64 years, sleep of less than 5 hours (5.5%), 7 hours (45.1%), 8 hours (29.4%), 9 hours (4.4%) and ≥ 10 hours (2.1%) was observed. On the contrary, in the group of people aged 45–54 years −18.9% (p < 0.01), a similar trend was observed in men (p > 0.05) and was significant in women (p < 0.05) (see Table 3). For the screening VI examination, there were no significant differences between sleep duration and age group. A comparative analysis between the two screenings showed that in the 45–54-year-old population group, 7-hour (44.7%), 8-hour (27.6%) and 10-hour (1.5%) sleep was more common at the screening IV, and 5-hour (9.5%), 6-hour (28.1) and 9-hour (5%) sleep at the screening VI (p < 0.001). In the 55–64-year-old group, 7-hour sleep (45.1%), 8-hour sleep (29.4%) and 10-hour sleep (2.1%) prevailed at the screening VI, whereas 5-hour sleep (10.2%), 6-hour sleep (26.5%) and 9-hour sleep (5.8%) prevailed at the screening VI (p < 0.001). In the 45–54-year-old men, sleep of less than 5 hours (9.9%), 6 hours (29.6%) and 9 hours (6.2%) prevailed at the screening VI, and 7 hours (44.3%) and 8 hours (27%) at the screening IV (p < 0.01). In the 55–64 age group, 7-hour (45%), 8-hour (28.6%), and 9-hour (5.2%) sleep predominated at the screening IV and 5-hour (5.7%), 6-hour (32.8%), and 10-hour (3.3%) sleep predominated at the screening VI (p < 0.001). In women in the 45–54 age group, 7-hour (44.9%) and 8-hour (27.9%) sleep was more common at the screening IV, and 5-hour (9.3%), 6-hour (27.1%) and 9-hour (4.3%) sleep was more common at the screening VI, as well as 10-hour (1.4%) sleep ($\chi$p < 0.05). In the group of women aged 55–64 years, 7-hour (45.2%), 8-hour (29.8%) and 10-hour (2.4%) were more common for the screening IV, 5-hour (13.7%), 6-hour (21.6%) and 9-hour (7.2%) sleep for the screening VI ($\chi$p < 0.001) (see Table 3).

Number of hours slept	Both sexes, screening IV, 2003–2005				Men, screening IV, 2003–2005				Women, screening IV, 2003–2005
	45–54 y.o.		55–64 y.o.		45–54 y.o.		55–64 y.o.		45–54 y.o.		55–64 y.o.
	n	%	n	%	n	%	n	%	n	%	n	%
5 hours	35	4.3	44	5.5	12	4.1	13	4.8	23	4.4	31	5.8
6 hours	155	18.9	108	13.5	57	19.3	40	14.9	98	18.7	68	12.8
7 hours	366	44.7	361	45.1	131	44.3	121	45	235	44.9	240	45.2
8 hours	226	27.6	235	29.4	80	27	77	28.6	146	27.9	158	29.8
9 hours	25	3.1	35	4.4	10	3.4	14	5.2	15	2.9	21	4
10 hours	12	1.5	17	2.1	6	2	4	1.5	6	1.1	13	2.4
total	819	100	800	100	296	100	269	100	523	100	531	100
	χ2 = 11.942 df = 5 p < 0.01				χ2 = 3.257 df = 5 p > 0.05				χ2 = 10.652 df = 5 p < 0.05
	Both sexes, screening VI, 2015–2018				Men, screening VI, 2015–2018				Women, screening VI, 2015–2018
5 hours	21	9.5	28	10.2	8	9.9	7	5.7	13	9.3	21	13.7
6 hours	62	28.1	73	26.5	24	29.6	40	32.8	38	27.1	33	21.6
7 hours	75	33.9	83	30.2	28	34.6	35	28.7	47	33.6	48	31.4
8 hours	50	22.6	71	25.8	16	19.8	31	25.4	34	24.3	40	26.1
9 hours	11	5	16	5.8	5	6.2	5	4.1	6	4.3	11	7.2
10 hours	2	0.9	4	1.5	0	0	4	3.3	2	1.4	0	0
total	221	100	275	100	81	100	122	100	140	100	153	100
	χ2 = 1.679 df = 5 p > 0.05				χ2 = 5.578 df = 5 p > 0.05				χ2 = 5.636 df = 5 p > 0.05

Table 3.

Distribution of number of sleep hours per day by age group in the population aged 45–64 (screening IV 2003–2005 and screening VI 2015–2018).

45–54 y.o., both sexes χ2 = 24.421 df = 5 p < 0.001; men χ2 = 12.876 df = 5 p < 0.01; women χ2 = 13.324 df = 5 p < 0.05

55–64 y.o., both sexes χ2 = 40.726 df = 5 p < 0.001; men χ2 = 20.73 df = 5 p < 0.001; women χ2 = 28.225 df = 5 p < 0.001

Table 4 shows self-rated sleep quality depending on the time spent sleeping. In 2003–2005, 40.9% of people with 8 hours of sleep considered their sleep to be “good” (p < 0.001): 38.8% of men (p < 0.001) and 42.6% of women (p < 0.001). In 2015–2018, people with 7 hours of sleep were more likely to say their sleep was “good” - 35.3% (p < 0.001), among men there was a trend toward 6 hours of sleep - 38.4% (p > 0.05), and among women, 7 hours of sleep - 37.3% (p < 0.01). In 2015–2018, people who slept 7 hours a day were more likely to rate their sleep as “bad” - 36.7% (p < 0.001), the trend for men is 39.3% (p > 0.05), and for women, the trend for 6 hours of sleep is 35.7% (p < 0.01) (see Table 4).

Number of hours slept	Both sexes, screening IV, 2003–2005						Men, screening IV, 2003–2005						Women, screening IV, 2003–2005
	good sleep		satisfactory sleep		bad sleep		good sleep		satisfactory sleep		bad sleep		good sleep		satisfactory sleep		bad sleep
	n	%	n	%	n	%	n	%	n	%	n	%	n	%	n	%	n	%
5 hours	16	3.3	45	3.8	46	13.3	5	2.2	16	3.9	13	14.9	11	4.2	29	3.7	33	12.7
6 hours	71	14.5	162	13.7	85	24.5	34	15.2	67	16.5	18	20.7	37	14	95	12.2	67	25.8
7 hours	163	33.3	622	52.6	120	34.6	80	35.7	210	51.7	30	34.5	83	31.3	412	53.1	90	34.6
8 hours	200	40.9	290	24.5	81	23.3	87	38.8	92	22.7	21	24.1	113	42.6	198	25.5	60	23.1
9 hours	27	5.5	41	3.5	12	3.5	11	4.9	12	3	5	5.7	16	6	29	3.7	7	2.7
10 hours	12	2.5	22	1.9	3	.9	7	3.1	9	2.2	0	0	5	1.9	13	1.7	3	1.2
	489	100	1182	100	347	100	224	100	406	100	87	100	265	100	776	100	260	100
	χ2 = 137.314 df = 10 p < 0.001						χ2 = 48.4 df = 10 p < 0.001						χ2 = 100.071 df = 10 p < 0.001
	Both sexes, screening VI, 2015–2018						Men, screening VI, 2015–2018						Women, screening VI, 2015–2018
Number of hours slept	good sleep		satisfactory sleep		bad sleep		good sleep		satisfactory sleep		bad sleep		good sleep		satisfactory sleep		bad sleep
	n	%	n	%	n	%	n	%	n	%	n	%	n	%	n	%	n	%
5 hours	7	4.5	23	9.5	19	19.4	1	1.4	10	9.8	4	14.3	6	7.2	13	9.3	15	21.4
6 hours	46	29.5	53	21.9	36	36.7	28	38.4	25	24.5	11	39.3	18	21.7	28	20	25	35.7
7 hours	55	35.3	84	34.7	19	19.4	24	32.9	32	31.4	7	25.0	31	37.3	52	37.1	12	17.1
8 hours	35	22.4	68	28.1	18	18.4	15	20.5	27	26.5	5	17.9	20	24.1	41	29.3	13	18.6
9 hours	11	7.1	12	5	4	4.1	4	5.5	6	5.9	0	0	7	8.4	6	4.3	4	5.7
10 hours	2	1.3	2	0.8	2	2	1	1.4	2	2	1	3.6	1	1.2	0	0	1	1.4
	156	100	242	100	98	100	73	100	102	100	28	100	83	100	140	100	70	100
	χ2 = 30.525 df = 10 p < 0.001						χ2 = 15.702 df = 10 p > 0.05						χ2 = 25.543 df = 10 p < 0.01

Table 4.

Distribution of hours slept per night according to self-rated sleep quality in the population aged 45–64.

5 years after the start of the study, a single-factor regression analysis of Cox showed that among men with sleep disorders, the risk of hypertension was higher HR = 5.4 (95% CI 2.5–10.8; p < 0.05) than in women HR =4.35 (95% CI 1.29–14.58; p < 0.05). After 10 years, the risk of hypertension did not differ between women HR = 2.68 (95% CI 1.3–7.15; p < 0.05) and men HR = 2.3 (95% CI 1.2–8.8; p < 0.05). After 16 years, only a tendency to reduce the risk of developing hypertension remained: HR = 1.2 in men (95% CI 0.19–3.59; p < 0.05) and HR = 1.05 in women (95% CI 0.73–1.48; p > 0.05) (see Table 5).

Sex	Age group	Male				Female
		p	HR	95% CI for HR		p	HR	95% CI for HR
				lower	upper			lower	upper
5 years	25–34	—	—	—	—	>0.05	2.17	0.22	20.92
	35–44	—	—	—	—	>0.05	4.05	0.18	90.75
	45–54	>0.05	2.2	0.7	4.2	>0.05	1.32	0.13	12.95
	55–64	>0.05	0.3	0.02	2.6	>0.05	4.52	0.52	38.92
	25–64	0.05	5.4	2.5	10.8	0.05	4.35	1.29	14.58
10 years	25–34	—	—	—	—	>0.05	0.33	0.22	3.25
	35–44	—	—	—	—	>0.05	6.44	0.8	51.82
	45–54	>0.05	2.1	0.01	3.9	>0.05	2.37	0.50	11.11
	55–64	>0.05	0.02	0.008	2.5	>0.05	1.13	0.09	13.26
	25–64	0.05	2.3	1.2	8.8	0.05	2.68	1.3	7.15
16 years	25–34	>0.05	1	0.08	1.4	>0.05	1.21	0.68	2.16
	35–44	>0.05	1.1	0.03	1.6	>0.05	0.66	0.34	1.26
	45–54	>0.05	2	0.9	4.7	>0.05	1.9	0.84	4.34
	55–64	>0.05	1.4	0.01	2.9	>0.05	4.47	0.27	71.8
	25–64	0.05	1.2	0.19	3.59	>0.05	1.05	0.73	1.48

Table 5.

Single factor cox regression analysis of sleep disorders and risk of hypertension in the 25–64-year-old population.

Multivariate Cox regression analysis including age and social characteristics (marital status, educational level, occupational status) in the model showed an increased risk of hypertension among people with sleep disorders in men HR = 3.1(95% CI 1.2–8.2, p < 0.01) than in women HR = 2.5(95% CI 1.3–4.8, p < 0.005). Moreover, the risk of hypertension in the group of widowed individuals with sleep disorders was higher in men than in women HR = 14.6 (95% CI 3–27, p < 0.01) compared to married HR = 5.6 (95% CI 2.6–11.8; p < 0.0001). We found an increased risk of hypertension only in women with sleep disorders and with a secondary education HR = 3.3 (95% CI 1.3–8.3; p < 0.008) or incomplete secondary - primary education HR = 10.3 (95% CI 4–26; p < 0.0001). No similar patterns have been found in men. In people aged 45–64 years, the risk of hypertension was 3.2 (95% CI 1.7–8.6; p < 0.05) times higher in men compared with the 25–34-year age group, and there were no reliable results for women (see Table 6).

Sex		Male				Female
Reference group	Risk group	p	HR	95% CI for HR		p	HR	95% CI for HR
				lower	upper			lower	upper
Good sleep	Bad sleep	0.01	3.1	1.2	8.2	0.005	2.5	1.3	4.8
Married	Never been married	0.9	1.1	0.1	9.1	0.5	1.3	0.5	3.3
	Divorced	0.1	2.5	0.8	7.7	0.2	1.9	0.6	5.39
	Widowed	0.01	14.6	3	27	0.0001	5.6	2.6	11.8
Higher education	n/higher or secondary vocational education	0.5	1.6	0.3	7.5	0.18	1.8	0.7	4.4
	Secondary education	0.8	1.2	0.2	6.9	0.008	3.3	1.3	8.3
	n/secondary - primary education	0.4	1.7	0.4	7.1	0.0001	10.3	4	26
Managers and engineers	Workers	0.4	2.4	0.2	16	0.9	0.9	0.4	1.9
25–34 y.o.	35–64 y.o.	0.05	3.2	1.7	8.6	0.9	1	0.01	2.1

Table 6.

Multivariate cox regression analysis of sleep disorders and risk of hypertension in the 25–64-year-old population 25–64 over 16-year period.

A single-factor Cox regression analysis showed that individuals with sleep disorders had a 2.4 (95%CI 1.1–5.3; p < 0.05) times increased risk of developing MI over a 16-year period compared to men without sleep disorders. Sleep disorders did not affect women’s risk of having an MI (see Table 7).

Sex		Male				Female
25–64 y.o.	CVD	p	HR	95% CI for HR		p	HR	95% CI for HR
				lower	upper			lower	upper
	Myocardial infarction	0.05	2.4	1.1	5.3	>0.05	1.05	0.3	3
	stroke	0.05	3	1.2	7.6	0.05	1.9	1.03	3.7

Table 7.

Single-factor cox regression analysis of sleep disorders and risk of CVD in the 25- to 64-year-old population.

In a single-factor Cox regression analysis over a 16-year period in individuals with sleep disorders, the risk of stroke was higher among men HR = 3 (95% CI 1.2–7.6; p < 0.05) than among women HR = 1.9 (95%CI 1.03–3.7; p < 0.05) (Table 7).

In the multivariate Cox regression model, we also did not obtain an effect of sleep disorders on the risk of developing MI, and stroke in women HR = 2.09 (95% CI 0.23–18.75; p > 0.05). In men, when social parameters were included in the model: marital status, education, occupational level, and age, the risk of developing MI decreased, and there was only a tendency to increase the risk by 1.08 (95% CI 0.4–4.7; p < 0.05) times. The marital status of the men with sleep disorders had a major impact on their risk of developing an MI. The risk of MI was 3 (95% CI 1.9–9; p < 0.0001) times higher in men who had never been married, HR = 4.3 (95% CI 2.1–8.9) in divorced men, and the highest risk was in widowed men HR = 7.5 (95% CI 2.5–22; p < 0.0001). No similar pattern has been found in the women. It was found that in the presence of sleep disorders, the risk of developing MI is higher in men aged 55–64 years HR = 6.4 (95%CI 2–21; P < 0.01) than in women in the same age group HR = 2.6 (95%CI 1.06–6.5; P < 0.05), compared with people aged 25–54 years without sleep disorders (see Table 8).

Sex		Male				Female
Reference group	Risk group	p	HR	95,0% CI for HR		p	HR	95,0% CI for HR
				lower	upper			lower	upper
Good sleep	Sleep Disorder	0.05	1.08	0.4	4.7	>0.05	2.09	0.23	18.75
Married	Never been married	0.05	3	1.9	9	>0.05	1.59	0.0001	2.47
	Divorced	0.0001	4.3	2.1	8.9	>0.05	8.88	0.0001	13.83
	Widowed	0.0001	7.5	2.5	22	>0.05	1.890	0.2	17.5
Higher education	n/higher or secondary vocational education	>0.05	0.9	0.3	2.5	>0.05	1.473	0.1	16.4
	Secondary education	>0.05	1.7	0.6	5.1	>0.05	1.367	0.08	21.8
	n/secondary - primary education	>0.05	1.3	0.5	3.5	>0.05	2.382	0.1	39.1
Managers and engineers	Workers	>0.05	5.8	0.6	48	>0.05	1.152	0.12	11.03
25–54 y.o.	55–64 y.o.	0.01	6.4	2	21	0.05	2.6	1.06	6.5

Table 8.

Multivariate cox regression analysis of sleep disorders and risk of MI in the 25–64-year-old population over 16-year period.

Multivariate Cox regression analysis including marital status, education level, occupational status, and age in the model showed that among people with sleep disorders, the risk of stroke is approximately the same for men HR = 2.8 (95% CI 1.1–7.1; P < 0.05) and women HR = 2.7 (95% CI 1.4–5.42; P < 0.01) (see Table 9).

Sex		Male				Female
Reference group	Risk group	p	HR	95,0% CI for HR		p	HR	95,0% CI for HR
				lower	upper			lower	upper
Good sleep	Sleep Disorder	0.05	2.8	1.1	7.1	0.01	2.7	1.4	5.42
Married	Never been married	>0.05	1.1	0.1	9.1	>0.05	0.7	0.2	2.44
	Divorced	>0.05	2.5	0.8	7.7	>0.05	0.9	0.2	3.8
	Widowed	0.01	1.9	1.2	3	>0.05	0.2	0.02	2.2
Higher education	n/higher or secondary vocational education	>0.05	1.8	0.4	7.9	>0.05	2.4	0.78	7.54
	Secondary education	>0.05	1.6	0.3	7.3	0.05	3.7	1.1	11.9
	n/secondary - primary education	0.01	5.3	1.4	19.1	0.05	4.2	1.25	14
Managers and engineers	Workers	>0.05	3.4	0.3	35	>0.05	1.8	0.9	2.2
25–54 y.o.	55–64 y.o.	0.05	2.1	1.09	5.6	0.001	2	1.05	4.8

Table 9.

Multivariate cox regression analysis of sleep disorders and risk of stroke in the 25–64-year-old population over 16-year-period.

We found that only widowed men with sleep disorders had an increased risk of stroke HR = 1.9 (95%CI 1.2–3; P < 0.01) compared to married men without sleep disorders. No significant results have been found for women. When comparing the risk of stroke among people with sleep disorders who differ in education level, it was found that the risk of stroke was higher in men with incomplete secondary/primary education HR = 5.3 (95%CI 1.4–19.1; p < 0.01) than in women HR = 4.2 (95% CI 1.25–14; p < 0.05). There was also an increased risk of stroke in women with secondary education and sleep problems HR = 3.7 (95%CI 1.1–11.9; P < 0.05). We found no differences in the risk of stroke in people with sleep disorders in the older age group 55–64 years between men HR = 2.1 (95% CI 1.09–5.6; p < 0.05) and women HR = 2 (95% CI 1.05–4.8; P < 0.001) (see Table 9).

A single-factor regression analysis showed that in a population of men aged 45–64 years, the risk of developing MI, over a 14-year period, in men with 5–6 hours of sleep was 1.689 higher (95%CI 1.124–2.537; p < 0.012) compared with men with 7–8 hours of sleep. The risk of MI in the group of men aged 45–54 years with 5–6 hours of sleep over a 14-year period was 2.416 (95%CI 1.311–4.452; p < 0.005) compared with men with 7–8 hours of sleep per night (see Table 10).

	Risk factor	Reference group	p	HR	95% CI for HR
Age group	number of hours slept	Number of hours slept			Lower bound	Upper bound
45–64 y.o.	5–6 hours	7–8 hours	0.012	1.689	1.124	2.537
45–54 y.o.	5–6 hours	7–8 hours	0.005	2.416	1.311	4.452
55–64 y.o.	5–6 hours	7–8 hours	0.870	1.067	0.491	2.322
45–64 y.o.	7–8 hours	9–10 hours	0.355	1.218	0.802	1.850
45–54 y.o.	7–8 hours	9–10 hours	0.086	1.965	0.910	4.245
55–64 y.o.	7–8 hours	9–10 hours	0.433	0.775	0.409	1.467
45–64 y.o.	9–10 hours	7–8 hours	0.282	0.578	0.213	1.570
45–54 y.o.	9–10 hours	7–8 hours	0.289	0.045	0.001	13.840
55–64 y.o.	9–10 hours	7–8 hours	0.310	1.709	0.607	4.809

Table 10.

14-year risk of myocardial infarction in men aged 45–64 years (screening IV) by number of hours of night sleep (single-factor cox regression model).

In the population of women aged 45–64 years, according to a single-factor Cox regression analysis, over a 14-year period, the risk of MI was 1591 (95%CI 1058-2392; p < 0.026) higher among people who slept 5–6 hours compared with women who slept 7–8 hours per night. In the 45–54-year-old group, the risk of MI was 4.44 (95%CI 2726-20,309; p < 0.0001) higher for women who slept 9–10 hours per night compared to women who slept 7–8 hours per night (see Table 11).

	risk factor	reference group	p	HR	95% CI for HR
Age group	number of hours slept	number of hours slept			Lower bound	Upper bound
45–64 y.o.	5–6 hours	7–8 hours	0.026	1.591	1.058	2.392
45–54 y.o.	5–6 hours	7–8 hours	0.628	0.764	0.257	2.270
55–64 y.o.	5–6 hours	7–8 hours	0.487	0.688	0.239	1.977
45–64 y.o.	7–8 hours	8–10 hours	0.747	0.938	0.634	1.386
45–54 y.o.	7–8 hours	8–10 hours	0.006	0.292	0.121	0.706
55–64 y.o.	7–8 hours	8–10 hours	0.398	1.420	0.629	3.207
45–64 y.o.	9–10 hours	7–8 hours	0.105	1.712	0.894	3.280
45–54 y.o.	9–10 hours	7–8 hours	0.0001	4.440	2.726	20.309
55–64 y.o.	9–10 hours	7–8 hours	0.368	0.045	0.0001	38.406

Table 11.

14-year risk of myocardial infarction in women aged 45–64 years (screening IV) by number of hours of night sleep (single-factor cox regression model).

4. Discussion

According to our data, in the age group of 25–64 years, the level of sleep disorders is high and had the following trend: from 1988 to 1989 to 1994–1995, there was a decrease; however, an increase was observed in 2003–2018. The increase in sleep disorders between 2003 and 2018 was mainly due to older age groups (45–64 years). Our results on the increase in sleep disorders in 2003–2018 are consistent with data from other researchers. For example, Calem M. and co-authors conducted three cross-sectional mental health studies in 1993, 2000 and 2007 in the UK and found that the prevalence of sleep disorders in the adult population of England is slightly but steadily increasing [33]. In the United States, insomnia or sleep problems were reported to have increased significantly in the adult population between 2002 and 2012 [34]. In addition, from 1999 to 2010, the number and percentage of outpatients who complained about sleep problems in the United States increased significantly, as did the number of prescriptions for sleep medications [35]. In Norway, the prevalence of several different symptoms associated with sleep disorders, as well as clinical cases of insomnia and the use of sleep medications, increased significantly in the adult population between 1999 and 2010 [36]. In Finland, symptoms related to insomnia and daytime sleepiness doubled from the mid-1990s to the late 2000s [37]. However, some of our results were unexpected, i.e., the level of sleeping disorders decreased in 1994–1995 (the screening III). For an explanation of the seemingly paradoxical indicators, we turned to our previous work on trends in self-rated health. It was during this period that the majority of the population lost their jobs, withdrew into the family circle, and looked for new jobs, which could affect the nature of sleep [38, 39]. But this does not mean that it was a healthier sleep, because we got a decrease in the number of “very good sleep” responses and an increase in “satisfactory” responses. The increase in sleep disorders in 2003–2015 is due to the fact that social and economic conditions have changed: socio-economic factors (income, level of education and employment status - an increase in the amount of work due to lack of financial resources, the need to work in shifts, shifting the time of falling asleep) naturally lead to sleep disorders [40]. Adequate uninterrupted sleep is becoming rare, especially in 24/7 communities [5], and short sleep (<6 hours/night) is increasingly observed, especially among full-time workers [6]. Women were found to have twice as many sleep disorders as men. This is in agreement with the results obtained by other authors [41]. According to our data, which is also emphasized by other authors [42, 43], the prevalence of sleep disorders increases with age. It should be noted that some age groups show trends different from the general trend. Thus, there is a trend toward a decrease in sleep disorders in women in the age groups 25–34 and 35–44. A decrease in sleep disorders in men aged 35–44 years was observed in 2013–2016. This is understandable, given that the frequency of sleeping problems also depends on psychosocial factors [44]. It was found that over 22 years (from 1994 to 1995 to 2013–2016), high levels of hostility, life exhaustion, and low levels of social support decreased significantly among women aged 25–44. Low levels of social support decreased significantly among men aged 35–44 years [39, 45].

Among the population aged 45–64, during the observation period from 2003 to 2005 to 2015–2018, the number of people sleeping 5 hours or less per day increased 1.6 times for men and more than 2 times for women. Although according to our data, mainly in the population studied, the population spent from 7 to 8 hours of sleep, we do observe an unfavorable trend: over the past period, the number of people spending the recommended ≥7 hours of sleep in our population has decreased [10]. The result obtained is not only typical for our population but also has a global trend. For example, Liu Y. and co-authors, 2016 [46] showed that nearly two-thirds of adults in the United States sleep ≥7 hours per day, and approximately 83.6 million adults in the United States sleep <7 hours. In a comparative analysis between two age groups, 45–54 years and 55–64 years, using the example of the screening IV, we found that 5, 7, 8, 9 and 10 hours of sleep were more common among people aged 55–64 years, and 6 hours of sleep was more common in the 45–54-year group. The need to adapt to a modern lifestyle is one of the possible reasons for the predominance of 6-hour sleep in the 45–54 age group. For example, short sleep duration (<6 hours/night) has become increasingly common in the active working-age population working full time [47]. Also, based on data from the world literature, one of the reasons for the increase in the number of people aged 55–64 years who sleep ≤5 hours or ≥ 9 hours every night is lack of physical activity [48]. The duration of sleep is one of the many factors that may have a potential impact on physical activity [49]. In particular, Tsou [50] found that study participants who were “long sleepers” (≥9 hours) were less likely to engage in regular physical activity. Another study conducted among elderly people living in the Chinese community showed that both short and long sleep duration were associated with poor physical performance compared to people who reported 7–8 hours of sleep [51]. Looking at the dynamics of sleep for the period from 2003 to 2005 to 2015–2018, it was found that regardless of gender and age, there was an increase in 5–6 hours of sleep in 2015–2018 compared to 2003–2005, when sleep duration was more often 7–8 hours, which again confirms the global trend [51]. Our results are also consistent with the ESSE-RF study, the average age of the population is ±50 years, which showed that the average sleep duration in different regions of Russia was 7.3 ± 1.2 hours. At the same time, 22.5% of participants had a sleep duration of 6 hours or less per day, and 12.4% of respondents had more than 9 hours per day [41]. We also analyzed the effect of sleep duration on sleep quality. It turns out that in 2003–2005 those who slept 8 hours a day were more likely to think their sleep was “good”; in 2015–2018 those who slept 7 hours a day were more likely to think so. An unexpected trend was found in the male population: those who slept 6 hours were more likely to say their sleep was “good”, and those who slept 7 hours were more likely to say their sleep was “bad”. On the contrary, a comparative analysis of women showed that those who slept 7 hours per day rated their sleep as “good sleep”, and those who slept 6 hours - as “poor sleep” [52]. We turned to the monograph of Horne J. A. Journey Through the Science of Sleep [53] for the explanation. For women, “poor sleep” is closely associated with high levels of psychological distress and increased feelings of hostility, depression, and anger; these feelings were not associated with the same level of sleep disturbance in men. Allowing the brain to recover is one of the primary functions of sleep. The more mental activity a person engages in during the day, the more time it takes for the brain to recover and, therefore, the more sleep that is needed. Women tend to be multi-taskers - they do a lot of things at the same time and they have more neuroplasticity - and so they use up more of their mental energy than men do. As a result, their need for sleep is greater. A man who has a difficult job that requires a lot of decision-making and outside-the-box thinking may also need more sleep than the average man, although probably not as much as a woman.

Our results are consistent with the data obtained by Swedish researchers. They conducted telephone interviews with 1550 men and women between the ages of 18 and 84. Women were found to report sleep problems twice as often as men [57]. This is confirmed by other authors such as Zhang B, Wing YK. In 2006, a meta-analysis of 31 sources concluded that women are 1.4 times more likely to suffer from sleep disorders than men [58]. As shown by Barsky AJ and coauthors in 2001, this is because women are more likely than men to express emotional experiences and somatic symptoms, including sleep complaints [59]. In addition, as an explanation for the discrepancy between men and women in the prevalence of insomnia, Lampio L. and co-authors have shown that in women, sleep disorders may occur due to a decrease in estrogen and progesterone levels. Thus, postmenopausal women (aged 53–58) were more likely to wake up at night compared to premenopausal women (aged 44–48) [60].

Widowed men were 2.6 times more likely than women to develop hypertension. This is explained by the fact that loneliness, especially as people get older, is usually associated with a stressful situation. These include retiring, separating from relatives, and losing a spouse [61]. Being widowed or bereaved ranks among the most stressful situations. When a widowed person lives on his or her own, he or she has to face many practical and psychological problems. They have to manage their own household, maintain social contacts and make financial decisions. It is believed that men who are lonely in old age have a harder time bearing it than women do. The reason for this is not only the emotional restraint of men but also the fact that, unlike women, they adapt less well to the new situation. Widows tend to keep in touch with family and friends, and their social lives tend to be more intense. Widowers are more likely to become isolated and disrupt pre-existing social contacts because the relationship between fathers and children is less predictable than with the mother and can change for the worse. The loneliest widows are those with few or no children. Despite the fact that widowers tend to have higher incomes, they have fewer health problems than widows, but more emotional problems. The risk of social isolation increases for many older people who have experienced the death of a spouse. The different attitudes to loneliness among men and women support the view that the experience of loneliness is a purely individual feeling that does not transcend external conditions [62]. Thus, the combination of loneliness, dissatisfaction with life, and additional household chores contributes to poor sleep quality [57] and further increases the risk of developing hypertension [63, 64]. In our study, the risk of developing hypertension in women with incomplete secondary or primary education was three times higher than in women with secondary education. This is in line with the results obtained by Chen Y. in 2005: the higher the level of education of women, the better their sleep; on the contrary, men with a low level of education sleep better [65]. Only women, but not men, who rated their sleep as “bad” and had an average and low level of education, had an increased risk of developing hypertension. Our results are consistent with the conclusions of other authors who consider a low level of education as an independent risk factor for hypertension [66]. There were no gender-related differences in the occupational risk of hypertension. Our study has shown that sleep disorders are more common in women than they are in men. In addition, the presence of an unfavorable social gradient, e.g., widowhood or low educational level, contributes to an increased risk of hypertension. Nevertheless, we observe that the increased risk of hypertension is greater in men (HR = 5.4) than in women (HR = 4.35) during the first 5 years after the start of the study. Within 10 years, the risk of hypertension is about the same for men and women. It decreases by the 16th year. What is the reason for this? It is known from the literature that there are gender differences in coping with stress [67] and in the effects of stressful life events [68]. We believe that sleep disorders, as one of the psychosocial factors, contributes to the risk of hypertension, independent of other factors, in both men and women, but additional conditions, such as a negative social gradient, contribute to aggravate the situation.

The risk of myocardial infarction and stroke was higher in men with dysfunctional marital status and sleep disorders, while we did not find such patterns in women. Notably, the highest risk of heart attack and stroke was among widowed men with sleep disorders. One of the most stressful events in life is the loss of a loved one, which often leads to severe emotional disturbance, reduced financial security, and lifestyle changes, all of which contribute to poor sleep quality [69]. We also found that the risk of stroke was highest in people with low levels of education and sleep disorders, in both men and women. Sleep disorders increased the risk of myocardial infarction by 2.4 times in men aged 25–64. We found that in women with sleep disorders, the risk of myocardial infarction was 2.6 times higher only at the age of 55–64 years; in men in this age group, the risk of myocardial infarction was the highest - 6.4 times. The results obtained are confirmed by other researchers. For example, Gianfagna F. together with co-authors, found that severe sleep disturbance increased the risk of CVD by a factor of 1.8 for first-time sleep disturbance and by a factor of 1.97 for those over 48 years of age [70]. Men who slept no more than 5 hours per night had a 2.3 times higher risk of developing a heart attack than men who slept 6 to 8 hours per night [54, 71].

The risk of stroke in people with sleep disorders was higher in men (HR = 3) than in women (HR = 1.9), but after adjusting for social gradient and age, the risk of stroke was similar in men (HR = 2.8) and women (HR = 2.7). It is known from literature that a stroke can be preceded by various sleep disorders. These include insomnia, fatigue, increased sleepiness, and parasomnia [72]. One of the major risk factors for stroke is sleep-disordered breathing, such as snoring. Sleep disorders and sleep-disordered breathing affect general and cerebral circulation. This leads to hypoxemia during the night. The high prevalence of morning strokes supports this theory. Oxygen demand is higher during REM sleep, and most apnea occur during this stage [73]. Eguchi K and coauthors conducted a study to determine the effect of sleeping time on stroke risk. The risk of stroke was more than doubled in hypertensive patients with less than 7.5 hours of sleep per night [74].

In our study, over a 14-year follow-up period, the risk of myocardial infarction was almost 1.7 times higher in men aged 45–64 years, and 2.4 times higher in the 45–54 years group, in those who slept 5–6 hours compared with those who slept 7–8 hours. In women aged 45–64, the risk of MI was almost 1.6 times higher among those who slept 5–6 hours compared to those who slept 7–8 hours. And the greatest risk of MI was in the 45–54-year-old group. The risk is 4.44 times higher in women who sleep 9–10 hours per night compared to women who sleep 7–8 hours per night. Our results are similar in many respects to those of the MONICA/KORA Myocardial Infarction Registry Study, Augsburg, Germany [54]. Over a 10-year follow-up period, compared with women who slept 8 hours, the relative risk (HR) of myocardial infarction was 2.98 (95% CI, 1.48–6.03) for women who slept less than 5 hours and 1.40 (95% CI 0.74–2.64) for women who slept ≥9 hours. The corresponding HRs for men were 1.13 (95% CI 0.66–1.92) and 1.07 (CI 95%, 0.75–1.53), respectively [54]. Another study confirming our results was conducted by Daghlas I. and coauthors [55]. They studied the relationship between sleep duration and MI, taking into account the genetic risk of coronary artery disease, as well as other parameters of sleep disorders. It turned out that compared with people who slept 6 to 9 hours every night, “short sleepers” had a 20% higher risk of MI (HR = 1.20; 95% CI, 1.07–1.33) and “long sleepers” had a 34% higher risk (HR = 1.34; 95% CI, 1.13–1.58), adjusted for several variables; associations were independent of other risk factors for sleep disorders. Healthy sleep duration reduced the risk of MI even in people with a high genetic predisposition to MI (HR = 0.82; 95% CI, 0.68–0.998) [56].

5. Conclusion

Summarizing the results of the study, we can conclude that there is an unfavorable trend - sleep duration in the population aged 45–64 years decreased between 2003 and 2018, both among men and women; there was an increase in sleep disorders. From the point of view of prevention of cardiovascular diseases, the duration of sleep from 7 to 8 hours a day may be optimal for health. However, sleeping for 9 hours or more per day can be a useful diagnostic tool in the detection of subclinical or unrecognized co-morbidities. People who report sleeping 5 hours or less per day should be considered as a group at increased risk of all-cause mortality. In our study, “short” sleep duration was a potential risk factor for MI in men, and “short” and “long” sleep were found to be risk factors for MI in women. The question of whether sleep duration is a cause or a sign of poor health should be addressed in future research. To date, indirect evidence suggests that prolonged sleep deprivation may trigger biological mechanisms that contribute to poor health, while prolonged sleep duration may be a strong additional marker of poor health. Sleep duration should be considered as an additional behavioral risk factor or risk marker that is largely determined by the environment and may be amenable to change through education and counseling as well as public health interventions. It is necessary to seek favorable changes in the physical and work environment to ensure adequate sleep and to avoid habitual and prolonged sleep deprivation.