Elevated Non-fasting Plasma Total Homocysteine Level is Associated with Alveolar Bone and Tooth Loss: Insights for Osteogenic Innovations

Abstract

Tooth loss can cause functional impairment, in terms of chewing/mastication ability and choice of foods/diet, leading to malnutrition, which might ultimately impact general health and well-being. No studies on homocysteine (Hcy), an inflammatory sulfur-containing amino acid biomarker, levels, and tooth loss (or number of remaining teeth), are present. This study opted to obtain data from the available National Health and Nutrition Examination Survey III (NHANES III) and perform statistical analysis to investigate the association between tooth loss and tHcy (plasma/serum levels), with a focus on the elderly population. Acquired data for 1568 individuals aged 65 years or older were then tabulated, to detail. Age, gender, cholesterol, income, education, exercise, creatinine, systolic blood pressure, body mass index, and dental state were each found to be independently associated with tHcy. In a multiple regression model, only age (ρ < 0.0001), education (ρ < 0.0001), creatinine (ρ < 0.0001), and dental state (ρ < 0.003) were significantly associated with tHcy, explaining 22% of the variation detected in log-[tHcy]. Plasma Hcy levels in patients are associated with dental status and can be notably affected with oro-dental health, socioeconomic status, and access to therapeutic interventions. Considering these findings, tHcy level monitoring (to diagnose vitamin B6, B9/folate/folic acid or B12 deficiency) as well as nutritional counseling and vitamin supplementation (rechecked post-8 weeks) should be considered and incorporated into the diagnostic and treatment plan for the edentate/edentulous elders, especially if other cardiovascular or inflammatory risk factors are present. In the context of osteogenesis and oral health, research exploring the relationship between elevated Hcy levels and alveolar bone, and tooth loss can provide valuable insights into the underlying mechanisms of bone metabolism and dental health. Understanding how Hcy levels impact bone density, bone remodeling processes, and periodontal health can potentially lead to the design, innovation, development, and translation of novel therapeutic approaches and preventive strategies for osteoporosis, periodontal disease, as well as tooth loss.

1. Introduction

According to the US-CDC (Centers for Disease Control and Prevention, the national public/federal health agency of the United States under the Department of Health and Human Services, headquartered in Atlanta, Georgia), about 1 in 6 (17%) adults aged 65 or older have lost all their teeth (Figure 1). Thus far, the two most prevalent oral diseases and causes of tooth loss continue to be caries/decay and periodontal disease. Also, more than 1 in 3 adults aged 65 or older who were from the low-income group, had less than a high school education and were smoking cigarettes (2011–2016) lost all their teeth/dentition. Severe tooth was found to be 50% higher in those with fair or poor general health status suffering from asthma, heart disease, diabetes, liver conditions, emphysema, rheumatoid arthritis, and with a history of stroke, when compared to people without these chronic conditions. Indeed, it is today well recognizable that tooth loss and severe tooth loss affect Oral Health-Related Quality of Life (OHRQoL), overall QoL, well-being, successful/comfortable aging, and longevity [1, 2]. All of these factors are thought to be closely associated with the quality of the diet [3]. Further, it is well established that socioeconomic status affects diet and, consequently, QoL and OHRQoL, especially in older people (ρ low intake of certain types of foods, nutrients, and minerals). Logically, a poorer diet (quality) often costs less, and while it might be more energy-dense, and it is often more nutrient-poor [2]. In 2019, Nakamura et al. [4] conducted a cross-sectional analysis of data from 2049 Japanese individuals aged ≥50 years, concluding that having a few/fewer remaining teeth was associated with a low nutrient intake and low serum albumin levels, evident in individuals from the low socioeconomic group (with annual household income of <2 million Japanese yen: estimated at ~14,500 USD; equivalent household expenditure per month). The study emphasized the importance of promoting oral and dental health (as well as dietary strategies) in low-income, middle-aged, and older people to help sustain an adequate nutritional status [4].

Figure 1.

Geriatric oral health and tooth loss. CDC correlation between tooth loss and socioeconomic factors in the elderly (TOP). Dentition loss classification and traditional treatment options for rehabilitation (BOTTOM-left). Analytical data source: US-CDC/NCHS and laboratory testing included in NHANES III (BOTTOM-right).

Further, severe loss of teeth, particularly complete edentulism, has been associated with the reduced/diminished ability to properly chew/masticate foods (hence leading to a preference for easy-to-consume/-swallow diet that is often richer in fat or dairy products), with poor general health and increased mortality, even when socioeconomic factors are taken into account [5]. Edentulism has indeed been linked to an increase in the prevalence of coronary disease [6, 7], stroke [8], dementia [8, 9], cancer [5], and diabetes [10]. Indeed, almost two decades ago, Joshipura et al. [11, 12] tackled this nutritional state link and found that the average intake of dietary fiber, vegetables, and fruits decreased with the loss of teeth, noting that in parallel, the consumption of calories and saturated fat increased. Similar findings have been reported by other authors and studies [3, 4, 13, 14]. Therefore, it can be stated herein that the impact on QoL and OHRQoL of disease as well as oral and dental rehabilitation (Figure 1) and its termed (short vs. long) consequences should be taken into consideration when assessing the overall health status and evaluating the clinical outcomes of therapeutics.

Herein, with recent advances in diagnostic technologies and multi-disciplinary strategies, there is accruing evidence that inadequate intake of certain nutrients, even at a level insufficient to cause classical deficiency syndromes, is linked to cardiovascular disease, neural tube defects, and cancer [15]. For example, plasma homocysteine (tHcy), a sulfur-containing amino acid (Figure 2), found to be increased/elevated in various inflammatory conditions, can be considered as a functional (inflammatory) biomarker of the nutritional status and a novel and independent risk factor for cardiovascular disease, among others. This is due to the fact that total plasma homocysteine concentration (tHcy) varies with the intake of the group B vitamins, namely folate/folic acid, B12, and B6 [16], making it sensitive to metabolic changes according to or dependent on the intake of fresh fruit, vegetables, and meat [17]. Indeed, higher tHcy levels are associated with increases (risk) in cardiovascular disease, as mentioned earlier, in addition to peripheral artery disease, deep vein thrombosis, renal disease, dementia, and cognitive dysfunction in the elderly [18, 19, 20]. For instance, tHcy >14.4 μmol/L is now associated with twice the risk of carotid stenosis when compared with low plasma homocysteine (< 9.1 μmol/L), after correction for other factors [21]. In addition, to simplify to the reader, it has been estimated that an increase in tHcy of 1 μmol/L is associated with a 10% increase in risk of cardiovascular disease [22]. Furthermore, tHcy levels have been correlated with other risk factors and major lifestyle determinants, including gender (male), age, smoking, and consumption of coffee [18]. An evident association with chronic periodontitis (as an inflammatory disease) was recently demonstrated in otherwise systemically healthy individuals. For example, in a case-control hospital-based study involving 85 age- and sex-matched subjects with chronic periodontitis and 91 healthy controls, elevated tHcy was observed in patients/cases [23]. In another recent longitudinal case-control clinical study [24], with a total of 60 patients, tHcy levels (measured by high-performance liquid chromatography analysis) were compared at baseline and 12 weeks post-periodontal (non-surgical) therapy. Interestingly, the mean levels of plasma Hcy were found to be low in the control group, whereas found to be higher in the test group, at baseline [24]. Both tHcy levels and all the detected periodontal parameters were reduced significantly, after intervention, yet were not reduced in cases to levels comparable to controls/periodontally healthy individuals [25]. Nonetheless, for patients at high risk of cardiovascular diseases, for example, periodontal therapy can perhaps be a useful or helpful Hcy-lowering adjunct procedure, worthy of appraisal, a topic of current research, development, and innovation.

Figure 2.

Homocysteine. Hcy molecular structure, mechanistic pathway, and its role in patient overall health, general well-being, and quality of life (QoL).

As depicted in Figure 2, and recently reported by Debreceni and Debreceni [25], the group B vitamins do play an essential role in the Hcy metabolism pathway (transformation and excretion: trans-methylation reactions forms Hcy ρ oxidized biomolecule bound to plasma proteins ρ which is then re-methylated back to methionine or is converted into cysteine in trans-sulfuration reactions). For instance, the re-methylation reaction requires, among others, vitamin B9 as substrate and vitamin B12 as a co-factor, hence why Hcy can be considered a functional marker for the systemic availability of B9 and B12 [26]. In an edentulous patient, it can be stated that despite advances in rehabilitation, prosthodontics, and dentures, and given ample limitations or hurdles (such as functional/esthetic expertise, availability/accessibility, and cost issues), masticatory/chewing ability is not yet fully or adequately restored. Indeed, a 2018 randomized, cross-over, and double-blinded clinical trial [27] compared, through masticatory tests and a questionnaire, the feeling of retention, stability, and accumulation of particles below the removable denture (complete) among patients with and without adhesives, hypothesizing that the use of adhesives for enhanced retention stability does not increase patient satisfaction with their dentures [27]. Such studies aiming to promote patient experience and satisfaction with removable dentures as a decisive factor in therapeutic or rehabilitative success (with a clear impact on OHRQoL and QoL), continue, especially in low socioeconomic populations, with limited to no access to superior implant-supported overdentures [28, 29, 30], for example, which have reported significant improvements in masticatory ability and improved nutritional state, yet, to the best of knowledge no studies have investigated correlations with tHcy levels. Further, despite accruing reports focusing on periodontal diseases, none on tooth loss and tHcy were found in the available literature ρ Nakamura et al. [4] investigated serum albumin and hemoglobin levels as the nutritional biomarkers associated with the number of teeth – in quadrants), thus triggering the present analysis.

Herein, data from the National Health and Nutrition Examination Survey III (NHANES III), an accessible and readily available program of health-related studies (one of a series conducted by the CDC and its National Center for Health Statistics or NCHS – oversampling GIS Data/FTP file server; can visit survey methods, sample design, datasets, weighing procedures, analytical guidelines and related documentation at the US Department of Health and Human Services and/or the CDC/NCHS-NHANES (Figure 1) combining interviews/questionnaires and physical/clinical/laboratory examinations, designed cross-sectionally to assess the health and nutritional status of adults and children (random sampling selection) in the United States, representative of the non-institutionalized civilian population, was employed to test the hypothesis that tooth loss and edentulism associated with elevated serum homocysteine concentration, in the elderly (> 65 years).

2. Materials and methods

Using the SAS Universal Viewer (SAS Institute Inc., NC, USA), data from male and female individuals of all races who were 65 years or older were included in the analysis, as well as factors known to influence tHcy: age (years), gender (male, female), smoking status, alcohol consumption, serum creatinine levels (mg/dl), total cholesterol (mg/dl), systolic blood pressure (mmHg), socioeconomic status (represented by education and income), coffee consumption, exercise, body mass index (kg/m²), and dental status. Because our hypothesis was that elevated tHcy might be caused by wearing dentures, the dental status has opted to be defined as binary or dichotomous: teeth in both arches versus no teeth in at least one arch. Definitions of smoking status, alcohol and coffee consumption, education, income, and exercise are obtainable in the ‘APPENDIX’.

2.1 Statistical analysis

First, linear regressions of the continuous dependent variable log[tHcy] were carried out on each of the identified potential predictors. Three highly skewed variables – tHcy, creatinine, and income – were logarithmically transformed before inclusion into the statistical examination, analysis, and interpretation. Subsequently, forward selection was employed to construct a multiple linear regression model for log[tHcy] using only those independent variables that were found to be significant in the performed univariate analysis. For sensitivity analysis, the model was also fitted using backward selection, resulting in reassurance that both model-building strategies lead to the same model.

3. Results

The Third National Health and Nutrition Examination Survey (NHANES III) provided data on 2445 males (47%) and 2807 females (53%). Table 1 summarizes the basic characteristics of the study population. Note that information on the dental state was only available for 1568 subjects. The mean age of those surveyed was 75.7 years, with an average income of $23,200 and less than 10 years of formal education. Mean body mass index (BMI) was 26.6 kg/m² (males = 26.1 kg/m²; females = 26.9 kg/m²). The table also describes the mean concentrations of cholesterol and creatinine (mg/dl) and mean systolic blood pressure (mmHg). Herein, the variables found to be significantly related to log[tHcy] in the single variable analyses, which used all available observations for each co-variate, were age (ρ < 0.0001), gender (ρ < 0.0001), cholesterol level (ρ = 0.0092), exercise (ρ < 0.0016), dental state (ρ < 0.0001), log [creatinine] (ρ < 0.0001), log of income (ρ < 0.0001), education (ρ < 0.0001), body mass index (ρ = 0.006), and systolic blood pressure (ρ = 0.0393), as displayed in Table 2. Our forward selection model-building strategy selected only age, education, blood creatinine, and dental state as being significantly associated with log[tHcy]. After exponentiating the model for log[tHcy] to obtain a model for tHcy, the regression coefficients were interpretable as a multiplicative effect on tHcy. For every year increase in age from 65, homocysteine levels increase by 0.6%, and a single additional year of education was associated with a 1% reduction in tHcy. As expected, higher levels of creatinine were associated with increased homocysteine levels (ρ < 0.0001). Finally, lacking teeth in at least one arch was associated with a 5% increase in tHcy (ρ = 0.003). The amount of variation in log[tHcy] explained by the model was R² = 0.22 or 22% (high-level/↑), as illustrated in Table 3. When teeth were present in both arches, tHcy was 11.7 ± 0.2 μmol/l (mean ± standard error). In contrast, the mean level in those lacking teeth, in at least one arch, was 12.7 ± 0.2 μmol/l. Missing teeth may exhibit a dose-response paradigm. While the difference was not statistically significant (ρ = 0.15), those missing teeth in only one arch had mean levels of 12.2 ± 0.4 μmol/l, whereas those missing all teeth had mean levels of 12.9 ± 0.3 μmol/l. Herein, the prevalence of hyperhomocysteinemia (> 14 μmol/l) was 20.1% ± 0.55% (ρ ± standard error) in those elders with teeth in both arches, 25.3% ± 1.3% in those with teeth in only one arch, and 29.3% ± 0.9% among the completely edentulous.

				Percentile
Variable	N	Mean	Standard Error	5th	25th	50th	75th	95th
Age (years)	5252	75.74	0.10	65	70	75	81	88
BMI (kg/m^2)	4461	26.6	0.078	19.2	23.0	26.0	29.4	35.7
Education (years)	5171	9.46	0.06	0	7	10	12	16
Poverty income ratio	4493	2.32	0.03	0.58	1.09	1.77	3.00	6.07
Cholesterol (mg/dl)	4178	220.07	0.70	151	189	217	246	296
Creatinine (mg/dl)	4089	1.22	0.01	0.8	1	1.1	1.3	1.8
SBP (mmHg)	4082	142.88	0.32	113	129	141	155	179
Homocysteine (μmol/L)	1723	12.23	0.16	6.3	8.7	10.8	13.9	22.2

Table 1.

NHANES III population characteristics.

Predictor	ß	ρ-value
Smoke cigarettes	0.0297	0.34
Age (y)	0.010	<0.0001
Gender (male)	1.75	<0.0001
Log income (poverty ratio)	−0.081	<0.0001
Education (y)	−0.0.0098	<0.0001
Log creatinine	0.66	<0.0001
SBP (mmHg)	0.00096	0.0393
Cholesterol (mg/dl)	−0.00054	0.0092
Exercise	0.071	0.00016
Drank alcohol in the last month	0.00044	0.983
Coffee	−0.00005	0.829
Edentate in at least one arch	0.096	<0.0001

Table 2.

Performed univariate analysis of tHcy predictors.

A. Predictor		ß	ρ-value
Age (years)		0.0057	<0.0001
Education		−0.0098	<0.0001
Log creatinine		0.63	<0.0001
Edentate in at least one arch 0.22)		0.052	0.003
B. Dentition Status	N	Percentage (standard error) of hyperhomocysteinemia >14 μmol/L	Mean (standard error) μmol/L
Completely edentate	498	29.3% (0.9)	12.9 (0.3)
Edentate in one arch	217	25.3% (1.3)	12.2 (0.4)
Present teeth	853	20.4% (0.5)	11.7 (0.2)

Table 3.

Performed multivariable analysis of tHcy predictors (A) and the distribution of tHcy levels according to dental status and present teeth (B).

4. Discussion

Homocysteine is an amino acid found in the blood, and elevated levels of homocysteine have been linked to various health issues, including cardiovascular disease, neurodegenerative disorders, and bone health problems. Herein, the results of this analytical study of the NHANES III database indicated that lacking all teeth in at least one arch is significantly associated with higher plasma homocysteine levels in people over 65 years. To the best of my knowledge, these findings are the first to link edentulousness with a nutritional bio-indicator of systemic health risk. We also found that plasma total homocysteine concentration (tHcy) is negatively associated with the level of education and confirmed that increasing age and plasma creatinine levels are associated with increased tHcy [18]. As described earlier, studies in the general population have revealed that people with tHcy levels between 0 and 6.3 μmol/L (38% of the population) are in the lowest risk category for coronary artery disease. Those with levels of 6.3–10 μmol/L (52%) are at moderate risk, while the 10% with the highest risk have tHcy >10 μmol/L. Based on this scale, only 5% of our study population are low risk while 50% are at high risk, with the edentulous being the most vulnerable. It has been postulated before that the increased risk of arterial disease and its consequences is mediated through the many adverse effects of Hcy on the arterial wall and on the coagulation cascade [31]. If this is true, an intervention that reduces plasma homocysteine could have a strong effect on health, survival, aging, and longevity. Implant overdentures are a good candidate worthy of further investigation in this direction. Indeed, although dentures partially restore appearance and function, it has long been accepted that they are still inadequate replacements for natural dentition [28, 29, 30]. Almost two decades ago, Hung et al. [32] studied the relationship between tooth loss and changes in the consumption of fruits, vegetables, and nutrients in a large group of male health professionals. They found that those who lost five or more teeth had a significantly greater consumption of poly-unsaturated fat and were also more likely to stop eating apples, pears, and raw carrots (harder to chew). They also, in this JADA report, noted a temporal association between tooth loss and detrimental changes in dietary intake. Evidence from other investigations also supported the observations [23, 24]. Edentulous individuals, therefore, exhibit clear changes in food selection patterns that negatively affect nutrition. This change in diet is a plausible explanation for the effect of a significantly higher plasma homocysteine in the edentulous subjects. Both folate and vitamin B6 are found in fruits and vegetables, vitamin B12 is present mainly in meat, and plasma homocysteine rises if these foods are deficient in the diet, as mentioned earlier and evident in the performed analysis. Importantly, the number of people who have lost all of their teeth (by age 65) remains shockingly high in many countries, according to the WHO, which previously reported 26% in the United States, 30% in Canada, and 46% in the United Kingdom. While the incidence has been declining over the last 30 years, the total number of edentulous cases can be expected/projected to continue to rise for many years to come. Indeed, in a report on the future needs for fixed and removable partial dentures in the United States, Douglass and Watson estimated that the need for dentures will increase to 37.9 million in 2020 [33]. It is therefore reasonable to recommend providing this sub-group of patients with better/superior dental prostheses that could aid and facilitate an increased masticatory efficiency, which in turn leads to significant improvements in diet and nutritional state, and thus better OHRQoL and QoL.

5. Conclusion

Research on the association between elevated homocysteine levels and alveolar bone and tooth loss holds significant promise for advancing our understanding of bone metabolism and oral health, and it has the potential to drive innovation in osteogenesis and dental care in the coming years [34, 35, 36, 37, 38, 39]. Diet, and its nutritious quality, is closely related to overall health and general well-being, particularly in the elderly. Poor oral and dental health is associated with low intake of certain types of foods, which can often be due to severe loss of teeth and reduced chewing ability. Indeed, while chronic diseases, such as dental caries and periodontal diseases, are also still highly prevalent and further exacerbated by poor food choices, the risk of tooth loss in old age is rendered higher and alarming, requiring rehabilitative intervention. Demand for care is functional, esthetics, and now, associated with risk for systemic and life-threatening diseases. This analytical study revealed that tooth loss and being edentulous are significantly associated with high levels of serum homocysteine, a risk factor for cardiovascular diseases, among others. Elevated homocysteine levels may increase the risk of coronary disease as well as dementia, stroke, and cancer. In light of these new findings, homocysteine monitoring may be invaluable for the geriatric edentulous patient receiving the best possible rehabilitative and prosthodontic/prosthetic care, combined with paying attention to dietary intake, nutritional profiling/counseling, and recommending vitamin (B-complex: vitamin B6, B9/folate/folic acid and B12, if deficient, and recheck after every 8 weeks) supplements.

6. Closing remarks

The association between elevated non-fasting plasma total homocysteine levels and alveolar bone and tooth loss is indeed an important topic and note-worthy research theme for potential innovations in osteogenesis in the current year of 2024. Indeed, in the context of osteogenesis and oro-dental health, research exploring the relationship between elevated homocysteine levels and alveolar bone and tooth loss can provide valuable insights into the underlying mechanisms of bone metabolism and dental health (including alveolar bone and dentition loss). Understanding how homocysteine levels impact bone density, bone remodeling processes, and periodontal health can potentially lead to the development of new therapeutic approaches and preventive strategies for osteoporosis, periodontal disease, and tooth loss. Furthermore, innovations in osteogenesis may involve novel interventions targeting homocysteine metabolism to promote bone regeneration and prevent bone loss. This could include the development of pharmacological agents, dietary interventions, and personalized treatment approaches aimed at optimizing homocysteine levels and improving bone health outcomes.

Acknowledgments

This work was supported by operating grants provided to the HAiDAR R&D&I LAB/BioMAT’X (Laboratorio de Biomateriales, Farmacéuticos y Bioingeniería de Tejidos Cráneo Máxilo-Facial), member of CiiB (Centro de Investigación e Innovación Biomédica), Faculties of Medicine and Dentistry, Universidad de los Andes, Santiago de Chile, through the ANID-NAM (Agencia Nacional de Investigación y Desarrollo, Chile and National Academy of Medicine, USA) Grant#NAM21I0022, CORFO Crea y Valida I + D + i Grant#21CVC2-183649 and FONDEF CONCURSO IDEA DE I + D, FONDEF/SUBDIRECCIÓN DE INVESTIGACIÓN APLICADA/ANID 2022, Grant código # ID22I10215.

Conflict of interest

None.

Author contributions

Conceptualization, Validation, Investigation, Resources, Writing – Original Draft Preparation, Writing – Final Manuscript Review and Editing, Funding Acquisition.

Appendix A

A.1 Defining the NHANES study variables for present statistical analysis

Smoking status was defined by the binary NHANES variable HAR3, indicating whether the subject smoked cigarettes (at the time), or not. Alcohol consumption was derived from variables HAN6HS, HAN6IS, and HAN6JS. These variables recorded how many drinks of beer, wine, and liquor, respectively, the subject had drunk in the past month. Our derived binary variable simply indicated whether the subject had reported drinking any alcoholic beverages during the past month or not. To examine the socioeconomic status, we looked at education and income separately. Education, defined by the NHANES variable HFA8R, represented the total number of years of education and varied from 0 to 17. Income was analyzed using the variable DMPPIR, which represented the poverty income ratio and was computed by dividing the observed family income category by the poverty threshold. The poverty income ratio was preferred to family income because it allows a valid comparison of the families surveyed during/over the different years. Because this variable was highly skewed, and some individuals had a poverty income ratio of zero, our income variable was defined as log (DMPPIR+1). Coffee consumption, defined by the NHANES variable HAN6FS, reflected the reported number of cups of coffee consumed per month. Physical exercise was, herein, defined by the variables HAT2, HAT4, HAT6, HAT8, HAT10, HAT12, HAT14, and HAT16. Each of these variables recorded whether the subject had engaged in a specific type of activity (for example, jogging, cycling, swimming, and/or gardening) during the past month. Our composite exercise variable simply recorded whether the subject had answered yes to at least one of these activities. The body mass index, defined by the variable BMI, is simply an individual’s weight in kilograms divided by his or her squared height in meters. Finally, the tooth loss variable was set to binary. Subjects were considered to be edentulous, if they were missing all of the teeth in one entire arch (or in both arches).