Clinical utility of serum 25-hydroxyvitamin D in the diagnosis of insulin resistance and estimation of optimal 25-hydroxyvitamin D in U.S. adults

Association between vitamin D serum levels and insulin resistance assessed by HOMA-IR among non-diabetic adults in the United States: Results from NHANES 2007-2014

Insulin resistance, a pathological response to insulin hormone in insulin-dependent cells, is characterized by the presence of high glucose and insulin concentrations. The homeostasis model of insulin resistance (HOMA-IR) is one of the most used indexes to estimate insulin resistance by assessing the fasting glucose and insulin levels. An association was observed between vitamin D levels and insulin resistance, which varied in different ethnic groups, and there is some evidence that vitamin D supplementation could contribute to the improvement of insulin resistance. This study assessed the association between 25-hydroxyvitamin D (25[OH]D) concentration and HOMA-IR in American adults aged 20 years and older, without diabetes and other chronic diseases that can influence insulin resistance. The data from the National Health and Nutrition Examination Survey (NHANES) 2007–2014 were used by exploiting the free and publicly-accessible web datasets. Linear regression models were performed to evaluate the association between serum 25(OH)D concentration and HOMA-IR, and a negative association was observed, which remained significant following the adjustment for age, gender, race/ethnicity, education, body mass index (BMI), physical activity, the season of examination, current smoking, hypertension, the use of drugs which can influence insulin resistance, serum bicarbonates, triglycerides, and calcium and phosphorus levels. Only in non-Hispanic Blacks was this inverse association between vitamin D and HOMA-IR not observed in the fully adjusted model. Further studies are needed to explain the mechanisms of the observed ethnic/racial differences in the association of vitamin D levels with HOMA-IR.

Association between vitamin D deficiency and insulin resistance markers in euthyroid non-diabetic individuals

AIM

To evaluate the association between vitamin D deficiency and insulin resistance (IR) or hyperinsulinemia after oral glucose tolerance test (OGTT) in euthyroid non-diabetic individuals.

MATERIALS AND METHODS

We carried out an analytical cross-sectional study in euthyroid non-diabetic adults of both sexes, who attended the outpatient service of a private clinic in Lima-Peru during the 2012-2016 period. Participants were categorized in two groups according to their serum vitamin D levels: normal vitamin D levels (serum vitamin D values ≥ 20 ng/dL) and vitamin D deficiency (serum vitamin D values < 20 ng/dL). IR was defined as a Homeostasis Model Assessment (HOMA-IR) value ≥ 3.8 and hyperinsulinemia after OGTT was defined as a serum insulin value ≥ 80μU/mL after 120 min of 75-g glucose intake. We elaborated crude and adjusted Poisson regression models to assess the association between serum vitamin D levels and IR or hyperinsulinemia after OGTT. The reported association measure was the prevalence ratio (PR) with their respective 95% confidence intervals (95%CI).

RESULTS

We analyzed 204 participants, the average age was 38.5 ± 10.6 (SD) years, 40 (19.6%) were males and the vitamin D median was 25.0 (IQR: 19.0-33.3) ng/dL. The prevalence of vitamin D deficiency, IR and hyperinsulinemia after OGTT was 29.4% (n = 60), 29.9% (n = 61) and 25.0% (n = 51). In the adjusted Poisson regression models, the prevalence of hyperinsulinemia after OGTT was higher among the vitamin D deficient group (aPR=1.75; 95%CI: 1.06-2.90); however, we did not find statistically significant association between vitamin D deficiency and IR (aPR=0.99; 95%CI: 0.61-1.63).

CONCLUSIONS

We found an association between vitamin D deficiency and hyperinsulinemia after OGTT in euthyroid people with no T2DM.Our findings are consistent with previous reports; providing evidence that serum vitamin D deficiency could be an IR marker.

Serum Nutrient Levels and Aging Effects on Periodontitis

Periodontal disease damages tissues as a result of dysregulated host responses against the chronic bacterial biofilm insult and approximately 50% of US adults >30 years old exhibit periodontitis. The association of five blood nutrients and periodontitis were evaluated due to our previous findings regarding a potential protective effect for these nutrients in periodontal disease derived from the US population sampled as part of the National Health and Nutrition Examination Survey (1999⁻2004). Data from over 15,000 subjects was analyzed for blood levels of cis-β-carotene, β-cryptoxanthin, folate, vitamin D, and vitamin E, linked with analysis of the presence and severity of periodontitis. Moderate/severe disease patients had lower cis-β-carotene levels across all racial/ethnic groups and these decreased levels in moderate/severe periodontitis were exacerbated with age. β-cryptoxanthin demonstrated lower levels in severe disease patients across the entire age range in all racial/ethnic groups. Folate differences were evident across the various age groups with consistently lower levels in periodontitis patients >30 years and most pronounced in females. Lower levels of vitamin D were consistently noted across the entire age range of patients with a greater difference seen in females with periodontitis. Finally, an analytical approach to identify interactions among these nutrients related to age and periodontitis showed interactions of vitamin D in females, and folate with race in the population. These findings suggest that improving specific nutrient intake leading to elevated blood levels of a combination of these protective factors may provide a novel strategy to affect the significant increase in periodontitis that occurs with aging.