Ethnic, body composition and dietary factors as determinants of vitamin D status

Background: Vitamin D deficiency (VDD) is a worldwide problem that can take an essential part in developing many chronic diseases, including but not limited to type 2 diabetes, metabolic syndrome, and cardiovascular diseases (CVD). There are many factors that can contribute to VDD or make specific populations or individuals at higher risk to develop VDD and its related health consequences. These factors include and are not limited to the ethnic background, body composition, and dietary intake of nutrients. It has been found that South Asian Indians (SAIs) are at higher risk of developing CVD and metabolic syndrome compared to their Caucasian counterparts, and at a younger age. Also, there is a high prevalence of VDD among SAIs living in their countries or in European countries. In addition, SAIs found to have a higher deposition of fat in their visceral areas compared to Caucasians. Considering that many SAIs follow restricted diets (as many follow a vegan or a vegetarian diet), which may put them at higher risk for nutrients deficiencies; it was worthy to investigate the effect of SAI ethnicity, body composition, and micronutrients intake of calcium (Ca), magnesium (Mg), and their ratio on the vitamin D status. Vitamin D status can be assessed using serum 25-hydroxyvitamin D (s25(OH)D), serum parathyroid hormone(sPTH), and serum vitamin D binding protein (sDBP). Both dietary intake of Ca and Mg were independently associated with s25(OH)D as their deficiencies were associated with VDD. Also, the intake of both is deficient among approximately half of the US population. Some studies' efforts focused on finding the optimal dietary Ca to Mg ratio for optimal health outcomes. Since both Ca and Mg share similarities in the absorption sites and functionality, and since both are independently associated with VDD, it was worth investigating if their dietary intake ratio is associated with vitamin D status among SAIs, Caucasians, and among both of them collectively. Our primary aims were to investigate if biomarkers of vitamin D statusØŒ body composition parameters, and dietary factors are different between SAIs and Caucasians and to understand the relationship between them. Methods: Healthy SAIs and Caucasian men between 22 to 60 years of age were enrolled. Anthropometric and body composition measurements, biochemical analyses for s25(OH)D, sPTH, and sDBP, and habitual dietary intakes of Ca and Mg were obtained. Independent t-test and Mann-Whitney u test were used to report the differences between groups in their vitamin D status, body composition, and dietary intakes. Pearson or Spearman correlations were used to identify the possible associations. A P value of less than 0.05 was considered significant. Results: 30 SAIs and 30 Caucasians completed the study. Both groups did not significantly differ in their age and BMI. SAIs, compared to the Caucasians, had significantly lower s25(OH)D (22.79 ± 9.1 vs 31.24 ± 9.1 ng/mL; P <0.001) and higher sPTH concentrations (60.04 (28.9) vs 47.6 (26.2) pg/mL, P =0.045). Interestingly, sDBP levels were not significantly different between the groups. s25(OH)D was significantly associated with sPTH only among the SAIs group (rs= - 0.389, P= 0.037). Lean Mass% (LM%) and Fat-Free Mass% (FFM%) were significantly lower in SAIs. In addition, LM%, Fat Mass% (FM%), FFM%, and Android fat% correlated significantly with s25(OH)D concentration among all participants. However, none of these correlations remained significant among the SAIs group while nearly all the body composition parameters (including visceral fat %) correlated significantly with s25(OH)D concentration among Caucasians. The regression models found that race was the primary predictor of s25(OH)D levels, followed by Android fat%. Race and Android fat explain ~ 20 % and 9% of the variability in s25(OH)D levels. Dietary intakes of both Ca (a median of 593 mg/day) and Mg (a median of 228 mg/day) were lower among the SAIs compared to their Caucasian counterparts (a median of 911.0 mg/day, and a median of 233.1 mg/day for Ca and Mg, respectively). The median Ca and Mg intakes were all below the RDA for Ca and Mg. However, this difference did not reach statistical significance. This study found that the median Ca: Mg ratio was (3.3 (2.7)) among Caucasians and (3.9 (2.2)) among SAIs. None of the dietary factors correlated significantly with the biomarkers of vitamin D status measured in this study. Conclusion: SAIs had lower s25(OH)D and higher s(PTH) levels, and the relationship between these biomarkers seems to be more interrelated among SAIs compared to their Caucasian counterparts. SAIs in this study had less favorable body composition parameters (Less LM% and FFM%). Race and android fat% were significant predictors of s25(OH)D levels. Future studies and clinical practices should consider frequent screening for VDD among SAIs as a high-risk group, and enhancing the SAIs' physical activity to improve their body composition. It is also essential to consider providing dietary or supplemental vitamin D, Ca, and Mg in an optimal ratio that meets each ethnic group's needs, since needs for these microminerals differ by ethnicity.