Determinants of Vitamin D in Indian Populations: Understanding the Interplay of Skin Pigmentation, Sun Exposure, and Genetic Variants.

OBJECTIVES

The present study evaluates the effects and interaction of skin pigmentation, sun exposure, and genetics on 25(OH)D3 levels among ostensibly healthy Indians.

METHODS

Vitamin D3 was estimated (N = 427) and means were compared between the sexes and study populations. Vitamin D3 was correlated with Melanin Index (MI) and Weekly Sun Exposure Scores (WSES) using Kendall's tau-b (τb). The effect of age, sex, MI, WSES, and 12 SNPs from vitamin D and skin pigmentation genes were tested on 25(OH)D3 levels using univariate and multivariate linear models.

RESULTS

A total of 76.6% of the sample were deficient, with males being more deficient than females (p = 0.0016). Deshastha Brahmin caste with lowest MI (42.91 ± 4.47) and WSES (14.4 ± 8.55) reported highest 25(OH)D3 levels (26.09 ng/mL±16.84). Tribals with higher MI (52.83 ± 7.84-58.83 ± 6.37) and WSES (21.96 ± 7.85-28 ± 0) report low 25(OH)D3 levels (13.31 ± 7.05-17.94 ± 972). Vitamin D3 was weakly correlated with MI in Bhils and Kokanas (p < 0.05) and was not significantly correlated with WSES. Multivariate regression shows only sex (p = 0.031), MI (p = 0.018), and WSES (p < 0.001) to be significant predictors of vitamin D levels as compared to age, population, and rs1426654 genotype.

CONCLUSION

Vitamin D levels vary significantly among populations with widespread deficiency seen in tribal and rural populations, suggesting population-specific environments and behavioral factors to be at play. Targeted dietary fortification is needed, and additional large-scale longitudinal and genome-wide association studies will help identify key factors responsible for vitamin D deficiency among Indian populations.