Association between vitamin D deficiency and type 2 diabetes in an Indigenous Brazilian population

This study investigated the association between vitamin D levels and type 2 diabetes mellitus (T2DM) among Indigenous adults of the Tupiniquim and Guarani ethnicities residing on a reserve on the southeastern Brazilian coast.

This cross-sectional study, conducted between 2020 and 2022, included 946 Indigenous individuals (aged ≥20 years, both sexes) from the Tupiniquim and Guarani ethnic groups. T2DM was defined by a self-reported diabetes diagnosis, the use of glucose-lowering medications, or, in the absence of such reports, a fasting plasma glucose level ≥126 mg/dL, a 2-hour plasma glucose level ≥200 mg/dL following an oral glucose tolerance test, or a glycated hemoglobin level ≥6.5%. Hypovitaminosis D was defined as a serum 25-hydroxyvitamin D [25(OH)D] level <30.0 ng/mL. Associations were estimated using multiple logistic regression models.

The mean age of the participants was 41.3 ± 14.9 years; 56.8% were women, and 90% belonged to the Tupiniquim ethnic group. After adjusting for confounders, serum 25(OH)D levels were inversely associated with T2DM. Each 1-ng/mL increase in 25(OH)D was associated with lower odds of T2DM (OR = 0.96; 95% CI: 0.94-0.98). Individuals with hypovitaminosis D had higher odds of T2DM than those with adequate vitamin D levels (OR = 1.77; 95% CI: 1.20-2.62).

Vitamin D deficiency was independently associated with the presence of T2DM. The high prevalence of hypovitaminosis D underscores the importance of screening strategies and considering supplementation protocols, even among Indigenous populations with high solar exposure.