No Relationship Between Vitamin D Status and Insulin Resistance in a Group of High School Students

Objective: To investigate the effects of vitamin D deficiency on both insulin resistance and risk of metabolic syndrome in children.

Methods: The study group consisted of 301 children and adolescents with a mean age of 14.2 ± 1.8 years. Serum 25-hydroxyvitamin D [25(OH)D] levels and insulin resistance indices were evaluated. According to serum 25(OH)D levels, the subjects were classified in 3 groups. Those with levels ≤ 10 ng/mL were labeled as the vitamin D deficient group (group A), those with levels of 10-20 ng/mL as the vitamin D insufficient group (group B) and those with ≥ 20 ng/mL as having normal vitamin D levels (group C). Metabolic syndrome was defined according to the International Diabetes Federation consensus. The participants with and without metabolic syndrome were compared in terms of 25(OH)D levels.

Results: Mean 25(OH)D level of the total group was 18.2 ± 9.3 (2.8-72.0) ng/mL. Distribution of individuals according to their vitamin D levels showed that 11.6% were in group A, 53.5% in group B, and 34.9% in group C. The proportions of boys and girls in these categories were 22.9% and 77.1% in group A, 36.6% and 63.4% in group B, 54.3% and 45.7% in group C, respectively. There were no significant differences in 25(OH)D levels in the individuals with and without impaired fasting glucose or impaired glucose tolerance. No relationship was observed between insulin resistance/sensitivity indices and vitamin D status (p > 0.05). Metabolic syndrome was diagnosed in 12.3% (n = 37) of the children. There was also no difference in mean 25(OH)D levels between individuals who had and those who did not have the metabolic syndrome.

Conclusion: In our study, no correlations were found between insulin measurements during oral glucose tolerance test and vitamin D deficiency. Nonetheless, more extended studies including vitamin D supplementation and evaluating insulin sensitivity via clamp technique are needed to further elucidate this relationship.