Vitamin D supplementation, the metabolic syndrome and oxidative stress in obese children.

Background: Previous studies suggest that vitamin D may play a role in cardiovascular and metabolic health. Oxidative stress has also been implicated in the development of cardiovascular disease. Evidence suggests that vitamin D deficiency may contribute to the occurrence of oxidative stress. This study aimed to determine whether treatment and correction of vitamin D deficiency in obese children led to changes in their metabolic profile, independent of changes in adiposity. In addition, we aimed to determine whether vitamin D deficiency and oxidative stress are causally related in obese children.

Methods: In the retrospective arm, chart review identified 32 obese children who experienced normalization of vitamin D deficiency or insufficiency with vitamin D supplementation. We then correlated laboratory and anthropometric data with vitamin D levels. In the prospective arm of the study, urinary 8-isoprostane and hydrogen peroxide were measured before and after correction of vitamin D deficiency/insufficiency and correlated to vitamin D levels in seven patients.

Results: In our predominantly Hispanic population of obese children in an urban setting, we demonstrated a cause-effect relationship between vitamin D deficiency and oxidative stress. In contrast, we found no association between vitamin D status, adiposity, and markers of insulin sensitivity, nor any effect of vitamin D treatment on the same parameters.

Conclusions: These discordant findings suggest a differential effect of vitamin D on cardiovascular risk factors such as oxidative stress and insulin resistance. To confirm these findings, further prospective studies with larger sample size and longer follow-up are warranted.