Vitamin D Status, Latitude and their Associations with Some Health Parameters in Children: National Food and Nutrition Surveillance

BACKGROUND: Recent data indicate a role for vitamin D in many health aspects including anthropometric measures and blood lipid profiles. Dermal vitamin D synthesis may be influenced by latitude. However, the contribution of latitude in vitamin D status and its association with anthropometric and blood lipid measures in Iranian children have not been studied to date. METHODS: We used data from the National Food and Nutritional Surveillance Program. In total, 667 apparently healthy children aged 5-18 years were randomly selected from six provinces of Iran with different latitudes, from 29 to 37°. Weight, height, circulating 25-hydroxycalciferol; calcidiol [25(OH)D] and blood lipids were measured. RESULTS: In total, 16.7 and 4.1% of children were overweight or obese, respectively. The mean 25(OH)D concentration was 27.3 ± 17.6 nmol/l (95% confidence interval: 26.0-28.7 nmol/l). Over 93% of all children had suboptimal circulating calcidiol concentrations. Undesirable status of vitamin D, serum triglyceride and low-density lipoprotein were all more prevalent in children living in regions >33° latitude than those in <33°, significantly. There was no significant difference in duration of sun exposure between children living in latitudes below and above 33° (p = 0.093). In multivariate regression model, sex, latitude, body mass index for age z-score and sun exposure duration were independently related to 25(OH)D concentrations, but age was not. CONCLUSION: Despite significant association of latitude and vitamin D status, hypovitaminosis D is prevalent across latitude gradient in Iranian children. Our findings warrant immediate sustainable nutritional intervention, including supplementation, to protect children from hypovitaminosis D irrespective of the latitude of their residence.