Factors influencing the vitamin D status of 10-year-old urban South African children

Objective: Assessment of vitamin D status in a cohort of healthy 10-year-old urban children and the factors that influence vitamin D status in these children. Design: A cross-sectional study. Blood samples were collected across four seasons of the year for the biochemical determination of serum 25-hydroxyvitamin D [25(OH)D]. Anthropometric measurements (height and weight), BMI and total fat and lean mass (determined by the dual energy X-ray absorptiometry) were measured. 25(OH)D concentrations were assessed by chemiluminescent assay. Setting: Study of children in the Greater Johannesburg area of South Africa who form the Bone Health sub-cohort of the longitudinal Birth to Twenty cohort. Subjects: Three hundred and eighty-five children who form the Bone Health sub-cohort of the longitudinal Birth to Twenty cohort. Results: White children had significantly higher 25(OH)D than their black peers (120.0 (SD 36.6) nmol/l v. 93.3 (SD 34.0) nmol/l, respectively). Seasonal variations in 25(OH)D levels were found only in white children, with 25(OH)I) levels being significantly higher in white than in black children during the autumn and summer months. In multiple regression analysis, season, ethnicity, sex and total fat mass were the factors found to have an influence on 25(OH)D. Vitamin D deficiency (7%) and insufficiency (19%) were uncommon among the 10-year-old children. Conclusions: Vitamin D supplementation or fortification is not warranted in healthy children living in Johannesburg. However, further studies need to confirm this in other regions of the country, especially in those living further south and with less sunshine during the winter months.