Vitamin D levels in prepubertal children in Southern Tasmania: prevalence and determinants

Objective: To describe the prevalence and determinants of 25-hydroxy D 3 (25(OH)D) in children. Design: Cross-sectional study. Setting: Southern Tasmania between June and November 1997. Subjects: Two hundred and one 8-y old male and female children taking part in a cohort study whose principal endpoints were blood pressure and high-density lipoprotein (HDL) cholesterol. Results: The mean 25(OH)D level was 79 nmol/l (s.d. 29.5, median 73, range 12-222). Boys had higher levels than girls (82.1 vs 72.8 nmol/l, P = 0.02). 25(OH)D was associated with sunlight exposure in winter school holidays (r = 0.20, P = 0.005) and winter weekends (r = 0.16, P = 0.02), the month after school holidays (87.5 vs 69.5 nmol, P < 0.0001) and body mass index (r = -0.23, P = 0.001). Dietary intake of vitamin D was low (mean 40 IU/day, range 5.2-384) and was not associated with 25(OH)D levels (r = 0.01, P = 0.91). Variation in skin melanin density was weakly associated with 25(OH)D (r = 0.09, P = 0.19). Conclusions: Sunlight is the major determinant of vitamin D stores in our population. Neither variation in skin type within Caucasians nor diet modified this association to any significant extent. Extrapolation of these findings to sunlight bone mass associations in a very similar population suggests that a minimum level of around 50 nmol/l in the population is required for optimal bone development in prepubertal children but this needs to be confirmed with further controlled trials of vitamin D supplementation and bone mass.