 At baseline and 6 months, dual-energy x-ray absorptiometry DXA will be used to quantify total body and regional fat masses. This will be done to help explain any differences in response to vitamin D intakes since more central deposition of adipose tissue relates to vitamin D status in adults 15. DXA will also be used to measure changes in BMC and BMD over the 6 month period to explore their relationship to vitamin D status. Measurements will be taken using a Hologic 4500A clinical densitometer. Whole body, lumbar spine L1-4 and forearm scans will be undertaken to measure BMC and BMD, children will wear standardized clothing pyjama bottoms and T-shirt. The whole body scan technique also provides total body fat, but does not distinguish subcutaneous from visceral fat depots. Abdominal adipose will be estimated using sub-region analysis of the full torso and the between the last rib and the iliac crests. Total body fat kg and and trunk fat kg values are available from the DXA software. Although DXA measures of trunk fat mass reflect adipose tissue in subcutaneous and visceral depots, DXA-derived measures agree well with CT in women 16. 