A systems biology approach to studying the effect of increasing vitamin D intake through food fortification on 25OHD status, in different population groups.

Vitamin D deficiency is a major public health concern in the UK. As the natural sources of vitamin D in the UK are limited, supplementation or food fortification are possible strategies for achieving the dietary recommendations of 10 μg/d that will be introduced in 2016 for the whole population. However, there is controversy as to whether vitamin D2 and vitamin D3 are equally effective at raising vitamin D status (25OHD concentration). The primary and secondary aims of this PhD project were: to investigate the effects of both these forms of vitamin D independently on vitamin D status, markers of bone and cardiovascular health, and gene expression; as well as to examine whether common genetic variants affect response to either form of vitamin D. A cohort of 90 South Asian and 245 Caucasian women were recruited onto a randomised-controlled trial; the D2-D3 Study. Participants were given either 15 µg/d of vitamin D2, 15 µg/d of vitamin D3 or placebo, in fortified foods, for 12 weeks. At baseline, serum total 25OHD concentrations were significantly lower in the South Asian women (27.6 nmol/L) than the Caucasian women (60.3 nmol/L). In both the South Asian and Caucasian women, 25OHD concentrations significantly decreased in the placebo intervention (-5% and -15% respectively, p<0.001), and significantly increased in both the vitamin D2 (112% and 39% respectively, p<0.001) and the vitamin D3 interventions (243% and 72% respectively, p<0.001), with significantly greater increases seen in the vitamin D3 intervention (p<0.001). In the vitamin D3 groups, parathyroid hormone (PTH) concentrations decreased in the South Asian women (p