Abstract
BACKGROUND: Vitamin D deficiency is becoming a worldwide public health concern as it increases the risk of many diseases and disorders. Little is known about the health outcomes of such deficiency in the South Asian population, in which it is more pronounced. The aim of this thesis was therefore to investigate the ethnic differences between South Asians and Caucasians with regard to the effect of vitamin D status on osteoporosis and cardiovascular disease risk. Furthermore, the study aimed to determine the extent of the problem and the genetic or social reasons behind it. METHODS: The research involved three sub-projects; the first of which undertook further analysis of the data from the original Vitamin D, Food Intake, Nutrition and Exposure to Sunlight in Southern England (D-FINES) study. Subjects from D-FINES were then re- invited to take part in the second part of this research, which measured volumetric bone density of the tibia and radius as using (pQCT)estimates of bone health. General health and biomarkers of cardiovascular disease and osteoporosis were assessed by standard clinical biochemical blood assays. The final stage utilised an interventional study design to test the efficiency of vitamin D production in both ethnic groups following controlled exposure to ultraviolet (UV) radiation. RESULTS: In general, South Asian women had significantly lower vitamin D status, HDL cholesterol and insulin sensitivity; significant higher BMI, insulin level, insulin resistance and beta cell function compared to Caucasian women. All of these undesirable biochemical indicators put South Asian women at higher risk of cardiovascular disease. South Asian women also had lower bone areas in all sites measured; and lower cortical bone thickness and volumetric bone density at some sites of tibial bone. All of these bone parameters indicate lower bone strength among South Asian women compared to Caucasian women; leading to a higher risk of osteoporosis long- term. Despite consistently lower vitamin D levels in South Asian women they were shown to synthesise vitamin D just as efficiently as Caucasians when exposed to the same dose of UV. Interestingly, the baseline level of vitamin D rather than ethnicity influenced the amount of UV needed to reach equal serum concentrations. This novel finding indicated no effect of skin tone on the production of vitamin D and identified that length of exposure was the critical factor. Inferences made from data collected on UV skin exposure behaviour of the two groups suggested that the main reason for predominant vitamin D deficiency in south Asians is their tendency to avoid sunlight for fear of tanning. CONCLUSION: More research and public health messages to the South Asian population are urgently required to reduce cardiovascular and osteoporosis risk factors. This could be achieved by a number of ways 1. Encouraging more widespread use of vitamin supplements 2. Educating on the health benefits of safe UV exposure to increase their vitamin D status. 3. Encouraging a vitamin D rich diet Furthermore the association between vitamin D, bone health indices and lipid profiles warrant additional research in both groups.