Vitamin DEED Study – Determinants of vitamin D status in women: the role of the environmental factors, ethnicity/skin type and diet

Despite the essential role of vitamin D in calcium homeostasis, vitamin D deficiency is prevalent worldwide (2). This thesis aimed to determine levels of vitamin D deficiency and strengthen the evidence around the impact of skin type, diet and sun exposure on vitamin D status and associated musculoskeletal outcomes at varying latitudes. A systematic literature review characterised the current vitamin D status of the African-Caribbean (AfC) population living at varying latitudes. Meta-analysis of the data extracted found this population to have sufficient (>50 nmol/L) 25(OH)D levels at 67.8 nmol/L, 95% CI (57.9, 7.6) but poor dietary intake of vitamin D at only 3.0μg/day, 95% CI (1.67,4.31). However, at high latitudes, the mean 25(OH)D was found to be insufficient at 40.9nmol/L, 95% CI (28.1, 53.7), confirming the need for further research at high latitudes. The author built on this evidence review with a secondary analysis of the UK Biobank cohort to investigate the extent of vitamin D deficiency and dietary intakes of the AfC population in the largest sample of AfC individuals to date (n=4046). Over one third of this population were deficient (<25nmol/L), 47.1% were insufficient (25-50nmol/L) and 15.9% were sufficient (>50nmol/L). Median (IQR) 25(OH)D was insufficient at 30.0 (20.9) nmol/L. Finally, a cross-country design was adopted to explore the impact of, skin type, diet, sun exposure and lifestyle factors on the vitamin D status of healthy females living in three different countries at varying latitudes (Wollongong, Australia: 34.42° S, Surrey, United Kingdom (UK): 51.24° N, and Sao Paulo, Brazil: 23.55° S). Two hundred and twenty females were included in the study of which 6% were vitamin D deficient (<25nmol/L), 15.1% were vitamin D insufficient (<50nmol/L), 48.2% were vitamin D sufficient and 30.3% had optimal vitamin D concentrations. Mean vitamin D intake was 3.4 ± 2.8μg/day for all participants, with 92% of participants having inadequate vitamin D intakes. Overall, these findings show high levels of vitamin D deficiency at high latitudes. Country specific sunlight exposure recommendations are required, that take into environmental and personal factors, as well education around sources of dietary vitamin D.