Dietary intake and factors affecting vitamin D status of Middle Eastern people in the UK

Abstract

Vitamin D is derived through the action of solar ultraviolet B radiation on skin and from a limited number of natural food sources, fortified foods and supplements. It is well known that vitamin D plays an active role for calcium and phosphorus absorption but there is also growing evidence of an association between vitamin D insufficiency and various chronic diseases. Middle Eastern populations are known to be at risk of vitamin D deficiency due to a diet low in vitamin D and low sunshine exposure. Obesity is also a risk factor since vitamin D is sequestered in body fat. This thesis examined dietary intake of vitamin D, obesity and other risk factors for deficiency in Middle Eastern people in the UK. A questionnaire based survey was undertaken with 242 Middle Eastern respondents. A total of 85% of the sample was estimated to have a vitamin D intake <5 µg/d. Other risk factors for vitamin D insufficiency included covering skin from sunlight (84% females); low use of supplements (18.5%) and being overweight or obese (49% males and 44% females). Vitamin D intake was lowest in those with primary (1.8 µg/d) and secondary school (2.1 µg/d) education compared to higher education (3.6 µg/d). The survey was followed by dietary assessment of 28 Iraqi adults using repeat 24 hour recalls. The results concurred with the survey: mean intake of vitamin D was (3.2±4.4 µg/d) and 78.5% were overweight or obese. Finally, overweight participants were recruited to observe the effect of fat loss on vitamin D status. Serum 25(OH)D concentrations was measured in Middle Eastern (n=12) and Caucasian adults (n=24). Firstly seasonal changes were observed between October and January (with no weight loss). Then participants were advised on weight reduction to observe the effect of fat loss on serum 25(OH)D. Vitamin D deficiency (<25 nmol/l) was observed in 67% of the Middle Eastern group in October increasing to 92% in January. Of the 36 participants, only 17 lost ≥1kg of fat mass between January and April. No difference was found in serum 25(OH)D between those that lost fat mass and those that did not, and no correlation was found between the amount of fat lost and change in 25(OH)D. In the total sample, there was a negative association between serum 25(OH)D and waist circumference and waist-hip ratio, but no correlation was found between 25(OH)D and fat mass, thus indicating a relationship with visceral fat stores rather than total fat mass.