The elderly are a well-established group at risk of vitamin D deficiency. However, a high prevalence of vitamin D deficiency has also been reported in young healthy adults across Europe. Despite this, the causes of vitamin D deficiency in younger age groups have not been well characterised. The aims of this study were 1) to determine the relationship between age and circulating 25(OH)D in healthy participants in a UK population and 2) to determine the causes of any difference in circulating 25(OH)D with age. We conducted a cross-sectional study of 112 healthy younger and older adult men and women (ages 16 to 42 and 55 to 77). Anthropometric measurements, diet diaries, sunlight exposure questionnaires and blood samples were collected from all participants. 25(OH)D3 half-life was measured using a low oral dose of a stable isotope of 25(OH)D3. More of the younger age group had serum 25(OH)D below 30 nmol/l than the older age group (67% vs 40%, P<0.01). Serum 25(OH)D (27.0 nmol/l [SD 19.6] vs. 45.3 nmol/l [SD 27.8], P<0.001) and measured free 25(OH)D (3.3ng/l [SD 1.54] vs. 4.37ng/l [SD 1.62], P<0.001) were lower in younger adults than in older adults. Dietary vitamin D intake was lower (2.64 μg/d [SD 1.64] vs. 3.86 μg/d [SD 3.03], P=0.04) and 25(OH)D3 half-life was shorter in younger adults (17.2 days [SD 3.44] vs. 18.7 days [SD 4.02], P=0.045) compared with older adults. Sunlight exposure did not differ between age groups. We conclude that there is a high prevalence of vitamin D deficiency in young healthy adults in the UK during the winter and this is likely due to lower dietary vitamin D intake and a shorter 25(OH)D half-life than in older adults.
Disclosure: The authors declared no competing interests. This report is independent research commissioned and funded by the Department of Health Policy Research Programme (The Value of 25 Hydroxyvitamin D as a Biomarker in Obesity, 024/0052). The views expressed in this publication are those of the author(s) and not necessarily those of the Department of Health.