Evaluation of fall Sun Exposure Score in predicting vitamin D status in young Canadian adults, and the influence of ancestry
Introduction
Vitamin D insufficiency is associated with increased risk of and poorer outcomes in autoimmune, cardiovascular and malignant disease. Although vitamin D can be obtained through diet or supplements, our main source is solar ultraviolet (UV)-B mediated cutaneous synthesis.
In Canada, seasonal fluctuations in solar UVB and, thus, resultant production of vitamin D limit the utility of serum 25-hydroxyvitamin D [25(OH)D] tests [1]. A brief questionnaire to screen sun exposure could provide a cost and time-effective strategy to guide individual vitamin D supplementation practices. In a previous study of healthy Italian adults, a 7-day sun exposure questionnaire predicted serum 25(OH)D concentrations in the summer [2]. However, the utility of this questionnaire in estimating vitamin D status in other settings is unknown. We therefore sought to evaluate the value of the Sun Exposure Score in predicting fall 25(OH)D concentrations in ancestrally diverse young Canadian adults, and to ascertain the strongest predictors of 25(OH)D concentrations, including sun exposure, self-reported ancestry, skin pigmentation and vitamin D intake.
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Study population and recruitment
Recruitment, study eligibility and most aspects of data collection have been previously described [1]. Participants between the ages of 18 and 35 years were recruited at the University of Toronto Mississauga campus (Toronto, Ontario, Canada; 43°N) in fall 2007 and 2008. Exclusion criteria included kidney or liver disease, a diagnosis potentially affecting vitamin D metabolism or absorption, such as osteomalacia, osteopenia, or Crohn’s disease, use of medications affecting vitamin D metabolism
Participant characteristics
A total of 310 participants from the three main ancestral groups completed a sun exposure questionnaire and were included in subsequent analyses. Participant characteristics are displayed in Table 1.
Sun Exposure Score and 25(OH)D concentrations
The unadjusted correlation between Sun Exposure Score and 25(OH)D concentration was weak although statistically significant (Pearson’s correlation = 0.19, p = 0.01; Fig. 2). Using multiple linear regression analyses, several variables were identified as potential confounders of the association between
Discussion
Fall Sun Exposure Scores were not correlated with serum 25(OH)D concentrations after adjustment for confounders, demonstrating that in this population, using the Sun Exposure Score in the fall is of limited use in predicting vitamin D status. Another study using the same Sun Exposure Score [2] demonstrated a stronger correlation between Sun Exposure Score and 25(OH)D concentrations during summer in an ancestrally homogeneous Italian adult population. The weaker correlation in the present study
Conclusions
Fall Sun Exposure Score was not associated with 25(OH)D concentrations. Ancestry was a relatively strong predictor of 25(OH)D concentrations and vitamin D sufficiency status, with the vast majority of individuals of East and South Asian ancestry being vitamin D insufficient (91% and 97%), as compared to just over half of those of European ancestry (55%). Thus, query of ancestry could be used as a possible screen to identify those at risk of vitamin D insufficiency, as it is a better predictor
Acknowledgements
This work was supported by an endMS Summer Research Studentship (L.S.), a Multiple Sclerosis Society of Canada Doctoral Studentship (S.M.), an Early Research Award from the Government of Ontario and the Natural Sciences and Engineering Research Council of Canada (E.J.P.), and a Hospital for Sick Children Restracomp Fellowship (H.E.H.).
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