Evaluation of fall Sun Exposure Score in predicting vitamin D status in young Canadian adults, and the influence of ancestry

https://doi.org/10.1016/j.jphotobiol.2015.02.007Get rights and content

Highlights

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    There is a need for simple inexpensive screening tools for vitamin D status.

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    Ancestry was the strongest predictor of vitamin D status in our study population.

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    The majority of our East and South Asian population was vitamin D insufficient.

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    Inquiry of ancestry may be a useful screen for estimating vitamin D status.

Abstract

Query of sun-related habits or ancestry could help screen for risk of vitamin D insufficiency (serum 25-hydroxyvitamin D < 75 nmol/L). We evaluated the association between Sun Exposure Score (calculated from recall of Time Exposed to Sun and Skin Exposed to Sun in the previous week), demographics and anthropometrics (including self-reported ancestry and skin melanin reflectometry), and serum 25(OH)D levels in healthy young Canadian adults in the Greater Toronto Area (GTA; 43°N) during fall. 310 adults (67% female) of European, East Asian, and South Asian ancestries were evaluated. The median (interquartile range) 25(OH)D level was 49.7 nmol/L (36.7–70.3) and 80% of participants were vitamin D insufficient. The vast majority of those of East and South Asian ancestry were vitamin D insufficient (91% and 97%, respectively), as were 55% of those of European ancestry. Sun Exposure Score and 25(OH)D concentrations were not associated after accounting for confounders. A multivariable model showed ancestry, recent summer sun exposure, sex, melanin, vitamin D intake, age and year of study significantly predicted 25(OH)D concentration; ancestry was the strongest independent predictor (adjusted R2 = 43%). Although Sun Exposure Score was not a significant predictor of serum 25(OH)D levels, inquiry of ancestry has potential use in screening for vitamin D insufficiency.

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.

Section snippets

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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