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IJE Advance Access published online on June 29, 2009
International Journal of Epidemiology, doi:10.1093/ije/dyp237
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Published by Oxford University Press on behalf of the International Epidemiological Association © The Author 2009; all rights reserved.

Predicting ambient ultraviolet from routine meteorological data; its potential use as an instrumental variable for vitamin D status in pregnancy in a longitudinal birth cohort in the UK

Adrian Sayers1,*, Kate Tilling2, Barbara J Boucher3, Kate Noonan4 and Jon H Tobias1

1Academic Rheumatology, Department of Clinical Science at North Bristol, University of Bristol, Bristol, UK.
2Department of Social Medicine, University of Bristol, Bristol, UK.
3Centre for Diabetes and Metabolic Medicine, Bart's and The London School of Medicine and Dentistry, Queen Mary University of London, London, UK.
4Department of Clinical Chemistry, Bart's and The Royal London NHS Trust, London, UK.

*Corresponding author. Academic Rheumatology, Avon Orthopaedic Centre, Southmead Hospital, Bristol BS10 5NB, UK. E-mail: adrian.sayers{at}bristol.ac.uk


  Abstract

Background Maternal vitamin D status in pregnancy has been postulated to have important effects on intrauterine development. UVB radiation is not commonly measured but is the prime determinant of circulating 25-hydroxyvitamin-D [25-(OH)D] and is highly dependent on regional weather including cloud cover, ozone and sunshine hours.

Methods Using linear regression we described the relationship between estimated ambient-erythemal ultraviolet (eUV) exposure in Oxford (1990–95) and total hours of sunshine and month in order to forecast eUV in nearby regions, whilst adjusting for regional variations in weather. The forecast was validated with empirical data collected from Cornwall and then predicted for the Avon region. Total 98-day prenatal ambient-eUV was then predicted in 355 expectant mothers in the Avon Longitudinal Study of Parents and Children (ALSPAC) cohort and its relationship with maternal vitamin D status was determined.

Results Estimated ambient-eUV was strongly associated with measured ambient-eUV (r2 = 0.989) with a near 1:1 prediction for the validation data set [β = 0.99, 95% confidence interval (CI) 0.913, 1.067 r2 = 0.980]; strong seasonal associations were observed between eUV in the last trimester of pregnancy and maternal serum 25-(OH)D concentrations (r2 = 0.40).

Conclusion This technique of prediction could be applied to existing cohorts allowing the relationship between maternal vitamin D status and the health of the offspring to be studied via instrumental variable analysis.

Keywords Epidemiology, maternal exposure, pregnancy, prenatal exposure delayed effects, seasons, ultraviolet rays, vitamin D, instrumental variable, ALSPAC

Accepted 26 May 2009


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