In order to investigate the influence of solar radiation on vitamin D status and its association with different health outcomes in population based studies, appropriate estimates of the subjects’ UV radiation exposure are needed. This unique study describes a method that estimates the daily number of vitamin D effective hours (VD-hours) at arbitrary ground locations throughout the period 1957–2002. The method is particularly suited for large-scale prospective epidemiological studies with questionnaire-based information on sun exposure, and where blood measures of vitamin D status are not available.
The model takes total cloud cover fraction and total ozone column at noon as input from the ERA-40 data series (i.e. the 40 + year European Centre for Medium-Range Weather Forecasts Re-Analysis archive). By comparing the model results against high accuracy measurements at two different locations in Norway, we found the method for estimating the number of VD-hours to be accurate within 2.5 ± 7% or better for moderate solar zenith angles (< 65°).
For higher solar zenith angles (> 65°) the results are more variable, but the contribution to a population’s vitamin D level from solar radiation when the sun is this low in the sky is rather small. The program code to compute VD-hours from ERA–40 files is written in Perl (v 5.8.7) and may be obtained free of charge by contacting corresponding author.
Edvardsen, K., Engelsen, O. and Brustad, M., 2009. Duration of vitamin D synthesis from weather model data for use in prospective epidemiological studies. International journal of biometeorology, 53(5), pp.451-459.
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