Why is it so hard to gain enough Vitamin D by solar exposure in the European winter?
Earth and related Environmental sciences
Hemispherical UV Differences
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UV exposure, which is the main source for a sufficient level of vitamin D in the human body, is found to be up to a factor of 7 lower in Northern Germany (52° N) in the winter months compared to UV levels in the central region of New Zealand's South Island (45° S). When corrected for the influence of solar zenith angle, the vitamin D-weighted exposure is still a factor of 2 higher in the southern hemisphere at the corresponding latitude. The major part of the difference can be attributed to differences in cloudiness, and a minor part to total ozone and aerosols. Data from several stations in Europe show a high variability due to cloudiness differences between the stations and between different years, but they also show that the differences are not restricted to individual sites and may characterize a northern versus southern hemisphere contrast. Wintertime erythemally-weighted irradiance is also found to be much higher in New Zealand than in Europe. Whereas on a monthly average clouds weaken the UV irradiation by up to 25 % for most locations in New Zealand, the reduction is usually up to 50 % in central Europe in winter.
CitationSeckmeyer, G.; Mustert, C.; Schrempf, M.; McKenzie, R.; Liley, B.; Kotkamp, M.; Bais, A.; Gillotay, D.; Slaper, H.; Siani, A.-M.; Smedley, A.; Webb, A. (2018). Why is it so hard to gain enough Vitamin D by solar exposure in the European winter?. , Meteorologische Zeitschrift, Vol. 27, Issue 3, 223-233, DOI: 10.1127/metz/2018/0855.