Calculations of the human vitamin D exposure from UV spectral measurements at three European stations.

The health benefits of solar UVB and vitamin D in reducing the risk of cancer and several other diseases have been well documented in recent years. In this study, quality-checked spectral UV irradiance measurements from three European stations (Jokioinen, Finland; Bilthoven, The Netherlands; and Thessaloniki, Greece) are used and the vitamin D effective dose (VDED) is calculated. The maximum average daily VDED is measured during the second half of June and it is up to 250 times higher than the corresponding winter minimum value. At each site, a polynomial fit between the VDED and the erythemal dose rates is proposed. The average VDED rates at local noon exceed a detection threshold value for the cutaneous production of vitamin D at Thessaloniki and Bilthoven throughout the year. The proposed standard vitamin dose cannot be attained, even for skin types I-III and exposure time of 60 minutes around local noon, under physiological atmospheric conditions at Bilthoven and Jokioinen during 3 and 4 months respectively. The daily VDED values, using the CIE action spectrum, are higher from 2% and 8% during summer and winter respectively at all sites, compared with those derived by the action spectrum proposed by MacLaughlin et al. (Science, 1982, 216, 1001-1003). These differences are comparable with the uncertainty of spectral measurements.