Although overexposure to solar ultraviolet radiation (UVR) is responsible for cutaneous
melanoma and epithelial
skin cancer and can cause negative health effects such as
sunburn, a "little and often" exposure regime is often suggested to produce naturally recommended
vitamin D levels, being essential for skeletal health. This study aimed to quantify solar UV doses needed to trigger 1000 International Units (IU)
vitamin D doses and, at the same time, producing
sunburn in Switzerland. Solar UV
erythema irradiance (in mW/m2) measured at four meteorological stations in Switzerland for the period 2005-2017 were used to evaluate effective solar UV radiation producing 1000 IU
vitamin D doses in skin phototype II and III individuals. Daily solar UV exposure durations (in minutes) needed to produce
vitamin D with limited
sunburn risk were estimated while considering mean
vitamin D food intake of the Swiss population and seasonal skin coverage. In summer and spring, with 22% of uncovered skin, 1000 IU
vitamin D doses are synthesized in 10-15 min of sun exposure for adults. Exposure durations between
erythema risk and 1000 IU
vitamin D production vary between 9 and 46 min. In winter and autumn, the recommended
vitamin D production without
sunburn risks often unachievable, since up to 6.5 h of sun exposure might be necessary considering 8-10% of uncovered skin surface. The
vitamin D food intake only represented 10% of the recommended
vitamin D production and remained unchanged throughout the year. These findings might clarify why
vitamin D deficiency is common in Switzerland. Moreover, exposure durations between recommended
vitamin D and increased
sunburn risk might only differ by few minutes. Without additional oral
vitamin D supplementation, daily doses of
vitamin D (1000 IU) are not reachable in autumn and winter months in Switzerland.