Health risks and benefits of UV radiation: Assessing exposure times related to vitamin D3 synthesis alongside the potential risk of sunburn in northern mid-latitudes.

In this research, the duration of exposure of unprotected skin required for the synthesis of 1000 IU of vitamin D3 (1000D3), along with the associated risk of erythema, was examined for Novi Sad (45.33° N, 19.85° E, 84 m asl) and Kopaonik (43.28° N, 20.80° E, 1710 m asl) (Serbia) in the period 2004-2020. A novel model for estimating hourly ultraviolet radiation doses from daily values was proposed. The focus was on data around local noon (10:00 and 15:00 h CET), skin types II and III, and four age groups (0-21, 22-40, 41-59, 60+). The analysis showed that from April to September, most individuals can expose their skin to sunlight enough to produce 1000D3 without exceeding the erythema threshold. Nevertheless, during February, March, October, and November, most age groups have a greater risk of erythema prior to achieving 1000D3. However, in the winter months, the exposure required to obtain 1000D3 frequently exceeds the level at which erythema can develop. Moreover, during January and December, even spending up to five hours in the sun is insufficient for most individuals to reach the 1000D3. It is also noted that levels of hourly erythema and vitamin D3 doses are higher in Kopaonik than in Novi Sad, likely due to the higher elevation. Therefore, the exposure time for causing erythema is shorter in Kopaonik. However, due to a smaller body exposure area, the exposure time required to achieve the 1000D3 is longer in Kopaonik than in Novi Sad, while sub-erythemal vitamin D3 synthesis windows are very close, except during winter.