Grigalavicius Mantas, Moan Johan, Dahlback Arne, Juzeniene Asta
Department of Radiation Biology, Institute for Cancer Research, Norwegian Radium Hospital, Oslo University Hospital, Oslo, Norway.
Institute of Physics, University of Oslo, Oslo, Norway.
Int J Dermatol. 2016 Jan;55(1):e23-8. doi: 10.1111/ijd.13065. Epub 2015 Nov 6.
Solar ultraviolet (UV) radiation varies with latitude, time of day, and season. Both spectral UV composition and ambient UV dose lead to different health outcomes at different latitudes. Finding the optimal time for sun exposure, whereby the positive effects of UV exposure (vitamin D) are facilitated and the negative effects (skin cancer, photoimmunosuppression) avoided are the most important consideration in modern skin cancer prevention programs.
This paper focuses on the latitude dependency of UVB, UVA, vitamin D production, and skin cancer risk in Caucasians.
Biologically effective UVB (280-315 nm) and UVA (315-400 nm) doses were calculated using radiative transfer models with appropriate climatologic data for selected locations. Incidences of squamous cell carcinoma (SCC) and cutaneous melanoma (CM) were retrieved from cancer registries and published articles.
Annual doses of UVA radiation decrease much less with increasing latitude than annual doses of UVB. Incidences of CM also decrease less steeply with increasing latitude than incidences of SCC. As SCC is caused mainly by UVB, these observations support the assumption that UVA plays an important role in the development of CM. The variations in UVA (relevant to CM) and UVB (relevant to vitamin D production) over 1 day differ: the UVB : UVA ratio is maximal at noon.
The best way to obtain a given dose of vitamin D with minimal carcinogenic risk is through a non-burning exposure in the middle of the day, rather than in the afternoon or morning.
太阳紫外线（UV）辐射随纬度、一天中的时间和季节而变化。紫外线的光谱组成和环境紫外线剂量在不同纬度会导致不同的健康结果。在现代皮肤癌预防计划中，找到最佳的日晒时间最为重要，在此期间既能促进紫外线照射的积极作用（维生素D生成），又能避免其消极作用（皮肤癌、光免疫抑制）。
本文重点关注白种人中紫外线B（UVB）、紫外线A（UVA）、维生素D生成以及皮肤癌风险与纬度的关系。
利用辐射传输模型和选定地点的适当气候数据，计算生物有效UVB（280 - 315纳米）和UVA（315 - 400纳米）剂量。从癌症登记处和已发表的文章中检索鳞状细胞癌（SCC）和皮肤黑色素瘤（CM）的发病率。
随着纬度增加，UVA的年剂量下降幅度远小于UVB的年剂量。CM的发病率随纬度增加的下降幅度也比SCC的发病率小。由于SCC主要由UVB引起，这些观察结果支持UVA在CM发展中起重要作用的假设。一天中UVA（与CM相关）和UVB（与维生素D生成相关）的变化不同：UVB与UVA的比值在中午最大。
以最小致癌风险获得给定剂量维生素D的最佳方法是在中午进行非晒伤性暴露，而非在下午或上午。
