Daily, seasonal, and latitudinal variations in solar ultraviolet A and B radiation in relation to vitamin D production and risk for skin cancer.
Int J Dermatol. 2015 Nov 6. doi: 10.1111/ijd.13065. [Epub ahead of print]
Grigalavicius M1, Moan J1,2, Dahlback A2, Juzeniene A1.
1 Department of Radiation Biology, Institute for Cancer Research, Norwegian Radium Hospital, Oslo University Hospital, Oslo, Norway.
2 Institute of Physics, University of Oslo, Oslo, Norway.
BACKGROUND:
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.
OBJECTIVES:
This paper focuses on the latitude dependency of UVB, UVA, vitamin D production, and skin cancer risk in Caucasians.
METHODS:
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.
RESULTS:
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.
CONCLUSIONS:
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.
© 2015 The International Society of Dermatology.
PMID: 26547141
See also VitaminDWiki
- Overview Suntan, melanoma and vitamin D
- Melanoma risk 2X to 4X higher if Vitamin D receptor genes had morphed – March 2014 Note: not SCC
- Nonmelanoma skin cancer IS associated with increased risk of other cancers – March 2014 lower levle of vitamin D in all cases
- Most German skin cancer doctors recommend both sunscreen and vitamin D – Dec 2012
- Sunlight, Vitamin D and Skin Cancer – 2nd edition Aug 2013
A chapters costs $20. Several of the chapters are written by authors of study on this page
lots of charts from the book on VitaminDWiki