Title: Vitamin D photosynthesis: Interactions with melanin and UVR spectrum
Funder: Department of Health (England)

Abstract: Background Solar UVR, especially UVB (~295-320nm), causes skin cancer, especially in fair-skinned people, but UVB is also the main factor in maintaining vitamin D status which is important for bone health. However, there are increasing reports of other health benefits of vitamin D. Vitamin D status is often “insufficient” in temperate climates, especially in winter, but surprisingly, “insufficiency” is also prevalent in sunny climates with high levels of ambient UVB (Kimlin et al, 2007; Lips, 2010; Vu et al, 2011). This is hard to explain given that low dose UVB exposures over small body surfaces are widely claimed to be sufficient. One in vitro study has suggested that vitamin D may be degraded by sunlight, especially UVA2 (320-340nm) (Webb et al, 1989). An action spectrum for previtamin D production in the skin (MacLaughlin et al, 1982; CIE, 2006) is widely used for risk benefit calculations, but the validity of this spectrum has been queried (McKenzie et al, 2009; Norval et al, 2010). An action spectrum cannot be used when spectral interaction leads to degradation of end product. This has never been assessed in vivo. People with naturally pigmented skins typically have poor vitamin D status (Harris et al, 1998; Gozdzik et al, 2008; Hannan et al, 2008; Vanlint et al, 2011; Macdonald et al, 2011), and rickets has been reported in the UK Asian community. It is widely assumed that melanin prevents vitamin D production, but the interaction of melanin and vitamin D photosynthesis is unclear, with contradictory data from the few laboratory studies that have been done (Springbett et al, 2010). Thus, the assumption that melanin protects against vitamin D synthesis needs to be rigorously tested. Aims: To study Work Package A: The relationship between skin melanin content and vitamin D photosynthesis. Does melanin inhibit vitamin D synthesis? Work Package B: Possible spectral interactions of UVB and UVA in vitamin D synthesis. Does UVA degrade UVB-induced synthesis of vitamin D in the skin? Research plan and methods Normal healthy male and female volunteers (young adults) of different skin types will be recruited and vitamin D status (serum 25(OH)D) determined by mass spectrometry. Work Package A: white- and dark-skinned people with similar baseline 25(OH)D levels will be exposed to whole body solar simulated radiation (SSR) protocols that we know enhance 25(OH)D in those with white skin. Pigmentation will be quantitatively assessed. Work Package B: whole body UVB exposure followed by whole body UVA exposure, with appropriate controls, in fair-skinned people. Research team The PI will be Prof. Antony Young who has considerable experience in human skin photobiology. He is currently working on vitamin D as part of the EC ICEPURE project (www.icepure.eu). A post-doctoral research associate (RA) will be appointed. The RA will be responsible for the day-to-day running of the project. If successful, this project would have a 5 month overlap with the ICEPURE project, conferring the advantage of its existing expertise and infrastructure. Impact Public health advice is based on avoiding UVR exposure, which may have an impact on vitamin D status and human health because UVR is the main source of vitamin D in the UK (Ashwell et al, 2010). This is especially important in people with pigmented skin. Overall, this proposal will provide a much better understanding of the photobiology of vitamin D production. It will add to our understanding of the risks versus the benefits of UVR and provide a basis for more informed public health advice on sun exposure (including its timing), diet and supplementation to maintain optimal vitamin D status.


Research activity codes: 1.1 NORMAL BIOLOGICAL DEVELOPMENT AND FUNCTIONING
Health categories: GENERIC HEALTH RELEVANCE