The questionable effectiveness of sunscreen

Adam E Handel a b, Sreeram V Ramagopalan a b

In their Seminar (Feb 20, p 673),1 Vishal Madan and colleagues highlight a rising incidence of non-melanoma skin cancer (NMSC) in several countries. The incidence of NMSC also seems to be increasing in the USA.2 This increase is the reverse of what is expected given the continued increased purchase of sunscreen per head in the USA and UK since the 1990s (figure).3, 4

Figure Full-size image (26K) Download to PowerPoint

Purchase of sunscreen products by volume per head over time in the USA and UK3, 4

The contradiction suggests that increased population exposure to sunscreen does not translate into a reduced risk of skin cancers. This finding is particularly important for public health measures to prevent NMSC (and melanoma). It could be that sunscreens are being improperly used, or that they are ineffective in the prevention of skin cancer, or that other factors not related to ultraviolet (UV) light are leading to an increased risk of NMSC and melanoma.1

Sunscreen has the potential to have negative effects since synthesis of vitamin D relies on UVB radiation.5 Since vitamin D deficiency has been linked to the pathogenesis of many diseases,5 it is crucial that the effectiveness of sunscreens and their use are thoroughly investigated.

We declare that we have no conflicts of interest.

References

1 Madan V, Lear JT, Szeimies RM. Non-melanoma skin cancer. Lancet 2010; 375: 673-685. Summary | Full Text | PDF(932KB) |CrossRef | PubMed

2 Stern RS. The mysteries of geographic variability in nonmelanoma skin cancer incidence. Arch Dermatol 1999; 135: 843-844.CrossRef | PubMed

3 Euromonitor. Cosmetics and toiletries: sun care. http://www.euromonitor.com/Sun_Care. (accessed May 25, 2010).

4 United Nations. World population prospects: the 2008 revision. http://esa.un.org/unpd/wpp2008/index.htm. (accessed May 25, 2010).

5 Holick MF. Vitamin D deficiency. N Engl J Med 2007; 357: 266-281. CrossRef | PubMed

a Wellcome Trust Centre for Human Genetics, University of Oxford, Oxford OX3 7BN, UK

b Department of Clinical Neurology, University of Oxford, John Radcliffe Hospital, Oxford, UK

Lighting the way to better health: vitamin D

17th July 2010

The Lancet

The public health message is compellingly simple: avoid the sun to prevent melanoma and other forms of skin cancer. Unfortunately, exposure to sunlight is the mainstay of vitamin D synthesis, and vitamin D deficiency causes rickets and osteomalacia, contributes to osteoporosis, and has been associated with many other disorders, including diabetes, cancer, and cardiovascular disease.

Ultraviolet B radiation produces 90% of vitamin D in human beings; only a very small proportion can be obtained through diet. However, at high latitudes, levels of sunlight in winter are often so low that vitamin D insufficiency is common. Avoidance of the sun’s rays by covering up or use of sunscreen can compound this problem, and is thought to have contributed to a recent increase in metabolic bone disease. Cancer Research UK recognises the need to balance skin cancer prevention with generation of adequate vitamin D, but specified that “the skin efficiently produces vitamin D at levels of sun exposure below those that cause sunburn…when it comes to sun exposure, little and often is best”. Australia’s SunSmart guidelines underwent a revision to reflect this balance in 2006—07.

A major concern is that people might seek prolonged sun exposure without protection to boost vitamin D synthesis. Indeed, the American Academy of Dermatology argues that the risks of sun exposure outweigh the benefits, advocating instead for dietary supplementation as a safe source of vitamin D. A report published in the British Journal of Nutrition emphasises that in the UK, a unified approach to vitamin D supplementation is needed to address deficiency in pregnant women and avoid life-threatening complications for their babies.

Despite the simmering debate about sun exposure surrounding vitamin D, the SUNLIGHT consortium’s genome-wide association study, published in The Lancettoday, should add to our understanding of the genetic basis of interindividual variability in the synthesis of vitamin D. These findings could eventually help to identify who is most at risk of vitamin D insufficiency and related diseases. Until such potential applications come to the fore, the message about sun exposure has to be sensibly moderate. Enjoy the summer sun, with caution.

Source : The lancet

http://www.thelancet.com/journals/lancet/article/PIIS0140-6736(10)61094-X/fulltext?elsca1=TL-160710&elsca2=email&elsca3=segment