Friday September 19 2008
The dangers of sunbathing are well known
“There is no such thing as a ‘safe’ tan – especially from indoor tanning beds”, the Daily Mail reported today. It said that studies in the US found that tanning and cancer both start with DNA damage from ultraviolet (UV) rays. Achieving a safe tan may therefore be impossible. This story has been prompted by a review by Dr David Fisher, president of the Society of Melanoma Research, and his colleagues about the biological effects of UV radiation, its public health implications, and the commercial interests involved in the promotion of tanning.
As the authors of this thought-provoking article state, the evidence that UVR increases the risk of skin cancer is clear. Although adequate vitamin D is important for maintaining health (and may even reduce risk of some cancers), this does not mean that tanning is healthy. Most people should be able to obtain enough vitamin D from their diet and from sensible day-to-day indirect sunlight exposure. For those who are concerned about their vitamin D levels, a vitamin D supplement would be the best answer rather than resorting to excessive outdoor tanning or sunbeds.
Where did the story come from?
Dr Thanh-Nga Tran and colleagues from the department of Dermatology at the Massachusetts General Hospital wrote this “Perspective” piece. No funding sources for the article were reported. One of the authors reported providing consultancy for Novartis, Magen BioSciences, and Source MDx as possible conflicts of interest. The study was published in the (peer-reviewed) medical journal: Pigment Cell Melanoma Research.
What kind of scientific study was this?
This was a non-systematic narrative review that discussed the issues surrounding ultraviolet radiation (UVR) and human health. The authors summarised what is known about the effects that UVR can have on the body, such as the generation of vitamin D, tanning, inflammation, suppression of the immune system, and the development of cancer. It also discussed the social issues surrounding tanning – the public health implications, and the commercial interests in the promotion of tanning. The authors based these summaries on published literature, and gave their perspective on the issues surrounding tanning. Some of the key points of their article are summarised below.
What were the results of the study?
The authors report that despite public awareness campaigns about the dangers of tanning, revenue from the tanning industry is increasing, and is currently at about five million US dollars a year. In the US, about one million people use tanning facilities each day, and the majority of these users are white teenagers and women aged between 16 and 49 years. They say “it is widely felt that an effective lobbying effort by the tanning industry has contributed to continued growth and public use of the indoor tanning industry.” They then discuss various methods used to target teenagers through discounts and advertising, including promotion of the “health benefits” of UVR (particularly vitamin D production) “while attempting to suggest that linkage of UV to melanoma is less clear than previously assumed.” They say that the American Academy of Dermatology has requested stricter regulation of indoor tanning, but that there has been strong opposition from the tanning industry.
The authors discuss how UVR brings about tanning. This involves two types of cell, called keratinocytes, the main cell type in the outer layer of the skin and melanocytes, pigment making cells. When the skin is exposed to UVR, it causes DNA damage in keratinocytes, and this leads to the cells secreting a chemical that stimulates melanocytes to produce more pigment (melanin). The cells send each other messages, which result in the transfer of “packets” of pigment from the melanocytes to the keratinocytes near the surface of the skin, where the pigment tries to shield the nucleus of the cell from the UVR. This movement of pigment results in “tanning” of the skin. The DNA damage in the keratinocytes also causes them to produce endorphins, chemicals known to be involved in addictive behaviour, and the authors say that this may be reinforce UV -seeking behaviour.
They continue that there are few remaining doubts that UVR massively increases the risk of skin cancer. Skin cancer is the most common cancer in the US, with over a million cases in 2007. The incidence is rising faster than any other cancer, with the lifetime risk of developing melanoma in the US increasing about 2000% in the past 75 years. They state that a recent review found that those who first used a tanning bed before the age of 35 increased their risk of melanoma by 75%. The study found that those who had ever used a tanning bed increased their risk of melanoma by 15% compared to those who had never used a tanning bed (relative risk 1.15, 95% confidence interval 1.00 to 1.31). The study also found increases in the risk of squamous cell carcinoma (a non-melanoma skin cancer) with the use of tanning beds (relative risk 2.2, 95% confidence interval 1.08 to 4.70).
The authors go on to discuss the role of UVR in vitamin D production. They state that, unfortunately, the wavelength of UVR that produces sunburn, suntan, and DNA damage, is very similar to the wavelength that leads to the production of vitamin D. They say that only a relatively short exposure to UVR is needed to produce vitamin D and that a 20 minute tanning session provides 4.5 to 7 times more UVR than is needed to produce vitamin D. They acknowledge that vitamin D has been linked to the reduction of a range of cancers in a number of studies, and that studies have also shown that vitamin D deficiency is common, especially at high latitudes, and among the elderly. They suggest that more research is needed to investigate the potential anticancer benefits of vitamin D, particularly randomised controlled trials.
They suggest that the tanning industry has used the possible anticancer benefits of vitamin D to stir up an apparent controversy over “the need to choose the lesser of two evils: skin cancer and photoaging versus cancer of various internal organs and ⁄ or the long list of other ailments”. The authors argue that while vitamin D may have anticancer benefits, these benefits could be gained by taking oral vitamin D supplements, thus avoiding the need for exposing the skin to harmful UVR. They suggest that the group most likely to be targeted by the tanning industry, white young adults and teenagers, are also the least likely to have vitamin D deficiency but are at the greatest risk of long term photodamage. They say that “Despite the importance of adequate vitamin D levels, the amount of sunlight needed to produce sufficient vitamin D is small and does not justify the need for tanning beds.” One study that supports this theory was carried out in six people with xeroderma pigmentosum, who need to avoid sun exposure as they are UV hypersensitive. It found that despite the extreme sun avoidance in this population, they still had low normal or normal levels of vitamin D metabolites.
What interpretations did the researchers draw from these results?
The researchers suggest that as the initiating event for tanning is the same as for the development of skin cancer (DNA damage) it may be impossible to ever have “safe tanning”. They suggest that levels of vitamin D can be maintained with oral supplementation if needed. They conclude, “Whereas genetic and other factors undoubtedly contribute importantly to skin cancer risk, the role of UV is incontrovertible, and efforts to confuse the public, particularly for purposes of economic gain by the indoor tanning industry, should be vigorously combated for the public health.”
What does the NHS Knowledge Service make of this study?
This thought-provoking article puts forward arguments against the existence of “safe tanning”. As the authors state, the evidence that UVR increases the risk of skin cancer is clear, and while adequate vitamin D is important for maintaining health (and may even reduce risk of some cancers), this does not mean that tanning is healthy. Most young and healthy individuals should be able to obtain enough vitamin D from their diet (in fatty fish like salmon or sardines, or in vitamin D enriched margarines and breakfast cereals) and from sensible day-to-day indirect sunlight exposure. For those who are concerned about their vitamin D levels, a vitamin D supplement would be the best answer rather than resorting to excessive outdoor tanning or sunbeds.