As an extension of the study we also measured concentrations of 1,25-hydroxy vitamin D. This fraction of vitamin D is believed to be regulated by 25-hydroxy vitamin D concentrations via a negative feedback mechanism. We found a rise in 1,25-hydroxy vitamin D concentrations over the summer in people using sunscreen, but the rise was smaller than that among those using placebo. In a small group there was a lower, but not significantly different, concentration of 1,25-hydroxy vitamin D at the end of summer. However, this occurred in the presence of a substantial rise in 25-hydroxy vitamin D concentrations (the vitamin D fraction that controls 1,25-hydroxy vitamin D) in all subjects. We also made it clear in our paper that the 1,25-hydroxy vitamin D concentrations of all the participants in the placebo and sunscreen groups remained within the normal range all the way through the study.

The article opens with the statement that certain professionals embrace the notion that “sunlight is bad for health,” implying that the message has been to avoid sun exposure. This misrepresents the advice given, which includes “avoiding excessive sun exposure” and “encouraging gradual sun exposure.”^1-2

No short article can do justice to the extensive research, both epidemiological and experimental, into the role of exposure to ultraviolet radiation in the aetiology of skin cancer. The limitations and uncertainties about our understanding of the problem have been the subject of international, interdisciplinary debate. The dilemma facing those who wish to prevent extensive morbidity from skin cancer, and rising mortality from melanoma, is that effective primary prevention may take 20 years or more to reduce the incidence of disease. As is the case with the prevention of other diseases, there has been much pressure to promote lifestyle and dietary changes.

Ness et al suggest that early detection and treatment may be more beneficial than primary prevention in reducing mortality from melanoma, but in countries with a low incidence of melanoma we have yet to agree on a cost effective strategy for early detection.^1-3,1-4 Nor do the authors address the psychological and financial costs of diagnosis and treatment.

Primary prevention undoubtedly brings costs as well as benefits. However, there is insufficient evidence at this stage for Ness et al to suggest that recommendations on sun exposure should be promoted to prevent one disease at the expense of another. It may well be that greater understanding of the problem will enable development of recommendations on sun exposure that can benefit more than one condition.

Now that we live much longer, however, exposure to ultraviolet radiation has become of major importance. It causes photoageing of skin in virtually everyone, particularly the fair skinned, inducing a dry, often itchy, wrinkled, blotchy, telangiectatic effect,^2-2 and skin cancer in a significant but steadily increasing minority. About 50000 people in the United Kingdom develop skin cancer each year, nearly 2000 of whom die; however, the number of cases is beginning to fall in countries, such as Australia, where community ultraviolet avoidance programmes are well established.^2-3 The authors assert that these death rates are not very high and that only a small reduction will be achieved by avoiding sunlight. Nevertheless, any skin cancer is detrimental to the sufferer and costly to health services, particularly when preventive measures are readily available. The high outlay on cosmetics and surgery to repair photoageing could also be significantly reduced.

Ness et al further state that mental health, and particularly seasonal affective disorder, is improved by sunlight. But this effect is by exposure to the essentially harmless visible light spectrum through the eye, not to damaging ultraviolet radiation through the skin.^2-4 Similarly, vitamin D is readily available in a normal diet, and not sunbathing is unlikely to lead to a deficiency.^2-5

The question posed is certainly reasonable. However, the article is flawed by superficial interpretation, a disturbing tendency to equate conjecture with evidence, and a failure to appreciate the adverse effects of sun exposure experienced by people living in other parts of the world. For example, the authors claim that reductions in mortality from melanoma by reducing exposure to the sun will be small and suggest that it would be better to train the public to consult doctors at an earlier stage in the disease process. Even in countries with low rates of melanoma, such as England and Wales, these claims are contentious; when applied to the sun ravaged populations of Australia, New Zealand, and low latitude United States, they are incomprehensible.

Two possible benefits of sunlight exposure were expounded: a reduction in coronary heart disease and improvements in mood and wellbeing, although the evidence proffered for these claims was extremely weak. Assuming that high levels of sunlight exposure are beneficial, then at the crudest level fair skinned Australians might be predicted to have lower cardiovascular mortality and fewer suicides than their northern European cousins. However, death rates for heart disease among Australian men in the MONICA cohorts are higher than those for Iceland, Denmark, or Sweden,^3-2 and suicide rates in Australia are among the highest in the world.^3-3 Moreover, people who migrate from England, Wales, and Ireland to Australia commit suicide at higher rates than those who remain behind.^3-4

Several studies have examined the relation between sunlight exposure and internal malignancy. Several of these give sufficient information to allow the effect of changing sunlight exposure on the expected rate of malignancy to be estimated. All the studies show a negative relation of similar magnitude (table), particularly for breast and colon cancer.

In 1995 there were about 30000 new cases each of breast and large bowel cancer in the United Kingdom and about 30000 deaths from the two tumours combined. The most conservative of the estimates from the above studies suggest that a 10% decrease in sunlight exposure might lead to a 6% increase in these figures. This would approximate to 1800 extra cases of each of the tumours and 1800 extra cancer deaths. This figure exceeds the total number of deaths due to malignant melanoma, which are unlikely to be totally prevented by such a modest reduction in sunlight exposure.

Turning to the substantive points raised, Marks and Melia suggest that we have misrepresented the results of a randomised controlled trial of sunscreens.^5-3 In this study 113 adults living in Victoria, Australia, were randomised to either sunscreen or placebo over the course of an Australian summer. Concentrations of 25-hydroxy vitamin D and 1,25-hydroxy vitamin D were measured at the beginning and end of the study. The rise in 25-hydroxy vitamin D concentrations was similar in both groups, but the rise in 1,25-hydroxy vitamin D was lower in those allocated to receive sunscreen: a 1.5% increase from baseline versus a 13.3% increase (P=0.009). To call this “a slightly smaller change,” as Marks does, is surely misleading. This study population was exposed to much stronger sunlight than that in temperate climates; furthermore, the sample studied probably experienced a higher than average sun exposure for Australians as they had a history of solar keratoses. Despite these characteristics the study provides evidence that sunscreens may affect vitamin D values. An extreme example of the danger of extrapolating from the Australian experience to less sunny climates is provided by the recent report of a case of rickets in a white child in Toronto who had been covered in sunscreen.^5-4