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C O N T R O V E R S I E S I N DE R M A T O L O G Y DOI 10.1111/j.1365-2133.2006.07261.x A new government policy is needed for sunlight and vitamin D O. Gillie Health Research Forum, 68 Whitehall Park, London N19 3TN, U.K. Correspondence O. Gillie. E-mail: [email protected] Accepted for publication 15 December 2005 Conflicts of interest None declared. The British Isles are often thought to have a mild climate—winters with little snow and temperatures generally above freezing, while summers are seldom if ever uncomfortably hot. But in one respect the British climate is extreme: we get very little bright sunshine. The British Isles are located so far north that for 6 months of the year the sun is not strong enough to enable vitamin D synthesis in exposed skin. In summer the sky is often cloudy or overcast and, even when the sun is strong and bright, the air temperature may be too cold for clothes to be removed comfortably. This lack of sunlight leads to a low vitamin D level in the British and Irish population and this is now being recognized as a major cause of ill health. And government advice to stay out of the sun in the middle of the day, which is the best time for vitamin D synthesis in the skin, adds to the problem. In this article I consider the problem of vitamin D insufficiency from the earliest days of human settlement in these islands up to the present day. I outline recent findings about the consequences of vitamin D insufficiency for health. And I suggest that optimum health is more likely to be achieved by safe sunbathing without burning than by the SunSmart advice presently advocated by government and Cancer Research UK (CR-UK). Europe some 20 000 years ago following the ice age.1 The climate of northern Europe provided a new evolutionary challenge to humankind. In tropical Africa there is generally plenty of sunlight every day of the year whereas in northern Europe we have a vitamin D winter when synthesis of the vitamin is impossible. White skin synthesizes vitamin D six times faster than dark skin,2 enabling efficient use to be made of short sunny periods on cloudy days. A white skin also enables better use to be made of the thin sunlight that we get at the beginning and end of the summer season, thus extending the period when vitamin D can be synthesized for growth and reproduction. This must have given white skin a strong selective advantage during the colonization of northern Europe.3 Low levels of vitamin D are a cause of infertility4 and seem to be associated with an increased risk of tuberculosis.5,6 These two factors together were probably responsible for a strong selection pressure that fixed skin colour genes favouring greater production of vitamin D, so enabling more successful reproduction and enhanced survival of the species. Women and children have lighter skins than adult men.7 It has been suggested that this enables them to make best use of small amounts of sunlight for good reproduction and growth while men, who traditionally spent more time foraging in the open, had darker skins that protected them from sun damage. Evolution of white skin Humans evolved in tropical Africa—we now know that for sure. Modern human beings (Homo sapiens) first colonized northern Oliver Gillie BSc PhD is former medical correspondent of the Sunday Times and former medical editor of the Independent. He is the author of Sunlight Robbery: Health Benefits of Sunlight are Denied by Current Public Health Policy in the U.K. published by Health Research Forum (http://www.healthresearchforum.org.uk). 1052 Industrial lifestyle brings low levels of vitamin D Our lifestyle has changed drastically in the last 200 years and in the last 40 years it has changed with an accelerating pace. Few people are now employed in agriculture or outside jobs. We spend more time in cars, offices and houses, getting less sun than ever, while air pollution in cities reduces the amount of ultraviolet (UV) radiation that reaches ground level. 2006 British Association of Dermatologists • British Journal of Dermatology 2006 154, pp1052–1061 A new government policy is needed for sunlight and vitamin D, O. Gillie 1053 These problems of city life were recognized as the cause of rickets early in the last century and in the 1930s, following the discovery of vitamin D, margarine began to be fortified with vitamin D. This largely prevented rickets, but in the last 30 years the disease has reappeared, mostly in the immigrant population whose vitamin D levels are much lower as a result of their skin colour.8 However, rickets is only the most florid manifestation of vitamin D deficiency or insufficiency. Today 12% of adults of working age in the U.K. are deficient in vitamin D and about 60% obtain insufficient vitamin D (B. Boucher, personal communication, 2005: summary of data on prevalence of vitamin D deficiency and insufficiency in the U.K. taken from the National Diet and Nutrition Survey data).9 In fact almost everybody in the U.K. obtains suboptimal amounts of the vitamin. Over the last 10 years it has been realized increasingly by a small number of scientists and doctors that vitamin D is associated with many chronic diseases and is probably a significant cause of many of them—see Table 1 for details and references. Chronic disease associated with inadequate vitamin D levels Evidence linking chronic disease with insufficient vitamin D, or low exposure to sunlight, comes from several different scientific approaches which give similar answers. Studies of variation in chronic disease with latitude, altitude, season, skin colour, holiday or lifetime exposure to the sun, and also case– control studies all show an association between lower sun exposure and disease. While individual observations may be explained in various ways there is only one conclusion that is consistent with all these observations: a low gain in vitamin D, resulting either from low exposure to sunlight or inadequate diet, is an important risk factor for a number of chronic diseases (see Table 1). In fact it is beginning to seem likely that a low gain in vitamin D will prove to be a major lifestyle risk factor as significant in causation of disease as smoking, obesity or alcohol. While vitamin D has long been known to be the cause of the classic bone diseases—rickets, osteoporosis and osteomalacia—few doctors have been aware until very recently of the link with cancer and other chronic diseases including multiple sclerosis, hypertension, diabetes, arthritis, autoimmune disease and a multitude of other ills.10,11 The list is so long that, regardless of evidence, it has aroused scepticism. But it is now known that vitamin D is not simply processed in the kidney to make the active hormone that controls calcium in bone. Some 30 or more tissues and organs have receptors for vitamin D.12 The vitamin is captured in these tissues and processed into its hormone form which acts in a paracrine fashion, both directly on local cell metabolism and also on the genes, switching them on or off.13 Vitamin D actively controls certain genes involved in cell differentiation and can switch on genes that programme cell death (apoptosis). These are processes that play a crucial role in preventing initiation of clones of cells that may become malignant.14 Women in the U.K. (latitude 50–60) have a higher risk of developing breast cancer than women in the relatively sunny northern states of the U.S.A. (latitude 40–50), who in turn have a higher risk of breast cancer than women living in subtropical Florida (latitude 25–30).15,16 Take a look at the ‘Cancer Maps’ on the National Cancer Institute website [http://www3.cancer.gov/atlasplus/index.html (accessed 18 January 2006)]. As you head north from Florida towards Canada the death rates for prostate, breast and colon17 cancers steadily increase. This correlation has been found for more than 16 different cancers and cannot be explained by differences in diet, social class or race.15 These same cancers also tend to be more common in northern countries of Europe than they are in either the United States or in the southern countries of Europe. Such geographical variation, attributable to differences in sun exposure, has Table 1 List of diseases thought to be caused, at least in part, by low vitamin D levels. Low levels of vitamin D or insufficient sunshine may cause or increase the risk of the diseases listed below, according to epidemiological and other evidence.10,11 The strength of the evidence varies substantially for different diseases but satisfies many of the well-known criteria for causation considered by Sir Austin Bradford Hill.69 Cancer28,29,70 Nervous system diseases39,40,71–74 Circulatory and metabolic disease75,76 Reproductive disease4,77–83 Immune system disease (autoimmune disease)11,56,84 Bone disease8,48,58,85–88 Pain89 Infections5,90 Breast, ovary, prostate, bowel (and intestinal polyps), pancreas, lymphoma, multiple myeloma and thyroid cancers; possibly a risk factor in some 16 or more different cancers Multiple sclerosis, schizophrenia and possibly other nervous system disease Heart and blood vessel disease including heart failure and heart attack, hypertension, metabolic syndrome (syndrome X) and diabetes type 2 Polycystic ovary syndrome, premenstrual syndrome including migraines, preeclampsia, some infertility Diabetes (type 1), rheumatoid arthritis, psoriasis; possibly plays a part in a number of other autoimmune diseases Rickets, osteoporosis, osteomalacia, osteoarthritis; may also be a risk factor for tooth decay and tooth loss Rheumatism, low back pain and other persistent nonspecific musculoskeletal pain is associated with low vitamin D and/or unrecognized osteomalacia Pneumonia and tuberculosis 2006 British Association of Dermatologists • British Journal of Dermatology 2006 154, pp1052–1061 1054 A new government policy is needed for sunlight and vitamin D, O. Gillie not generally been taken into account by those who have studied geographical differences in diet. The Mediterranean diet is reputed to protect against cancer and heart disease. But at least part of what was thought to be the benefit of this diet may actually come directly from the powerful Mediterranean sun. Taken alone, geographical or ‘ecological’ evidence can be misleading. However, the geographical evidence from the United States and Europe showing a link between digestive system cancers and latitude is backed up by a similar study from Japan.18 To get the same result in countries with such different diets and cultures suggests that an unknown confounding factor is unlikely to be the cause. There is also substantial evidence supporting the association between cancer and vitamin D using entirely different methodology: i.e. careful case–control studies.17,19–24 For example, British men who have regular sunshine holidays or who sunbathe regularly are less likely to suffer from prostate cancer than others who holiday at home or stay indoors. And if the men who take foreign holidays and sunbathe do develop prostate cancer they do so at an older age than men who have few foreign holidays and sunbathe less.25 This research, undertaken by Professor Richard Strange and others at the University of Keele, is what academics like to describe as ‘robust’. Professor Strange was surprised to get such a clear-cut result and worried that it might have been a chance finding. So he repeated the survey and obtained exactly the same result. There seems to be little doubt that investment in sunshine holidays and careful sunbathing may stand a man in good stead in preventing prostate cancer later in life. Other evidence suggests that similar benefits from sunlight exist for women. In Norway, women whose breast cancer is diagnosed in the summer live longer than women whose breast cancer is diagnosed in the winter, according to Professor Johan Moan of the University of Oslo.26 Prostate, colon, lymph gland and lung cancer behave in a similar way in Norway—summer-diagnosed illness does better than winterdiagnosed illness. Furthermore, the result for lung cancer has been repeated by researchers at the Harvard School of Public Health.27 People with nonsmall cell lung cancer, the commonest kind, are more than twice as likely to survive 5 years following diagnosis if their disease is first found in summer. Higher consumption of foods containing vitamin D were also found to improve survival of these lung cancer patients. It appears that a higher level of vitamin D at the time of diagnosis aids treatment, possibly by facilitating apoptosis. Edward Giovannucci, professor of public health at Harvard and senior author of the lung cancer study, says in a wideranging review of vitamin D and cancer: ‘In vitro, animal and clinical studies strongly indicate that vitamin D may have anticancer benefits, including against progression (such as metastasis) against a wide spectrum of cancers. Thus, vitamin D could be potentially beneficial against either incidence or mortality, or both.’28 William Grant, an independent researcher, has calculated that some 22 000 cancer deaths in the U.K. may be attributed to insufficient sun exposure or too little vitamin D.29 Put crudely, if we obtained as much sun in the U.K. as they do in Florida we would have some 22 000 fewer cancer deaths per year. But we do not need to go to live in Florida. People living in the U.K. could obtain greater exposure to the sun, and could reasonably expect to reduce their risk of cancer, if they were encouraged to sunbathe by a positive public health policy towards sunlight. However, CR-UK remains sceptical of the link between cancer and insufficient vitamin D. Carolan Davidge, spokesman for the charity, has insisted: ‘There is certainly no clear evidence that increasing the sun exposure of the general U.K. population will reduce the incidence of common cancers. Indeed it is irresponsible to suggest that prevention of these cancers is a simple matter that could be achieved by sunbathing.’ Skin cancer There is of course a risk of skin cancer for those who bake or burn themselves in the sun. Those who expose pale untanned skin to too much sun too quickly may have an increased risk of skin cancer. But it has been known for a long time that people who work outdoors and get regular exposure to the sun are less likely to get melanoma, which is responsible for the large majority of deaths from skin cancer.30 Recently one study has found that people who have longer lifetime exposure to the sun without burning are less likely to get melanoma than those with less exposure.31 And most surprising of all, another study has found that people with melanoma live longer if they have previously had greater exposure to the sun.32 So careful sunbathing, with measured exposure to the sun, may actually reduce rather than increase the risk of melanoma, reduce the overall risk of death from skin cancer, and improve survival for those who do develop melanoma. This is consistent with evidence summarized above, which suggests that vitamin D or sun exposure protects against many types of cancer and also increases survival of people who have developed the disease.28 It has often been asserted that two-thirds of melanomas are caused by exposure to the sun. However, this figure has been challenged and other methods of analysis suggest that sun exposure may account for as little as 10% of the risk.33 Indeed, C.B. Begg from the Department of Epidemiology and Biostatistics, Memorial Sloan-Kettering Cancer Center, New York, concluded in 2001 that the bulk of the variation in risk of melanoma cannot be explained by known risk factors including sunlight. There are a few tantalizing clues suggesting other causes of melanoma. For example, it has been found in a number of countries that melanoma, like breast cancer, is more common in higher social classes.34 And melanoma, like breast cancer, has been found in some studies to be associated with greater height.35–37 This suggests that some of the ideas being considered as causes of breast cancer, such as increased levels of 2006 British Association of Dermatologists • British Journal of Dermatology 2006 154, pp1052–1061 A new government policy is needed for sunlight and vitamin D, O. Gillie 1055 insulin or insulin-like growth factors in the blood, could profitably be considered in connection with melanoma and indeed in vitro evidence suggests that such hypotheses are biologically plausible.38 Multiple sclerosis—a disease of dark winter days Multiple sclerosis (MS) has long puzzled doctors and scientists seeking to understand how it may be caused. At last epidemiology has come up with an explanation. It has been proven, so far as it is possible with epidemiology, that low exposure to sunlight is a major cause, and possibly the major cause, of MS. In the northern hemisphere, MS is more common in the most northern countries with longest winters: it is more common in Canada than in the United States and more common in Scotland than it is in England.39,40 In Australia MS is some five times more common in Tasmania in the relatively cold south of the country than it is in Queensland in the subtropical or tropical north.41 Increased exposure to the sun seems to protect against MS. People who get nonmelanoma skin cancer, an indication of extended sun exposure, have half the risk of developing MS compared with healthy controls.42 And observations of MS lesions in the brain have shown that the lesions increase in winter when MS symptoms are known to become worse and vitamin D levels in the blood are lowest.43 But most challenging of all to those concerned with public health: children born in late winter or early spring have a greater risk of developing MS later in life than children born at other times. This may be explained by low vitamin D levels in the mother’s body at the end of pregnancy increasing the risk of developing MS.40 Professor George Ebers, the Oxford neurologist who has been in the forefront of this research, says: ‘We have done all we can by way of epidemiological studies to pinpoint the cause of MS. There can be no doubt about the strong link with low levels of exposure to sunlight. Insufficient vitamin D could be the cause but we have not proved that yet. We now need to undertake trials.’ A policy based on misunderstanding Fear of skin cancer has led to a policy of recommending reduction in exposure to the sun with consequent reduction of vitamin D levels for those who follow such advice. CR-UK insists that casual exposure of the hands and face for about 10–15 min two or three times a week will provide people in the U.K. with sufficient vitamin D.44 But this advice is based on outdated information and a contradiction. CR-UK’s recommendation of 10–15 min casual exposure to the sun is actually calculated on the basis of an exposure at noon when the sun is strongest. However, their SunSmart programme recommends use of sun cream and avoidance of the sun for 2 h each side of solar noon—that is between 11 AM and 3 PM British Summer Time. If the SunSmart advice is followed, casual exposure to the sun will occur only before or after the 4-h period around midday, in which case very little, if any, vitamin D will be obtained. And 10–15 min will certainly not provide sufficient vitamin D. There is another problem with the scientific reasoning behind CR-UK’s advice. CR-UK’s calculation assumes that a person needs only 200 IU of vitamin D per day, a figure that is out of date (E. Yong, Cancer Research UK, personal communication, 2005; see: http://www.healthresearchforum.org.uk, accessed 23 January 2006). This figure, which recurs in the literature on vitamin D, seems to originate from the amount of vitamin D in a teaspoon of cod liver oil. A hundred years ago a teaspoon per day of the dreaded but potent substance was found to be sufficient to cure rickets, and ever since the teaspoon has been taken as a basis for calculating the daily requirement of vitamin D. However, such simple reckoning has now been superseded by the pharmacokinetic studies of Heaney and others which show that 3000–5000 IU vitamin D per day are needed for optimum health.45 If Heaney’s scientific investigation of vitamin D requirement is accepted, as it is by experts in vitamin D, then CR-UK’s calculation is out by a factor of more than ten. The policy of Government and CR-UK on sunlight is also based on an assertion, made in a report published by the National Radiological Protection Board (NRPB) in 2002,46 that casual exposure of hands and face to the sun will provide sufficient vitamin D (E. Yong, Cancer Research UK, personal communication, 2005). However, the reference provided by NRPB to support this claim fails to provide any cogent evidence.10 The reference describes observations of nine elderly patients who lived on a hospital ward near Nottingham where they had access to a sunny terrace.47 At the end of summer, three of the old people in this study had blood levels of vitamin D of < 22Æ5 nmol L)1 and so would be expected to suffer severe D-deficiency during the following winter. All the others except one had levels of D < 40 nmol L)1, which could not be expected to remain above danger levels during the following winter. Only one of the nine elderly people maintained a reasonably healthy summer level of D at 79Æ4 nmol L)1 and he had spent many hours in his garden after discharge from hospital. In fact, contrary to NRPB’s assertion, this data illustrates that an optimal level of vitamin D cannot be maintained by most people in the U.K. simply by casual exposure of hands and face. Sources of vitamin D An adult in the U.K. obtains an average of about 150 IU vitamin D per day from food (B. Boucher, personal communication, 2005). About half of the vitamin D in the average U.K. diet comes in margarine and fortified breakfast cereals (B. Boucher, personal communication, 2005), but many people do not eat these foods. Furthermore Kellogg’s, the cereal manufacturers, has recently stopped fortifying many of its products with vitamin D because of regulations in other European countries and the need for efficient production. 2006 British Association of Dermatologists • British Journal of Dermatology 2006 154, pp1052–1061 1056 A new government policy is needed for sunlight and vitamin D, O. Gillie Oily fish, the food richest in vitamin D, is eaten by relatively few people in the U.K. Even Norwegians or Icelanders, who eat much more fish than we do, cannot get enough vitamin D just from their diet. Only Inuit (Eskimos), who eat oily fish or other marine produce at virtually every meal, and Lapps, who get their vitamin D from reindeer meat, get most of their vitamin D from the diet. Vitamin supplements available over the counter in the U.K., typically providing about 200 IU per day, may double the amount of vitamin D obtained by mouth. This is enough to prevent gross bone disease, such as rickets or osteomalacia, but is not enough to prevent osteoporosis or the many other ills linked to low vitamin D.48 Much more vitamin D is needed for optimum health. So sunlight remains the major source of vitamin D for people in the U.K. who achieve anything near healthy blood levels of the vitamin. The vitamin D budget for people living in the British Isles needs to be calculated on an annual basis because in winter no vitamin D can be gained from the sun. Between 3000 and 5000 IU of vitamin D a day are required for optimum health,45 but 1000 IU per day may be taken to be the minimum desirable gain in vitamin D according to international experts. So, reckoned annually, the minimum desirable gain is 365 000 IU. Vitamin D has a half life of 6–8 weeks and so a large store needs to be accumulated in summer to last through the winter. In the British Isles sufficient summer levels to provide the minimum desirable level year round are likely to be reached only with the help of active sunbathing. The sun is generally strong enough in southern England to provide vitamin D for 26 weeks between the first week of April and last week of September. However, April is generally too cold for sunbathing, and throughout the summer cold winds or cloud frequently prevent sunbathing in southern England. The summer season is substantially shorter in Scotland where, in addition, the sun is less intense and there are more cold days. Casual exposure of the hands, arms and face two or three times a week, as suggested by CR-UK and Diffey49 might supply 1 MED (minimum erthythemal dose) to an adult in southern England, weather and time permitting. So over the 26 weeks of summer such casual exposure may supply up to 26 000 IU of vitamin D. If this exposure could be increased from three to seven times per week then at most 61 000 IU could be obtained over the summer while some 55 000 IU (150 IU per day) on average might be obtained annually from food. This adds up to 116 000 IU of vitamin D gained annually and leaves our subject with another 249 000 IU to find if he or she is to obtain the minimum desirable amount of vitamin D. In fact it makes no sense to try to increase the gain in vitamin D by increasing exposure of hands, arms and face. Excessive sun exposure may cause skin ageing and so it is preferable, as in radiology, to spread the dose. In this case the dose may be spread over all parts of the body by active sunbathing while protecting the face which tends to get over- exposed. It is obviously advantageous to protect the face as age is largely judged from facial appearance. Failure to recognize the advantage of spreading the UV dose over the whole body is a serious flaw in the advice given by the SunSmart programme. Active sunbathing that exposes the whole body may supply up to 10 000 IU per day50,51 in summer. To obtain something approaching the optimum annual amount of vitamin D in the U.K. (without travelling abroad) a person would have to sunbathe in a swim suit on about 100 sunny summer days. This is, for practical purposes, impossible even for a dedicated nudist. There are about 26 weeks (182 days) when the sun is potentially strong enough for sunbathing in the U.K., but in less than half of these will the sky be clear and the air warm enough for sunbathing. It may be possible to sunbathe wearing minimum clothing on 25 days over the summer, an average of once per week. If so, and 10 000 IU can be obtained each time, then the extra 249 000 IU of vitamin D that are needed to attain the minimum desirable annual level could be accumulated during the course of a summer. However, with our uncertain weather in the U.K. weeks may pass by without clear sun. So it makes sense to sunbathe whenever possible wearing as few clothes as possible if vitamin D sufficient for good health is to be obtained. Choosing a sun exposure policy The SunSmart programme, which advises against sun exposure in the middle of the day, is ill-suited to our climate. SunSmart is based on a model programme developed in Australia where the sun is a great deal stronger. The SunSmart recommendation that 10–15 min of sun on the face, arms and hands two or three times a week is sufficient for good health in the U.K. does not even provide the minimum requirement of vitamin D. People in the U.K. who are influenced by the SunSmart advice will obtain substantially less than average exposure to the sun and should expect to suffer a corresponding deficit in vitamin D unless they take a large supplement by mouth. Therefore it seems quite likely that SunSmart may be causing substantial ill health and is quite possibly causing more cancer deaths than it is preventing. It also worth remembering that sunlight is the normal and natural source of vitamin D for human beings and, unlike special foods or supplements, it is free. There should be very good reasons for issuing instructions which prevent people from utilizing a natural source of vitamin. SunSmart claims to reduce deaths from skin cancer but it may do this by only a few hundred per year. The risk of skin cancer may be reduced equally well by less extreme measures that encourage safe sun exposure (without burning) and at the same time boost vitamin D levels30–32 with substantial benefits in prevention of cancer of all kinds. I have developed guidance for sunbathers which I call the SunSafe advice (Table 2). This advice has been produced with 2006 British Association of Dermatologists • British Journal of Dermatology 2006 154, pp1052–1061 A new government policy is needed for sunlight and vitamin D, O. Gillie 1057 Table 2 The SunSafe advice 1 2 3 4 5 6 7 8 Sunbathe safely without burning—every day if you can The middle of the day is a good time for sunbathing in the U.K.a Start by sunbathing for 2–3 min each side; gradually increase from day to day Don’t use sun cream while sunbathing If feeling hot or uncomfortable expose a different area, cover up, move into the shade—or use sun cream When abroad, where the sun is generally stronger, expose your body for shorter times until you find out how much is safe Children benefit from sun exposure, but need guidance A tan is natural and is generally associated with good health a The sun is strongest in the middle of the day and so maximum synthesis of vitamin D occurs in the shortest possible time. This is important in our climate because intermittent cloud or overcast skies often decrease intensity of UV. Furthermore at the beginning and end of the summer the sun is strong enough for vitamin D synthesis only at midday. The lunch hour is often the most convenient time to sunbathe. safety, optimum health and reduction of skin cancer as primary considerations. SunSafe advises people in the U.K. to sunbathe as often as they can, while taking care to avoid burning, and so maximizes the vitamin D that they can obtain. The advice is based on up-to-date information about vitamin D requirements together with an up-to-date assessment of causes and risks of skin cancer. The advice is conservative, reflecting the positive health advice on sunlight widely advocated in the U.K. before SunSmart was introduced. SunSafe advice may reasonably be expected to reduce some of the 22 000 cancer deaths in the U.K. that can be attributed to insufficient sunlight, as well as much other chronic disease. I believe that SunSafe advice is safer than CR-UK’s SunSmart advice because it recognizes the importance of vitamin D for health. While SunSmart advice may be effective in reducing skin cancer it is unwise to advocate it without also recommending that those who follow it take a 1000 IU vitamin D supplement per day. Such advice has not been given hitherto and such supplements can be obtained only from abroad. The SunSmart advice has consistently been promoted with the slogan: ‘There is no such thing as a safe or healthy tan.’ This slogan was adopted in 1994 by the U.K. Skin Cancer Prevention Working Party,52 although no direct evidence was offered then or since that a tan is actually linked with disease of any kind. A campaign launched in the U.K. in 1989 (‘Are you dying to get a SunTan’) even went so far as to suggest a suntan was associated with death.53 In fact some evidence suggests that a deep tan, particularly in childhood and the adolescent years, is associated with protection against melanoma,30,54 and sunburn in childhood is actually associated with a reduced risk of prostate cancer and multiple sclerosis in later life.25,55 The 1989 campaign is a classic example of ‘shroud waving’, a poorly established scare story promulgated through the media with the intention of frightening the public and changing behaviour. While it is true that sun exposure causes death of skin cells and this is associated with tanning there is no reason to believe this is other than a normal process; and no evidence has been forthcoming to suggest that tanning leads directly to any harmful consequences. A tan is an inevitable consequence of sun exposure, and greater sun exposure, which leads to a deeper tan, has been shown to be linked with better health. So a good tan may be a fair index of good health. This certainly is the common belief, and it does no favours to the credibility of science or medicine to deny common belief when there is scientific evidence to support it. Insufficient vitamin D and/or sunlight during childhood appears to increase the risk of diabetes type 1,56 multiple sclerosis55,57 and poor bone development.58 Insufficient vitamin D and/or sun exposure may produce greater effects on children and young people than on adults because it is needed for active growth, and such effects cannot be expected always to be reversible by the provision of increased vitamin D later in life. Because sunlight is a major source of vitamin D it seems obvious that children should not be denied the opportunity for safe exposure to the sun in the middle of the day when the sun is strong enough to induce synthesis of the vitamin. However, the SunSmart programme has warned of a special risk to children and young people from exposure to the sun and advises extra special protection for children against the sun. In fact, evidence that there are special risks to children from sun exposure are conflicting. Much of the evidence suggests that there is no special association between melanoma and exposure to the sun in childhood.59,60 Indeed one study has found that outdoor activities in childhood are associated with a lower risk of melanoma.61 Of course, care must be taken that children do not overexpose themselves and suffer sunburn. This requires vigilance because children themselves generally do not understand the risks. There may be other risks from the application of the SunSmart advice. Some parents, influenced by this advice, dress their children in Foreign Legion style caps and special suits that envelope the whole body except for the hands and face which are covered with sun cream. Children dressed in this way are likely to be at risk of vitamin D deficiency unless they also take a large vitamin D supplement. CR-UK has yet to 2006 British Association of Dermatologists • British Journal of Dermatology 2006 154, pp1052–1061 1058 A new government policy is needed for sunlight and vitamin D, O. Gillie warn the public of the risks that may ensue from the use of such sun-suits and the adoption of its SunSmart advice without also taking a large vitamin D supplement. Reply to Brian Diffey I welcome the opportunity to reply to some of the points made by Brian Diffey in his accompanying article.62 Diffey compares the incidence of and mortality from various cancers in the U.K. with incidence and mortality in Australia and New Zealand. He uses these figures to question other observations which suggest sunlight is beneficial in the prevention of cancer. On the face of it comparing observations on the populations of Australia or New Zealand with the U.K. may seem appropriate because the ancestors of the large majority of people in these countries came from the U.K. Therefore the possibility of genetic differences may generally be ignored. But international comparisons of this kind are subject to difficulties of interpretation for a number of reasons. Most epidemiologists will agree that cancers are multifactorial in their causation. Sunlight is only one of several factors influencing cancer incidence. It cannot be assumed in comparing cancer incidence in Australia and New Zealand with the U.K. that the difference found is the consequence of the differing strength of sunlight in the three countries. To understand the difference in cancer incidence between these countries all possible causes need to be examined because one cause may mask another. The U.K., like other European countries, was affected by World War II in a way that Australia and New Zealand largely avoided. The German submarine patrols in the Atlantic had a devastating effect on food supplies to the U.K. which were then, as now, largely imported. Rationing of food was introduced in the U.K. in January 1940 and lasted long after the war. It was abolished in a series of stages and finally ended when meat rationing ceased in 1954. Frugal habits with regard to food were established by this wartime experience and continued in families for many years, at least until the 1960s and 1970s. The generations raised in those relatively frugal times are the ones who are now in the age group that is providing most of the cancer statistics. A plentiful diet in childhood and later is now recognized as a risk factor for a number of cancers, including melanoma, whereas a restricted diet in childhood, as caused by rationing, is associated with a reduced risk of cancer.63,64 These concepts are well supported by animal work. It has long been known from animal experiments that restriction of calories inhibits the development of cancer.65,66 The association between obesity and cancer has been well documented and the evidence is sufficient for obesity to have been designated ‘causal’ for cancers of the colon and breast by the International Agency for Research on Cancer. It has been suggested that overeating is the largest avoidable cause of cancer after smoking.67 But increased risk of cancer has also been associated with higher birth weight, accelerated or catch-up growth, and greater birth length or adult height—all of which are consequences of overeating or a more plentiful supply of food.63 Therefore the general dietary history of a country is relevant if cancer incidence or mortality of countries are to be compared. It cannot be safe to assume that the diets of people in Britain and Australia or New Zealand have been generally comparable over the last 65 years. Australia and New Zealand are food-producing countries, which have generally had food surpluses and food has therefore been cheap. Furthermore, they did not suffer shortages during World War II. Whereas in the U.K., extra food beyond that needed for bare survival has at times been unobtainable, while at other times it may have been relatively more expensive. Similar considerations apply to the statistics, quoted by Diffey, which show an increase in the incidence of breast, colon and prostate cancer, as well as melanoma, in the U.K. over past decades. The increasing availability of food in the U.K. over the decades following World War II may well be a major driving factor behind the increasing incidence of certain cancers, but other factors such as instruction to avoid exposure to sunlight in the middle of the day and insufficient vitamin D could also be involved. Population level data of the kind quoted by Diffey have proved to be useful in the past for the generation of hypotheses and in defining public health problems that need to be tackled.68 However, such data cannot be employed reliably to refute a hypothesis as Diffey has done, because there are too many possible interpretations and such data are too readily subject to confounding. Diffey argues that British adults spend an average of only 14 min engaging in activities outdoors and therefore will not have time to sunbathe. The 14 min is apparently a year-round average. On sunny summer days the average person may well spend two or three times as long in the open air, and many people will happily spend much longer outdoors. As little as 5–10 min exposure to the sun in the middle of the day in midsummer is long enough to obtain some useful vitamin D if some clothes are removed. Certainly, as Diffey points out, many people do not go outdoors a great deal and both adults and children generally walk outside less than they used to do. However, it is not necessary to walk in order to sunbathe. Most people actually enjoy sunbathing and so can be expected to respond to positive advice suggesting that they do so by sitting or lying in the sun. But I recognize that there is no one way of improving vitamin D status that will appeal to all and so I believe it is also important to increase fortification of food with vitamin D and bring official advice on use of vitamin D supplements up to date. Diffey’s Figure 4 shows that blood levels of vitamin D do not vary greatly with season or latitude. On the basis of this Diffey arrives again at the nihilistic conclusion that nothing much that anyone can do will make a lot of difference to their vitamin D level. However, there are two reasons for the similar levels of vitamin D in such different places as Norway and Australia. The first is that in industrial societies we all live similar lives wherever we are and whatever the season, and the 2006 British Association of Dermatologists • British Journal of Dermatology 2006 154, pp1052–1061 A new government policy is needed for sunlight and vitamin D, O. Gillie 1059 second reason is that cancer societies around the world have for the last 20 years or so advised the public to avoid the sun in the middle of the day when it is strongest. If on the other hand people are told that sunlight is a normal and natural source of vitamin D and that safe exposure to the sun in the middle of the day in the U.K. is possible and beneficial then they are likely to expose themselves more to the sun and obtain more vitamin D. People enjoy sunbathing and so it is not difficult to persuade them to do it and they can be instructed in how to do it safely. The SunSafe advice provided here is not simply theoretical, as Diffey suggests; it is well based in observational evidence which is available in the scientific literature. This contrasts with the SunSmart advice, which is in my view based on a narrow interpretation of outdated evidence. Furthermore, the SunSmart advice is not supported by any kind of document spelling out its rationale and providing a review of scientific evidence that might justify it. Finally, Diffey suggests that the SunSafe message might make cancer patients see their cancer as self-imposed and blame themselves for not getting sufficient sunlight, or that patients might move away from friends and family to a sunny country in the belief that this might extend their life. Whatever public stance is taken on such issues people who are so inclined may find ways of blaming themselves. People with melanoma, for example, may and often do blame themselves for having had too much exposure to the sun, not realizing that they might as well blame over-consumption of food or lack of exercise. It would be wrong to tell doctors to deny a link between sunlight and melanoma on the grounds that patients might blame themselves. For the same reason it would be just as wrong to deny the link between lack of sunlight, low levels of vitamin D and cancer. And if this convinces some cancer patients to take a winter sunshine holiday no harm would be done. Sunshine holidays will provide additional vitamin D which on available evidence might provide some extra months or even years of life. Doctors must be able to say what they believe to be true, albeit in the kindest possible way, if they are to maintain the confidence of their patients. Conclusion A wealth of evidence suggests that insufficient vitamin D is a cause of a wide variety of chronic diseases including several types of cancer. The majority of people in the U.K. and most other industrial countries have suboptimal levels of vitamin D. The cost of low vitamin D levels and consequent disease is probably billions of pounds per year in the U.K. A new government policy to develop increased levels of vitamin D in the population could be readily implemented and would not be unpopular. It would involve increased fortification of a wider variety of foods with vitamin D, revision of recommended supplements of vitamin D for people of all ages, and encouragement of safe sunbathing. Continuation of the government’s SunSmart policy, which is administered by Cancer Research UK, is unwise because it risks reducing vitamin D levels in the population and in so doing may be expected to increase the risk of certain cancers, multiple sclerosis and much other chronic disease. Note added in proof Since this article was completed several reviews of vitamin D and chronic disease have appeared which will be helpful to the reader. 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