BMJ editorial casts doubt on the notion that sunlight causes malignant melanoma

I am a big believer in the therapeutic properties of sunlight, at least some of which is related to its ability to stimulate vitamin D production in the skin. Sunlight exposure and/or heightened vitamin D levels have been associated with a range of health benefits including a reduced risk of several forms of cancer and relative protection from multiple sclerosis. I was therefore interested to read over the weekend an editorial in the British Medical Journal which highlights the importance of sunlight and vitamin D in health.

Written by Professor Michael Holick (professor of medicine, physiology and biophysics at Boston University Medical Centre in Boston, USA), the editorial details some of the evidence for the benefits of sunlight exposure and/or vitamin D including their role in bone and muscular health (vitamin D deficiency can lead to bone disease and muscular fatigue and pain). Not surprisingly, Michael Holick’s editorial mentions cancer too.

When the words ‘sunlight’ and ‘cancer’ are heard together, it’s natural for our thoughts to turn to skin cancer. There are three main forms of skin cancer: what are known as ‘squamus cell carcinoma’ and ‘basal cell carcinoma’, and ‘malignant melanoma’. The first two tend to develop on the most sun-exposed parts of the body (e.g. the top of the ear) and are generally very treatable. Malignant melanoma, on the other hand, is generally much less treatable, is quite often deadly, and is usually the major reason cited regarding why we should protect ourselves from the sun.

However, is the relationship between sunlight exposure and risk of malignant melanoma as clear-cut as we are generally led to believe it to be? Michael Holick’s editorial contains information that might cause us to question traditional wisdom on this. He writes: Notably, non-melanoma skin cancers occur on the most sun exposed areas, such as the face and hands, whereas most melanomas occur on the areas least exposed to the sun [2]. Intermittent and occupational sun exposure has been found to reduce the risk of malignant melanoma [2-5].

In short, Professor Holick appears to be asking: “If sunlight exposure causes malignant melanoma, how come it tends to develop on parts of the body that are not typically very sun-exposed, and how come there is evidence linking sun-exposure with reduced risk of this condition?” Professor Holick appears to cast considerable doubt on the notion that excessive exposure to sunlight is a major risk factor for malignant melanoma.

Even if it is, I still think it’s worth bearing in mind all the benefits that may come from sunlight that may offset any downside. For more on this, see this previous post. And for more advice on safe-tanning and natural sun-protection, see here.

References:

1. Holick M. Deficiency of sunlight and vitamin D. BMJ 2008;336:1318-1319

2. Kennedy C, et al. The influence of painful sunburns and lifetime of sun exposure on the risk of actinic keratoses, seborrheic warts, melanocytic nevi, atypical nevi and skin cancer. J Invest Dermatol 2003;120:1087-93

3. Holick MF. Vitamin D deficiency. N Engl J Med 2007;357:266-81

4. Grant WB, et al. The association of solar ultraviolet B (UVB) with reducing risk of cancer: multifactorial ecologic analysis of geographic variation in age-adjusted cancer mortality rates. Anticancer Res 2006;26:2687-99

5. Moan J, et al. Addressing the health benefits and risks, involving vitamin D or skin cancer, of increased sun exposure. Proc Natl Acad Sci 2008;105:668-73

9 Responses to BMJ editorial casts doubt on the notion that sunlight causes malignant melanoma

  1. Cybertiger 16 June 2008 at 3:39 pm #

    John Briffa says,

    “Professor Holick appears to cast considerable doubt on the notion that excessive exposure to sunlight is a major risk factor for malignant melanoma.”

    My first exposure to the melanoma was as a medical student on an elective period in Malawi. When quizzed about the case, I did not get the diagnosis right. The old man had a large black lump on the sole of his foot and he was about to be wheeled into the operating theatre to have his foot chopped off.

    PS. Perhaps calcium and vitamin D supplementation in the elderly, ostensibly to prevent osteoporotic fractures, is a better bet at preventing killer influenza than the flu shots ” and a lot less expensive.

  2. David Wayne 16 June 2008 at 6:49 pm #

    Hi Dr. Briffa – I have been a lurker here for a few months and have greatly enjoyed your blog. Today you give me the opportunity to comment for the first time with a question that has been bugging me a bit. Please forgive me if this question is completely ignorant but I was wondering what the rate of skin cancer/melanoma is in nations/peoples that aren’t as able to protect themselves from the sun as we are in the west. I am thinking particularly of African peoples who, it seems to me, must live most of their lives out in the sun. Also, with me being from America, I think back to our pioneer days and all of the cowboys and farmers and other folks who went west and had to spend most of their lives out in the sun – is there any way to know if they had high rates of skin cancer? Again, this may be an ignorant question but I was wondering if there might be another explanation for some of these things than overexposure to sun. Thanks!

  3. Sue 16 June 2008 at 11:53 pm #

    Doesn’t dark skin provide more protection from the sun?
    Also, dark skinned people have a harder time getting vitamin D from the sun?

  4. Mo 17 June 2008 at 3:48 pm #

    I think it’s a bit of a chicken and egg scenario. If you have an optimal level of vitamin D you have better UVB protection, however to get better UVB protection you first need UVB to make vitamin D…

    Humans have evolved into only seeking the sun periodically, so in this case their levels of vitamin D are usually low and so they’re likely to burn and increase cancer risk before building optimal vitamin D, if at all. On top of this sunscreens decrease D production.

    The over simplification of the sun being bad at all costs seems to be a major detriment to the public.

  5. Cybertiger 18 June 2008 at 1:20 pm #

    I love this piece about vitamin D and influenza from the ‘Vitamin D Council’ in sunny California. Meet those lovely twin ladies, Ms. Acquired Immunity and Ms. Innate Immunity,

    http://www.vitamindcouncil.org/newsletter/2006-oct.shtml

    I note that Mr John Cannell MD, psychiatrist and Executive Director of the ‘Vitamin D Council’, has recently been allowed some space in the rapid response section of the BMJ.

    http://www.bmj.com/cgi/eletters/336/7657/1371

  6. Cybertiger 18 June 2008 at 4:15 pm #

    I think it is worth highlighting the words of GP, Dr Avril Danczak, who posted a rapid response along the Holick editorial.

    “Fustratingly, suitable oral treatments have become unavailable in the last year and it can be hard to get sufficient replacement levels in many patients. There is no suitable daily supplement of Vitamin D alone listed in the BNF, and over the counter vitamins are usually mixtures, with doses of Vitamin D too low to replenish stores in the severely deficient patient.Preparations of Vitamin D for daily use contain calcium, which often causes constipation and hence poor adherence. High dose oral Ergocalciferol preparations are effective and popular with patients,but these have been not available in pharmacies locally for some time due to “manufacturing difficulties”. No one seems to be responsible for ensuring supplies of Vitamin D are adequate. Injections are painful, use more staff time and require medical input. It is also fustrating that almost all the Vitamin D preparations contain gelatine, which makes them unsuitable for those who wish to observe Halal principles.”

    http://www.bmj.com/cgi/eletters/336/7657/1318#197291

    But I especially liked her penultimate paragraph,

    “The reduction in all cause mortality seen with Vitamin D supplementation (referred to by Sievenpiper et al in their article BMJ 2008;336:1371-4) is not matched by statins. We spend millions ensuring that people get their statins, shouldnt we do the same for vitamin D? “

    Hear, hear! It’s heartening to know that for some doctors, the penny has dropped, about the very modest value of statins.

  7. MinorityReport 19 June 2008 at 12:30 pm #

    CT: “very modest value of statins”. Surely you can’t have missed out on the financial incentives to push them to all the patients who can still make it to your surgery?

    http://www.dailymail.co.uk/health/article-554590/Four-million-Britons-need-statins-says-health-tsar.html

    “Prof Boyle admitted to the BBC that clinical studies have shown 99 per cent of this group will gain no benefit from taking the drug.”

  8. Paul Anderson 22 June 2008 at 11:25 am #

    It is important to note that most GP’s are part owners of their practice, and that many are heavily influenced by the profit motive. My own experience is that many doctors are more concerned by the health of their profit and loss account than they are about the health of their patients. In fact my doctor pretty much said as much to me last week.

    One of the telling comments in the radio 4 programme on statins was that the doctor interviewed was happy to prescribe statins for his patients (in order to meet targets and presumably receive financial benefits) but wound not take them himself – presumably because the side effects outweighed the negligable benefits – if in fact there are any (where all cause mortality is concerend).

    In my view an opportunity was missed when the NHS was set up. Doctors should have been employed directly by the NHS rather than operating, by and large, as a series of small partnership businesses.

    In my expereionce the value of drugs has been greatly overplayed. Perhaps this is inevitable when patients are allocated 10 min slots. It often seems to me that doctors test for the sake of testing but seem ill equiped to interpret the results of the tests they order. The choelsterol tests and thyroid tests are cases in point – falling within the normal range doesn’t necessarily mean good health. Current tests and interpretations of the results are inadequate, and have little bearing on the patients health.

    Mention vitamin D levels and the doctor seems either bemused or disinterested. Suggest you would consider taking a statin and you have his undivided attention. I wonder why?

    Paul Anderson

  9. Cybertiger 22 June 2008 at 8:38 pm #

    Paul Anderson said,

    “My own experience is that many doctors are more concerned by the health of their profit and loss account than they are about the health of their patients.”

    I’m a GP (a salaried one) and I just know this is true, so true. GPs will always jump through the hoops needed to maximise profits. And statins really are a scam, an awful scam.

    Read this in the BMJ from Malcolm Kendrick, another salaried GP. It made me weep.

    http://www.bmj.com/cgi/content/full/334/7601/983

    Think about the money (and lives) that could have been saved if we had abandoned the absurd wars on Iraq, cholesterol and Afghanistan.

Leave a Reply to David Wayne Click here to cancel reply.