When judging the effects of any factor on health, there is a tendency by scientists and the medical profession to focus on it’s effect on defined conditions. For example, we hear a lot about the supposed ability of a raised blood cholesterol to increase the risk of heart disease or the link between cigarette smoking and lung cancer. However, one could argue that if we really want to be able to give individuals the best information and advice we can about the effect that any factor may have on health then we might look at the broadest measures of outcome available, such as overall risk of death (also known as total mortality). The reason for this is that some factors can have both negative and positive consequences. And a classic example of this is sunlight exposure, which although is linked with an increased risk of skin cancer, is also associated with a reduced risk of a variety of other cancers. For more on this, see here.
Dermatologists, perhaps not surprisingly, tend to advise us against excessive exposure to sunlight. However, the risk here is that in so doing individuals may end up putting themselves at increased risk of several common forms of cancer and maybe overall risk of death too. Also, while many of us wouldn’t know it, while we often hear that sunlight is a potent cause of malignant melanoma (an often deadly form of skin cancer), the reality is the association between sunlight exposure and this specific form of skin cancer is far from assured. I wrote about this recently here.
With all this in mind, I was very pleased to see a couple of pieces in the British Medical Journal recently in which a British dermatologist Sam Shuster and Australian professor Scott Menzies debate the role that sunlight exposure has on risk of malignant melanoma. Scott Menzies has a conventional view on this, but Sam Shuster in his piece argues quite strongly, I think, that sunlight exposure is not an important factor in the development of malignant melanoma. He also refers to other potential benefits from sunlight that we need to be aware of when giving advice about sun exposure. You can read his thoughts here, as well as Professor Menzies’ here.
In today’s British Medical Journal I was interested to read some of the responses to the debate. Some, again not surprisingly, did not share Sam Shuster’s take on this subject. One of the letters published today [1] comes from a dermatologist, Ashley Cooper, who castigates Shuster and tells us that: The references quoted in his article are not a fair representation of the body of scientific evidence available to us, and when mixed with selectivity and conjecture, they cannot be relied on to form concrete opinion. Yet, he offers no references of his own to support this stance. He concludes by writing: We spend a lot of our time trying to convince habitual sun worshippers to cover up when we remove their multiple basal cell and squamous cell carcinomas. If we are now to tell them that ultraviolet light may protect against some forms of cancer including melanoma, I will go and get my hat.
This letter is followed by a response [2] from the authors of a recent paper in the British Medical Journal which highlighted the issue of vitamin D deficiency [3]. An editorial that accompanied this was the focus of my blog post (referred to above) here. The authors of this response draw Dr Cooper’s attention to their previous paper and accompanying editorial, and state: The evidence linking major cancers”including breast, prostate, pancreas, and colon”to UVB light under-exposure is actually rather stronger than is the evidence linking melanoma (quantitatively responsible for an order of magnitude fewer deaths) to UVB over-exposure.
This debate highlights how the more we as specialty doctors diverge from the common stem of general internal medicine that nurtured us, the greater the risk of our missing the bigger picture when an issue transcends specialty boundaries. How refreshing, I think it is to see some doctors who are prepared to take a such a wide view of the impact of sunlight on health, rather than the usual skin-focused one we get from most (though not all) dermatologists.
The authors of this letter raise another important point which alludes to the need for doctors to give their patients the very best advice we can, and how a failure to do so may result in a lack of trust in the medical profession. Specifically, they state: Doctors need to be open and honest with their patients and, if called on to do so, the general public. Where our opinion is founded largely on our own personal experience (however extensive), but where the hard evidence is incomplete or indirect, this needs to be made clear to our interlocutors, else we may in future years forfeit the professional trust bestowed on us.
References:
1. Cooper AJ. Consequences of saying sun is not major cause of melanoma. BMJ 2008;337:a1126
2. Quinton R, et al. Time to go to get your hat. BMJ 2008;337:a1130
3. Sievenpiper JL, et al. Severe unrecognised severe vitamin D deficiency. BMJ 2008;336:1371-4
