Vitamin D and the Big C

There’s a joke that goes “what’s the difference between a conspiracy theorist and an investigative reporter?” – Answer: “The first thinks someone is out to get him, the second can prove it.”

Okay, so it’s not a great joke. What can you expect from someone who thinks medicine, politics and economics is fun?

There are few good investigative journalists in New Zealand. I think that Ian Wishart is one. Regardless of what you think of his politics (and I, by no means, always agree with him), he nearly always produces a reasoned, well-research argument. However, in this weeks TGIF, he rather overdoes what could have been a good article on Vitamin D.

As Ian points out lack of Vitamin D has been implicated in the development of a number of cancers, including colon, lung and breast cancer. There have been a number of studies indicating that Vitamin D supplementation may help in the prevention of these cancers. Vitamin D is also made in the skin on UV light exposure, so you can augment your Vitamin D levels by both eating more Vitamin D rich foods (Mostly fish and dairy) and by increasing sun exposure. So far so good.

Unfortunately Ian goes on to castigate the Sunsmart “slip, slap, slop” message thus:

“Expressed another way – and this is the horror story the health officials don’t know how to break to the public – the publicity campaign to reduce New Zealand’s 300-a-year skin cancer mortality rate is quite possibly a factor in the deaths of 4,000 other New Zealanders each year. That would make the sunsmart message one of the worst own-goals in the history of medical science. ”

The figure of 4000 deaths seems to come from the same dark fantasy world as Helen Clark’s 60 body bags. You cannot take a figure like deaths from colon cancer and say “well, a 50% increase in survival means that x number of people who died should have survived.” For one thing, you have no idea how many of these people had inadequate Vitamin D levels. Nor do you know if Vitamin D supplementation or sun exposure would actually prevent these deaths. All you know is that there is a correlation. And none of the current studies is a single or double blind prospective trial (e.g. give Vitamin D and see if it works). The trials are all longitudinal (i.e. takes all the colon cancer cases and sees what the Vitamin D level is in the ones that died). 

Ian also hauls the Breast Cancer Foundation over the coals for not promoting sun exposure, but lobbying for Herceptin. Vitamin D has been shown in a small prospective study to reduce death from breast cancer by 75%. This was a single, poorly designed study, Ian is pitting against more than a dozen large, well-designed clinical trials. Me, I would continue to lobby for Herceptin and suggest that swallowing some Vitamin D may not be a bad thing.

The silly thing about the whole Vitamin D debate is that Vitamin D is manufactured incredibly fast in the skin, on exposure to UV radiation. It takes only a few minutes to manufacture enough Vitamin D for a week. Sunscreen does not fully block UV rays (even factor 60 barrier cream does not) so it just take a bit longer to manufacture. Most of us only put on sunscreen if we are planning on spending hours in the sun, rather than a few minutes. It is nuts to reduce the effectiveness of the Sunsmart message by suggesting a little sun may be good for you. Almost everyone is going to get sufficient sun exposure anyway and it is very difficult to give a blanket recommendation, as people differ markedly in their sun tolerance. 

Dr. Gilcrest of the Department of Dermatology, Boston University School of Medicine, suggests that 

“Those population groups most likely to be vitamin D deficient (and presumably insufficient, if that term is accepted) are indeed unlikely to use sunscreens at all; these groups include inner city dark-skinned minorities, frail elderly who are often home-bound or institutionalized, and Middle Eastern women who wear the bourka, and therefore expose very little skin to the sun.”

The entire article is well worth reading and not overly technical.

In fairness to Ian, his final advice I have no problem at all with, so I’ll quote it to finish:

“In the meantime, the message is still simple: try and get five minutes of topless sunbathing a day, or ten to 15 minutes if just arms and face are exposed – but avoid getting sunburnt and ensure you use sunscreens and appropriate clothing to protect through the hottest time of the day. ”

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