Monday, March 10, 2008

Interesting Globe Story on Vitamin D

When the weather is as cold and snowy as it has been this past week it is nice to think of the warm and sunny days to come. And so I want to blog (yet again!) about the importance of the sun for human health and well being. My previous posts have noted the purported benefits and harms of sun exposure. Today's Globe and Mail has this fascinating story on vitamin D. I find the story of vitamin D and sun exposure interesting for a number of reasons.

Firstly, it reveals how complex the relationship between our environment and our well being is. Of course there are often obvious ways in which we see the impact our environment can have, like when there is a drought and this destroys a harvest. But even the brutal snow storm Ontario experienced this past weekend can have an adverse impact on our health (e.g. increasing the number of serious falls, increased car accidents, delays getting to the hospital, impact on our mood, physical activity, etc.), not to mention the costs of snow removal, delays travelling, etc. For example, this story notes that, for the city of Toronto alone, the clean-up cost of this latest storm was about $4 million and as of late last week, the city had already spent $40 million of its $67 million snow budget for the year.

A second reason why I am really interested in the story of sun exposure and vitamin D is that it reveals how provisional we should be about complex empirical matters, even those things that are taken to be established parts of the medical orthodoxy. Too much exposure to the sun, for example, can be harmful. It can increase the risk of skin cancer. But we must also be aware of the possibility that harms (e.g. increased risk of other types of cancer) can result from lack of sun exposure. And the real challenge is to find what constitutes a reasonable balance between these two potential dangers. And this is were the story of taking vitamin D is interesting. When assessing the potential harms of pursuing something we must also consider the potential harms of not doing anything. So the story of vitamin D supplements illustrates the importance of evolutionary history and the complex challenges we face in trying to pursue responsible risk management.

Here is a sample from the Globe story:

In the summer of 1974, brothers Frank and Cedric Garland had a heretical brainwave.
The young epidemiologists were watching a presentation on death rates from cancer county by county across the United States. As they sat in a lecture hall at Johns Hopkins University in Baltimore looking at the colour-coded cancer maps, they noticed a striking pattern, with the map for colon cancer the most pronounced.
Counties with high death rates were red; those with low rates were blue. Oddly, the nation was almost neatly divided in half, red in the north and blue in the south. Why, they wondered, was the risk of dying from cancer greater in bucolic Maine than in highly polluted Southern California?

...It seems almost inconceivable that geography could damn someone to a life-threatening illness - that the mere fact of living in a northern country such as Canada could be a health hazard.

...The idea behind the research is simple: Humans evolved in a sunlight-filled environment near the equator, and still have countless biological processes exquisitely calibrated to the rich vitamin D levels we would have if we were still basking under the hot sun year-round.

But by migrating to higher latitudes, where strong sunlight is not present during the fall and winter, most humans upset their vitamin D metabolism, creating susceptibilities to chronic ailments that research is now linking to insufficiencies.

...One study, in the journal Circulation, found that those with low vitamin D status had a 62-per-cent increased risk of heart failure. Another, published in Archives of Internal Medicine, found that those who take vitamin D supplements cut mortality risk by 7 per cent. A third report, by scientists at the U.S. National Cancer Institute, found that, while vitamin D didn't affect overall cancer-death risk, those with relatively high levels of it in their blood had a 72-per-cent lower risk of dying from colorectal cancer.

Other studies have found that low blood levels are an excellent predictor of who goes on to develop cancer and heart disease and that people diagnosed with cancer during the vitamin D-rich summer have a better prognosis than those diagnosed during winter.

...But even though Ms. Logan says the Canadian Cancer Society agrees that all the science on vitamin D may not be in yet, evidence to date strongly suggests that not acting on the implications of the research is risky. Cancers affected include such big killers as breast, prostate and colon, which will claim more than 10,000 Canadians this year.

"You don't need to wait for every scientific question to be answered before you take action," Ms. Logan says. "Where there is evidence of harm, even in the face of scientific uncertainty, you should do something about it."