THEGREENGROK    Planetary Watch

Cancer-Climate Link May Go With a POP

by Bill Chameides | April 27th, 2010
posted by Erica Rowell (Editor)

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Living in a cold region with lots of snow may make you more likely to get prostate cancer.

Like most men, I know that among the various kinds of cancer I may get, the most likely is prostate cancer — approximately one in six American men suffers from the disease. What I did not know is that the likelihood increases the further north you live. Now, a new study suggests that the interaction of weather and exposure to persistent organic pollutants or POPs may be factors in whether one protracts the disease.

Studies of where men with prostate cancer live show a clear north-south gradient. In the United States the incidence of the disease among 100,000 individuals varies from as little as 40 to more than 300, and the lower incidence rates are far more likely to be found in the southern states than in the northern states — although the relationship is far from “perfect.”

Possible Explanations for the Geographical Distribution of Prostate Cancer

What could explain this? Scientists have speculated that vitamin D may be at the root.

There’s a clear, negative correlation between the flux of ultraviolet (UV) radiation from the sun and the incidence of prostate cancer. Since vitamin D is generated in our body from exposure to the sun’s UV radiation and vitamin-D deficiency may be related to carcinogenesis (see here and here), it’s possible that living in a northerly clime with low amounts of solar UV may lead to low levels of vitamin D and, therefore, more susceptibility to getting prostate cancer.

If true, it kind of puts us men in a bind. Dermatologists tell us to avoid solar UV at all costs to reduce our chances at developing skin cancer, but such avoidance could set us up for prostate cancer.

Now a new paper in the International Journal of Health Geographics by Sophie St-Hilaire from Idaho State University and colleagues adds a twist.

By examining how different regional meteorological factors like cold temperatures and snowfall might contribute to the north-south occurrence of prostate cancer, they’ve taken the geographic correlation one step further. To do this, they also controlled for exposure to pesticide use, air pollution, and other confounding factors (like heart disease) that vary geographically.

The authors found that variations in solar radiation alone (as a proxy for vitamin D) explained only about 30 percent of the U.S. geographic distribution in prostate cancer. By including temperature, precipitation, and pesticide use, as well as confounding factors such as unemployment and premature death due to heart disease, the authors were able to explain about 43 percent of the geographic variation.

How POPs Fit In

Their explanation for this improved correlation is that certain meteorological conditions acerbate our exposure to pesticides, including those POPs I mentioned above.

POPs, as defined by the Stockholm Convention, are chemicals like DDT and PCBs that:

  1. remain intact for many years;
  2. become widely distributed throughout the environment as a result of natural processes involving soil, water, and most notably air;
  3. accumulate in the fatty tissue of living organisms, including humans, and are found at higher concentrations at higher levels in the food chain; and
  4. are toxic to both humans and wildlife.

Why should men be more likely to be exposed to POPs in cold, snowy climates? A couple of reasons:

  • cold temperatures reduce the degradation of POPs allowing them to hang around longer; and
  • snow, the authors hypothesize, increases POP exposure by pulling these airborne pollutants out of the atmosphere thereby retaining them in the environment for continued exposure.

Of course, all this is highly speculative and I suspect will attract a lot of jokes about how global warming is the salvation for men and their prostates. I suspect a more rational approach would be to take the dangerous POPs off the market and out of circulation. Then, to borrow loosely from an old proverb, we could have our prostates and keep our climate too.

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