The Link between Sunlight Exposure and Colorectal Cancer
November 16, 2009
In the 1980′s, Drs. Cedric Garland and Frank Garland observed that those who lived in sunny areas had a reduced risk of dying from colon cancer. A map view of the United States, with an overlay of colorectal cancer mortality data, clearly illustrates this relationship. The geographic pattern shows significantly lower rates in areas that have greater sunlight intensity. In contrast, death rates tend to increase with increasing latitude, or distance from the equator.
The map also reveals that the northeastern states have higher rates compared to the northwestern states, even though the latitudes are similar. At first glance, this appears to defy the pattern However, further inspection reveals that this
discrepancy is due to atmospheric variation. The Northeast has a thicker ozone layer and more air pollution. Both factors decrease the amount of available sunlight. The Garlands proposed that vitamin D could explain this observation, since most people get the majority of their vitamin D from sunlight exposure. Later, evidence began to accumulate that linked blood levels of vitamin D to colon cancer.
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