Does 10 to 15 minutes of sun per day decrease a woman's chances of breast cancer? That's the claim of Esther John, a researcher at the Northern California Cancer Center, made at a recent Department of Defense conference.
John studied women with, and women without breast cancer, and reported those who were the least sun-exposed (based on where they lived and how often they played or worked in the sun) had about a 70 percent increase in breast cancer risk.
But John should know better.
First, case-control epidemiologic studies like hers are simply incapable of reliably detecting increases in risk of less than 100 percent.
Case-control epidemiology is fine for detecting large increases in the risk of rare diseases, like smoking and lung cancer, but not small increases of relatively common diseases.
For example, heavy smokers have 20 times the rate of lung cancer as nonsmokers, who get lung cancer at a rate of about 1 in 10,000. Here, John says the least sun-exposed women have only about 1.7 times the rate of breast cancer as the most sun-exposed. And breast cancer can be relatively common; it occurs in elderly women at a rate of about 1 in 10.
So it's unlikely that she reliably detect such a "fine" result with such a "crude" tool.
Lastly, John's theory is that vitamin D, which is produced by the body when exposed to sunshine, is what reduces breast cancer risk. But studies have so far produced inconsistent results on the cancer risk-reducing role of vitamin D. Such inconsistency may mean that there is no detectable effect.
Breast cancer can't be prevented. But it can be cured (at a rate in excess of 90 percent!) if detected early enough. Women need to know that... not more junk science.
Material presented on this home page constitutes opinion of the author.
Copyright © 1997 Steven J. Milloy. All rights reserved. Site developed and hosted by WestLake Solutions, Inc.