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Observational studies of large population groups have turned up two simple ways to reduce the risk of endometrial cancer: suntans and coffee. Both studies were performed in Sweden, which has one of the world's highest per capita coffee consumption rates. Overweight and obese women had the largest risk reductions.
The suntan study, by Dr. E. Epstein and coworkers, included 17,822 post-menopausal women followed for an average of 15.5 years. Women who used tanning beds at least three times per year had a 40 percent reduction in endometrial cancer. In Sweden, tanning bed use is common in the winter. Outdoor sunbathing in the summer, either in Sweden or abroad, had less effect. The authors suggested that improved vitamin D levels in winter were the cause of the reduced cancer risk. When the data were adjusted for body mass index or physical activity, the benefit of tanning beds was a 50 percent reduction in endometrial cancer risk.
The coffee study, by Dr. Emilie Friberg and coworkers, included 60,634 women followed for an average of 17.6 years. Overall, each cup of coffee per day reduced the risk of endometrial cancer by 10 percent. Overweight women saw a decreased risk of 12 percent for each daily cup of coffee, while obese women saw a decreased risk of 20 percent.
There are four proposed mechanisms for coffee's effect:
1.Coffee has been shown to affect glucose metabolism and reduce the risks of hyperinsulinism and type 2 diabetes. The endometrium has insulin receptors which stimulate the growth of stromal cells.
2.Caffeine has been linked to lower estrogen levels. Decaffeinated coffee is rare in Sweden, so coffee and caffeine were highly correlated in this study.
3.Coffee contains phytoestrogens which may affect the endometrial cells.
4.Coffee contains antioxidants which may reduce the risk of cancer in general.
Both studies confirmed previous reports that obesity and estrogen exposure are major risk factors for endometrial cancer. Unexpectedly, cigarette smoking decreased the risk. The mechanism for this effect is not known.
The American Cancer Society estimates that over 43,000 women per year develop endometrial cancer in the United States.