Being low on high-density lipoprotein (HDL) cholesterol, the "good" kind of cholesterol, has been linked to all sorts of diseases, most commonly heart attack and stroke. People who are overweight tend to have lower levels of HDL cholesterol and, as people around the world push the scales higher and higher, a simultaneous increase in breast cancer has some worried. Researchers from Norway decided to try to find out if a low HDL cholesterol level could increase the risk for breast cancer.

What the researchers wanted to know: Are women with low levels of HDL cholesterol more likely to get breast cancer?

What they did: The researchers followed-up on women who took part in a project that analyzed the health of more than 38,000 women in Norway from 1977 to 1983, and again from 1985 to 1987. The women answered questions about their health, diet, exercise, and menopausal status, were measured and weighed on a scale, and had a blood sample drawn. After the initial surveys, the women were tracked through Norwegian government statistics and the rate of cancer, other illnesses, death, or emigration was recorded.

What they found: In the 17 years of average follow-up, 708 of the women developed breast cancer. Women with high HDL levels were 25 percent less likely to get postmenopausal breast cancer than women with low HDL cholesterol. The difference was even bigger for women who were overweight. Overweight women with high levels of HDL cholesterol were 66 percent less likely to develop postmenopausal breast cancer than overweight women with low levels.

What it means to you: High HDL cholesterol has been credited with preventing other diseases, but this study is one of the first to show that it can affect breast cancer. Just in case you needed one more reason to exercise, quit smoking, and watch what you eat.

Caveats: The data asked women about their health in the initial surveys but not after that, and many things could have affected their health after the initial surveys were completed in the 1980s. For example, the data do not take into account whether women began taking hormone therapy, which has been shown to increase risk for breast cancer. The authors tried to adjust for some of these unknowns in their data, but could not be exact.

Find out more: The American Heart Association has an excellent page that explains the difference between good and bad cholesterol.

The Susan G. Komen Breast Cancer Foundation has a site on risk factors for breast cancer.

And, if you want to learn more about Norway by the numbers, check out Statistics Norway (don't worry, it's in English)

Wondering what the weather's like right now at the Norway's University of Tromsø, way above the Arctic Circle, where some of the researchers are based? Go to weather.cs.uit.no.

Read the article: Furberg, Anne-Sofie et al. "Serum High-Density Lipoprotein Cholesterol, Metabolic Profile, and Breast Cancer Risk." Journal of the National Cancer Institute. Aug. 4, 2004, Vol. 96, No. 15, pp. 1152-1160.

Abstract online: http://jncicancerspectrum.oupjournals.org