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Right Mix of Diet and Sun May Cut Breast Cancer Risk

Study suggests fatty food alone isn't culprit in disease

TUESDAY, Jan. 8, 2002 (HealthDayNews) -- The correct combination of diet, alcohol and sunlight may reduce a woman's risk of breast cancer, a new study suggests.

Experts have been debating the link between breast cancer and diet for decades, with no firm conclusions other than the observation that people with high-fat diets have a higher rate of mortality from the disease. However, the link has not been borne out in all studies.

In this study, William Grant, an independent researcher based in Newport News, Va., speculated that a high-fat diet alone wasn't responsible for higher rates of cancer. Instead, he thought, it was a variety of factors somehow related to fat.

"I said, 'Let's look at various factors together and see how they interact,'" says Grant. He gathered data on breast cancer mortality rates, diet and latitude from 35 countries, and dumped all the information into his computer. He then had the computer analyze the interplay between animal products as a percentage of total calories, alcohol and fish intake, and ultraviolet B exposure, as indicated by latitude.

The results appear in the Jan. 1 issue of the journal Cancer.

As it turns out, women who get more of their daily calories from animal products and less from vegetables over their lifetime have a higher mortality rate from breast cancer. Later in life, alcohol intake appears to increase risk, while fish intake and exposure to sunlight appear to reduce it. What's more, the mix of these factors accounted for 80 percent of the variance of breast cancer mortality rates between countries.

Digging a little deeper, Grant realized the common link between all these factors was an effect on estrogen and insulin growth factor (IGF-1), both of which are identified as possible risk factors for breast cancer.

"Every successive generation has more breast cancer, and that's because they get more into American diets, and more into it when they're young," says Grant. "If you're a person growing up and consume more concentrated protein and fat, you will grow faster and taller and will reach menstruation earlier -- and therefore have more lifetime supply of estrogen."

Protein also turned out to be more important than fat because it stimulates the production of IGF-1, says Grant. The average U.S. diet derives about 32 percent of its calories from animal products, compared with about 17 percent in Japan.

Meanwhile, alcohol is thought to increase the effect of estrogen, while fish reduces inflammation (a crucial factor in detecting tumors) and often contains vitamin D, which has been shown to reduce breast cancer risk. Exposure to ultraviolet B radiation also produces vitamin D.

Should you abandon the meat, give up alcohol, eat fish for breakfast, and head to the beach? Not yet, says Grant.

He notes that his theory, however intriguing, is still not proven.

"What I've done is presented a hypothesis paper that says diet in youth is very important, and later it's fish and alcohol and sunshine," says Grant, who is an atmospheric scientist but who has also published several papers on medical issues. "My model integrates much of what is already in the literature."

Grant suggests it's now up to professional epidemiologists to study the phenomenon.

Other experts agree wholeheartedly.

"Comparisons across countries of factors that may reduce breast cancer risk are limited in that they cannot take into account many important factors, such as age at birth of the first child, number of children, use of hormones…, and consequently these studies serve mostly to guide future research rather than to provide definitive information to the public," says Dr. Michael Thun, head of epidemiologic research for the American Cancer Society.

"It's a hypothesis, as opposed to anything definite," adds Dr. Clifford Hudis, chief of the breast cancer medicine service at Memorial Sloan Kettering Cancer Center. "I think he's got a newer and more refined study model for the risk, incorporating a variety of factors, and his findings are consistent with many earlier studies. But the gold standard for medical science is the prospective study."

What To Do

Linda Frame, senior clinical advisor for the Susan G. Komen Breast Cancer Foundation, says a healthy lifestyle is still recommended: "This includes regular exercise and eating right, which is basically increasing the number of fruits and vegetables you have each day and decreasing fat. We know through other studies that these measures lead to overall optimal health."

Both the Susan G. Komen Breast Cancer Foundation and the American Cancer Society have a wealth of information on breast cancer.

SOURCES: Interviews with William Grant, Ph.D., independent researcher, Newport News, Virginia; Michael Thun, M.D., head, epidemiologic research, American Cancer Society, Atlanta; Clifford Hudis, M.D., chief, breast cancer medicine service, Memorial Sloan Kettering Cancer Center, New York City; Linda Frame, R.N., senior clinical advisor, Susan G. Komen Breast Cancer Foundation, Dallas; Jan. 1, 2002, Cancer
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