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TUESDAY, March 9 (HealthDayNews) -- A new study on anorexia sheds light on why women in developing countries have lower incidence of breast cancer than other women: Diet is the key.

Studies with animals have found that when they eat substantially less than normal, they live longer and have fewer diseases, including breast tumors.

It is also known that women in developing countries have significantly lower rates of breast cancer, says lead researcher Dr. Anders Ekbom, a professor of epidemiology at the Karolinska Institute in Stockholm, Sweden.

To discover if these two facts were related, Ekbom and his colleague, Dr. Karin Michels from the Obstetrics and Gynecology Epidemiology Center at Brigham and Women's Hospital in Boston, decided to study breast cancer among women with anorexia.

They report their findings in the March 10 issue of the Journal of the American Medical Association.

Anorexia nervosa is a psychological disorder in which people don't eat because they are under the delusion that they are too fat despite being abnormally thin. The problem affects both women and men, but mostly women in their teens.

"Anorectic young women are similar to women in the Third World, where they don't have an abundance of food," Ekbom says.

Ekbom and Michels collected data on 7,303 Swedish women who were hospitalized for anorexia nervosa from 1965 to 1998. At the time of hospitalization, the women were all under age 40.

The researchers then compared this data with entries in the Swedish Cancer Registry and the Swedish Death Registry. They also looked for records of these women in the Swedish Fertility Registry.

Ekbom and Michels found that, compared to women in the general population of Sweden, the women with anorexia nervosa had 53 percent fewer cases of breast cancer.

When they looked at women who had at least one child, they found their risk of breast cancer was reduced by 76 percent. For women who had not had children, the risk was reduced by 23 percent.

"The time window when diet has an effect on breast cancer is when women are young -- around puberty," Ekbom says.

He speculates that the drastically lower food intake when these women were young continued to protect them as they aged. However, the reason having children so dramatically reduced the cases of breast cancer among these women is not known, Ekbom adds.

"Perhaps in developed countries this [higher breast cancer rate] is an additional price we pay for our society if we are going to feed our teens as much as we do today," Ekbom says.

However, this is not a public health message, he adds. And girls should not become anorexic to prevent breast cancer.

Dr. David L. Katz, the director of the Yale Prevention Research Center at the Yale University School of Medicine, says "there are many plausible mechanisms by which caloric restriction could reduce cancer risk in general, and breast cancer risk in particular."

Among them are "reduced metabolic demand and lower rate of mutation and cell turnover, as well as reduced hormone production," he says.

He cautions that the practical implications of this research are limited. "Were rates of anorexia to rise as women seek a means to lower breast cancer risk, it is very likely that more harm than good would result," he says.

Katz advises that moderation of calorie intake to keep weight at ideal levels would have an enormous public health benefit, including reducing the risk of breast and other cancers.

"Progress toward this well-supported goal, rather than something more extreme, less well-justified and potentially dangerous, should clearly be our priority," he says.

More information

The American Cancer Society has more information on risk factors for breast cancer, and the National Association of Anorexia Nervosa and Associated Disorders can tell you more about anorexia.

(SOURCES: Anders Ekbom, M.D., Ph.D., professor, epidemiology, Karolinska Institute, Stockholm, Sweden; David L. Katz, M.D., M.P.H., director, Yale Prevention Research Center, Yale University School of Medicine, New Haven, Conn.; March 10, 2004, Journal of the American Medical Association)

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