Eating lots of fish during and after pregnancy reduces daughters' risk of developing breast cancer

Mothers who eat foods rich in omega-3 fatty acids during pregnancy and while nursing, and who continue to feed their babies such a diet after weaning, may reduce their daughters' risk of developing breast cancer later in life dramatically, according to research presented here today at the 96th Annual Meeting of the American Association for Cancer Research.

Either maternal or post-weaning dietary consumption of this type of fat – that is, taking in omega-3 fatty acids through food or supplements at any point in life from conception to at least puberty – also could reduce the incidence rate for breast cancer in female offspring significantly.

Conversely, mothers' consumption of omega-6 fats commonly found in Western diets could increase their daughters' risk of breast cancer.

"Diet matters, Mom," said W. Elaine Hardman, Ph.D., an assistant professor in the Division of Functional Foods at the Pennington Biomedical Research Center, Louisiana State University, Baton Rouge. "Inadvertently, we may be setting up our daughters to develop breast cancer 50 years from now."

Both omega-6 and omega-3 fatty acids are essential for human health; however, particularly in the Western hemisphere, omega-6 fatty acids far exceed omega-3 fatty acids in the typical diet. Meat, eggs, poultry, cereals, breads, baked goods, most vegetable oils, and margarine are among dietary sources of omega-6 fatty acids.

Omega-3 fatty acids occur most commonly in fish – especially cold-water fish such as tuna, salmon and mackerel – as well as in canola and flaxseed oils, soybeans and nuts.

Hardman based her hypothesis on existing research showing that maternal diets containing high amounts of omega-6 fatty acids increase maternal estrogen levels; increased maternal estrogen, in turn, has been linked to an increased incidence of breast cancer among female offspring.

Meanwhile, many foods rich in omega-3 fatty acids are known to block the effects of estrogen and boost immunity.

Working with mice bred with a genetic predisposition to develop breast cancer, Hardman compared the incidence rates for the disease in offspring depending upon theirs and their mothers' relative consumption of diets either high in omega-6 fatty acids, or high in omega-3 fatty acids.

The genetic make-up of the female mice was such that all would develop hyperplasia; that is, to grow too many normal cells, in the mammary ducts, by three months of age. By six months, that hyperplasia would progress to mammary adenocarcinoma.

The mice were bred and the mothers were fed diets high in either omega-6 fatty acids or high in omega-3 fatty acids, both during the gestation period and while breast-feeding the female young. After the daughters were weaned, one group was placed on a high-omega-6 fatty acid diet, while the other was fed predominantly omega-3 fatty acids.

In Hardman's experiment, all the young exposed only to omega-6 fatty acids, in utero, in nursing and after weaning, showed mammary gland tumors by six months of age. Conversely, fewer than 60 percent of the female offspring who ate richly of high omega-3 fatty acids either maternally or post-weaning formed mammary tumors by the age of eight months. Those exposed to omega-3 fatty acids both maternally and after weaning had a tumor incidence rate of just 13 percent.

The beauty of the mouse model, Hardman explains, is the ability it gives researchers to collapse an entire life-span into a matter of months, instead of years. By using mice programmed genetically to develop tumors in the mammary glands eliminates the element of chance.

Harman has observed suppression of tumor growth with as little as two percent omega-3 fatty acids in the diet.

"A couple of servings a week may be enough," she said. "A quarter of a cup of walnuts constitutes one serving."

For pregnant women who are concerned about ingesting mercury in fish, Hardman recommends fish oil supplements, readily available in grocery, drug and health food stores. The fish oil in supplements is well purified.