Setting a stage for cancer: another reason for women not to drink while pregnant.

Imbibing substantial amounts of alcohol during pregnancy can cause fetal alcohol syndrome, a condition characterized by birth defects ranging from abnormal facial features to severe neurological defects. New studies with rats indicate that a previously unrecognized risk to the fetus, cancer later in life, might come from even modest in utero exposure to alcohol.

Leena Hilakivi-Clarke of Georgetown University in Washington, D.C., fed alcohol to 30 pregnant rats each day during their latter two trimesters. Half consumed small amounts, such that 7 percent of their daily calories came from the alcohol. The other half consumed twice that quantity of alcohol. "These [amounts] are similar to those seen in low-to-modest alcohol drinkers ... and lower than those found to induce fetal alcohol syndrome," says Clarke in the June British Journal of Cancer. A third group of rats received no alcohol.

Three weeks after birth, the female rats exposed to alcohol in utero had significantly more terminal end buds--a type of breast tissue that can later form tumors--than did the rats that had not been exposed to alcohol, Clarke found.

Once the rats entered puberty, Clarke injected them with a cancer-causing chemical. Almost all the animals developed mammary tumors, but those whose mothers imbibed the most alcohol developed twice as many tumors as those whose mothers consumed no alcohol. The group exposed to the low dose of alcohol showed an intermediate number of tumors.

How alcohol might set the stage for cancer is not clear. Clarke speculates that alcohol accelerates the natural conversion of testosterone to estrogen in the womb. "Estrogen somehow programs the [breast tissue] so that, later on, it turns out to be more dense," says Clarke. Researchers have linked dense breast tissue in women to increased risk of breast cancer.

Most of the risk factors associated with breast cancer, including tissue density, birth weight, and the age at which menstruation begins, are ones that women can't easily control. And most choices about adult exercise and diet appear to be unrelated to breast cancer, says Karin Michels of Harvard Medical School in Boston. However, she notes, a woman's alcohol consumption slightly increases her breast cancer risk.

Michels and a growing number of breast cancer researchers are now focusing on the lifestyles of women from adolescence to just before menopause, with studies of fetal rats, Michels notes, Clarke is "looking even earlier in life."

The new study doesn't establish a link between a woman's alcohol consumption during pregnancy and breast cancer in her adult daughter, says Clarke, but the results ought to serve as a warning.

This isn't the first suggestion that fetal conditions can affect a person's health decades later. For example, many researchers have noted links between low birth weight and adult heart disease, stroke, osteoporosis, and diabetes.

For most pregnant women, one drink a month is not likely to affect their sons or daughters in later life, Clarke says. But considering the severity of problems already pegged to alcohol and the variation in responses to it, she adds, "there's no safe level" of consumption during pregnancy.