Eating red meat may raise a woman's risk of a common type of breast cancer, a new study suggests.

Women who ate more than 1½ servings of red meat per day were almost twice as likely to develop hormone-related breast cancer as those who ate fewer than three portions per week, one study found.

"Our study may give another motivation to reduce red meat intake." -Study co-author Eunyoung Cho

The study was led by doctors at Harvard Medical School, who tracked the diets and health of more than 90,000 women.

Participants in the Nurses' Health Study were 26 to 46 years old when they enrolled about two decades ago.

They filled out diet questionnaires in 1991, 1995 and 1999, and were divided into five groups based on how much red meat they said they ate. Researchers checked on their health for 12 years on average and confirmed breast cancer diagnoses with medical records.

Meat consumption was linked to a risk of developing tumours whose growth was fuelled by estrogen or progesterone — the most common type — but not to tumours that grow independently of these hormones.

The women who ate more red meat were more likely to smoke and be overweight, but when the researchers took those factors into account, they still saw that red meat was linked with an increased risk of breast cancer.

Words of caution

Earlier studies have found that obesity raises the risk of breast cancer and that red meat raises the risk of colorectal cancer.

"Our study may give another motivation to reduce red meat intake," said study co-author Eunyoung Cho.

However, Dr. Anne McTiernan of the Fred Hutchinson Cancer Research Center in Seattle cautioned that the findings rely on women's recall of what they ate — an inexact way to measure diet.

"A 16-ounce steak and a three-ounce piece of meat are counted the same. People are horrible at determining what is a real serving," said McTiernan, author of Breast Fitness, a book on reducing cancer risk.

It may be wise to cut down on red meat because of its fat and calorie content, McTiernan said, but "this isn't a reason to become a vegetarian if you weren't planning to do that already."

The study was published in Monday's Archives of Internal Medicine.