First study to focus on younger pre-menopausal women finds anincreased risk for hormone receptor-positive breast tumors
by Craig Weatherby

The results of an innovative study affirm the dangers of excessive enjoyment of red meat. While they don't mean that women can't eat red meat safely, these findings indicate that it may make sense to practice moderation and stick to grass-fed beef.

The authors of the study
led by Harvard's Eunyoung Cho, Sc.D. (pictured at left)noted that while high red meat intake is considered conducive to breast cancer, none of the previous studies included substantial numbers of young, pre-menopausal women.

Key Points
  • Rates of hormone receptor-positive breast tumors are rising in the U.S.
  • Pre-menopausal women's risk of hormone receptor-positive cancer was twice as high if they ate more than one and one-half servings of red meat a day, compared with those who ate three or fewer servings per week.
  • Red meat consumption did not affect their risk of breast cancer overall or hormone-receptor-negative cancers.
  • “Hormone receptor-positive” tumors in which women's sex hormones (estrogen and progesterone) bind to receptor proteins on the surfaces of the tumor cells.
  • “Hormone receptor-negative” tumors in which this does not occur.
This data gap explains why, when Dr. Cho's group set out to look for any links between red meat consumption and breast cancer, they focused on pre- menopausal women: specifically, 90,659 members of the Nurses' Health Study II whose average age was 36 at the outset of the study.

In addition, the Boston-based team were looking for any differences in risk between the two major types of breast cancer:

As they said, “The association between red meat intake and breast cancer is unclear, but most studies have assessed diet in midlife or later. Although breast tumors differ clinically and biologically by hormone receptor status, few epidemiologic studies of diet have made this distinction.”

Any difference in the degree of breast cancer risk posed by high red meat intake is of special interest because, as the Boston team wrote, “… the incidence of hormone receptor-positive tumors has been increasing in the United States, especially among middle-aged women.”

Dr. Cho and her colleagues—who included legendary Harvard nutrition researcher Walter C. Willett, M.D.--followed the women from 1991 through 2003.

The women completed an initial diet questionnaire in 1989, and responded to subsequent food intake surveys in 1991, 1995 and 1999.

Every two years they reported whether or not they had developed breast cancer. Any reported cases were confirmed through hospital records and pathology reports.

Only pre-menopausal women never diagnosed with cancer were included in the data, and any who experienced menopause or an ovariectomy during the 12 years of the study were not.

By the end of the study, the women reporting the highest red meat intake were not at significantly greater risk for breast cancer overall or for hormone-receptor-negative cancers, but did show an increased risk of hormone receptor-positive cancer.

In fact, the risk of hormone receptor-positive cancer was twice as high among women who ate more than one and one-half servings of red meat a day, compared with those who ate three or fewer servings per week.

Why would red meat cause hormone receptor-positive breast cancer? The researchers noted three reasons:
  • Cooked or processed red meats contain known cancer-causing compounds that increase mammary tumors in animals and are suspected of causing breast cancer in humans.
  • Cattle in the United States are treated with hormones to promote growth, which could influence breast cancer risk.
  • The form in which iron occurs in red meat may promote tumors.
It's probably safer to stick to certified grass-fed beef, whose fat profile leans heavily toward anti-cancer omega-3s, with many fewer cancer-fueling omega-6 fats than occur in standard, grain-fed beef.

  • Cho E, Chen WY, Hunter DJ et al. Red Meat Intake and Risk of Breast Cancer Among Premenopausal Women. Arch Intern Med. 2006;166:2253-2259.