Experts at the American Institute for Cancer Research (AICR) recommend that new mothers breastfeed their children for at least the first six months. They cite convincing evidence that this practice offers cancer protection to both mother and child.

According to AICR, new mothers can directly lower their own risk of both pre- and post-menopausal breast cancer by breastfeeding. And children who are breastfed are less likely to become overweight or obese, which in turn lowers their risk of several common cancers that have now been convincingly linked to excess body fat.

The recommendation to breastfeed is one conclusion of the recently published AICR report, Food, Nutrition, Physical Activity, and the Prevention of Cancer: a Global Perspective. This comprehensive, 517-page report was the result of a five-year process involving nine independent teams of scientists, hundreds of peer reviewers, and 21 international experts who reviewed and analyzed over 7,000 large-scale studies on all aspects of cancer risk.

"The landmark AICR report concludes with 10 recommendations for cancer prevention, one of which deals exclusively with breastfeeding," said Karen Collins, MS, RD, AICR Nutrition Advisor. "AICR is the first major cancer organization to issue an official recommendation about breastfeeding."

The full AICR recommendation reads: It's best for mothers to breastfeed exclusively for up to six months and then add other liquids and foods.

Panel: Evidence on Breastfeeding Is "Convincing"

The AICR Expert Panel reviewed data from 98 studies on lactation and breast cancer risk, and concluded that the evidence linking lactation to lower risk for both pre- and post-menopausal cancer is convincing. A grade of convincing means that the evidence met the panel's strictest criteria; other grades included "probable," "limited, but suggestive," "limited, but no conclusion possible" and finally "substantial effect on risk unlikely." (Evidence that lactation reduces risk of ovarian cancer was judged "limited, but suggestive.")

Clinically speaking, the kind of breast cancer women get before menopause is different than the kind women get after menopause. Researchers now know that the two kinds of breast cancer have different root causes which are influenced by things like diet, body composition and physical activity in different ways.

"The fact that any single factor protects against both pre- and post-menopausal breast cancer is big news," said Collins. "The AICR expert panel looked at a host of variables associated with diet, nutrition, weight and activity, and lactation was the only one found to lower risk of breast cancer throughout a woman's life."

The most likely reason lactation lowers risk has to do with hormonal changes associated with breastfeeding, which delay the return of a new mother's menstrual cycle. Women who experience fewer menstrual cycles over their lifetime tend to have lower risk for breast cancer.

Breastfeeding also causes physical changes to breast cells that may make them more resistant to the kind of mutations that can lead to cancer; this is also thought to play a role in protection.

Panel: Babies Receive Cancer Protection, Too

According to the AICR report, breastfeeding a child probably reduces the chances that child will be overweight for at least the early years of childhood. This is important, because excess body fat in childhood tends to carry over into adulthood, and excess body fat is a convincing cause of six common cancers: colon, kidney, pancreas, endometrium, adenocarcinoma of the esophagus and post-menopausal breast cancer.

Why does breastfeeding seem to protect against excess fat? Breastfed infants tend to have a slower growth pattern than babies fed from a bottle. Some experts believe that the lower protein content of breast milk helps "program" an infant's body composition in ways that make obesity less likely later on. Substances that pass from mother to baby may also play a role, such as the appetite-regulating hormone leptin. Finally, because breastfed babies are not encouraged to "finish the bottle," they may learn to self-regulate their calorie intake in ways more closely suited to their body's needs.

Breastfeed "Exclusively," if Possible

Americans seem to be heeding this advice, at least in part. Rates of breastfeeding in the U.S. are on the rise - according to the Center for Disease Control, nearly 74 percent of women who gave birth in 2004 started breastfeeding.

But to maximize the health benefits to both mother and infant, the AICR panel recommends breastfeeding "exclusively" for the first six months. This means the infant should ideally receive no other food or drink (including water) at all during that time. But the CDC figures show that only 11 percent of women who gave birth in 2004 were breastfeeding exclusively at the six-month mark.

The longer babies receive breast milk exclusively, the longer they receive immune benefits and good nutrition (without excess calories.) At about the six-month mark, however, babies begin to require additional sources of nutrition, so other foods should be added. "In terms of anti-cancer benefits for both mother and infant, the longer breastfeeding continues, the better - within reason," said Collins.

The AICR experts stress that mothers who choose not to breastfeed can make other lifestyle choices about diet, weight and activity level that will lower risk for themselves and their baby. Visit for comprehensive advice about lowering risk.

AICR's recommendation to breastfeed reflects a new direction in cancer prevention research called the life-course approach, which concerns itself with the impact of early life events on cancer risk much later on.

The American Institute for Cancer Research (AICR) is the cancer charity that fosters research on the relationship of nutrition, physical activity and weight management to cancer risk, interprets the scientific literature and educates the public about the results. It has contributed more than $82 million for innovative research conducted at universities, hospitals and research centers across the country. AICR has published two landmark reports that interpret the accumulated research in the field, and is committed to a process of continuous review. AICR also provides a wide range of educational programs to help millions of Americans learn to make dietary changes for lower cancer risk. Its award-winning New American Plate program is presented in brochures, seminars and on its website, AICR is a member of the World Cancer Research Fund International.

American Institute for Cancer Research