Breastfeeding protects against cancer, study confirms

Globe and Mail Update 
POSTED AT 6:30 PM EDT Thursday, July 18, 2002

Women in the Western world could sharply decrease their chances of developing breast cancer by having more children and breastfeeding longer, according to a massive new international study teeming with tricky social implications.

Researchers have long considered reasons why breast cancer rates in developed countries dwarf those in poorer nations. While childbearing is known to offer a protective benefit, it was unclear if breastfeeding itself provides a significant defense against the disease.

But after crunching numbers and dissecting data from nearly 150,000 women in 30 countries, researchers now confirm that if Western women breastfed each of the few babies they do have for even six months longer, 25,000 cases of breast cancer could be prevented each year or 5 per cent of all breast cancer cases in industrialized countries.

"We have shown that these factors (childbearing and breastfeeding) alone account for the high rates of breast cancer in more-developed settings," said Valerie Beral, one of the study leaders at the Cancer Research UK Epidemiology Unit in Oxford.

The study, published today in the British science journal Lancet, found that women who developed breast cancer had spent an average of 10 months breastfeeding in their lives. And women who did not develop the disease had breastfed an average of 16 months.

The researchers concludes that a woman’s relative risk of breast cancer drops by 4.3 per cent for every 12 months she has spent breastfeeding in her life, in addition to a 7 per cent drop with each birth.

Yet just as Canada’s 2001 census shows women having fewer children than ever before - an average of 1.5 - the researchers themselves acknowledge that their findings do not easily fit the dynamics of modern society, where women are equal contributors to the labour force and maternity leaves are limited.

"To expect that substantial reductions in breast-cancer incidence could be brought about today by women returning to the pattern of childbearing and breastfeeding that typified most societies until a century or so ago is unrealistic," the study authors write.

They even suggest developing a therapy to somehow mimic the protective benefits of breastfeeding - although the actual anti-cancer effects of childbearing and breastfeeding remain a mystery.

Richard Gallagher, head of Cancer Control Research at the B.C. Cancer Agency, which contributed data from more than 2,000 Canadian women to the project, stressed that "In a modern Western society, this study is not an exhortation to go out and have six or seven kids ... but any breastfeeding is better than none and more breastfeeding is better than some."

The study also raises questions about whether the incidence of breast cancer is linked to the duration of maternity leaves. Dr. Gallagher agreed that it’s valid to consider whether the high rates of the disease in the U.S., for example, is related to their short paid maternity leaves of just six weeks.

"There’s a wake up call for governments here, for each birth we reduce breast cancer risks ... with each year of lactation there’s a reduction of risk," he said. "It’s pretty tough to breastfeed when you're at work."

Donna Stewart, chair of women’s health for the University Health Network and the University of Toronto, cautions against over-interpreting the study results., She pointed out that the most dramatic protective benefit accumulate after the third child. "You’ve got to be a real breeder to benefit," she said.

The study analyzed information from 50,302 women with breast cancer and 96,973 women without breast cancer in 47 studies from 30 countries. The major findings included:

  • Women with breast cancer had an average of 2.2 children. Women without the disease had an average of 2.6.
  • Women who developed breast cancer had a lifetime duration of breastfeeding of about 10 months. Women who did not develop the disease had breastfed an average of 16 months during their lifetime.
  • For every 100 women up to the age of 70 in the developed world, where children are breastfed for an average of three months, there were between five to seven cases of breast cancer in 1990.
  • In Asian and African countries, where a child is breastfed for an average of 24 months, there were only one to two cases of breast cancer for every 100 women.
  • Researchers also note that as women in developing countries have fewer children, their breast cancer rates are rising.