ONDON,
July 22 — The number of children women have and the time they breast-feed them
are important factors in their chance of developing breast cancer, new research
shows.http://www.nytimes.com/2002/07/23/health/23BABY.html
ONDON,
July 22 — The number of children women have and the time they breast-feed them
are important factors in their chance of developing breast cancer, new research
shows.
The study, published on Saturday in The Lancet medical journal, found that if women in the industrialized world breast-fed each of their children six months longer, they could reduce their chance of breast cancer 5 percent, even if they have strong family histories of the disease.
The study involved 200 researchers across the globe examining more than 47 studies that investigated a total of 150,000 women. The analysis of the pooled information was conducted by epidemiologists at Oxford University.
The theory that childbearing is linked to breast cancer dates from 1743, when an Italian researcher called the disease an occupational hazard of nuns, attributing their relatively high rate of breast cancer to their childlessness.
Breast cancer rates started to climb at the end of the 19th century. By the 1950's, scientists had established that the number of children a woman gave birth to was a factor in breast cancer.
In 1970, a study found that the age at which a woman had her first child was crucial, but that neither the number of children nor the breast-feeding habits were factors.
"Since that time, almost every study on breast cancer has confirmed that finding on age at first birth, but there's been a lot of confusion about whether the number of children and breast-feeding had an effect on breast cancer," said the leader of the new study, Valerie Beral, head of the Oxford epidemiology unit.
Confusion has remained, particularly about the role of breast-feeding, because individual studies have been too small to provide answers, she said.
The Oxford group started by looking at 20,000 women who had just one child and who had never breast-fed and comparing them with women who did not breast-feed but continued to have children.
"The risks go down the more children you have," Ms. Beral said. "Even if they'd never breast-fed, the risk of breast cancer went down by 7 percent for every additional child."
The researchers also found that regardless of the number of children the risk of breast cancer dropped 4.3 percent for every year the women breast-fed.
The level of protection was the same in all women, regardless of ethnic origin, drinking habits and age at menopause.
In the developed world, women have an average of two or three children and breast-feed each for two or three months.
A century ago, Western women used to have six or seven children and breast-feed each for two years, a pattern still dominant in many parts of the developing world.
Today, women in the industrialized world have a 6.3 percent chance of contracting breast cancer by age 70 compared with a 2.7 percent chance for their counterparts in poor countries.
Part of the reason is that women in poor countries typically have children earlier, at 18 or 19, compared with 23 or 24 in the developed world.
The study found that if women in developed countries had six or seven children instead of two or three their risk of breast cancer would decrease to 4.7 percent, from 6.3 percent.
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