Significant Weight Gain During Pregnancy May Impact Breast CancerRisk After Menopause (dateline August 17, 2002)
A new study finds that women who gain a large amount of weight during pregnancy face a higher risk of developing breast cancer after they reach menopause. The researchers attribute the increased breast cancer risk to a higher amount of estrogen that is produced in fat cells, which may be especially harmful as the breast undergoes rapid changes during pregnancy. Still, the researchers acknowledge that the risk of breast cancer appears to be relatively small for women who gain a significant amount of weight during pregnancy. Furthermore, women who retain the extra weight after pregnancy tend to be at higher risk of post-menopausal breast cancer than those who lose the excess pounds after childbirth.
Researcher Leena Hilakivi-Clarke, PhD presented the study findings at the annual meeting of the American Association for Cancer Research (AACR), held in April 2002. To conduct the study, Dr. Hilakivi-Clarke and her team analyzed medical records from over 27,000 Finnish women. The first analysis consisted of 17,360 women, including 98 women who developed pre-menopausal breast cancer at an average age of 47. The second analysis was made up of 3,209 women, 185 of whom developed post-menopausal breast cancer at an average age of 58.
Based on their analyses, the researchers concluded that women who gained more than 38 pounds during pregnancy faced a 40% greater risk of developing post-menopausal breast cancer, compared with women who gained less weight. Weight gain during pregnancy was not associated with an increased risk of breast cancer before menopause.
"We also found that women who retain the added pounds after pregnancy are at the greatest risk. These additional pounds may induce changes in breast tissue that increase susceptibility to breast cancer in later life," said Dr. Hilakivi-Clarke, as quoted in an AACR news release. "Overall, the increased risk due to pregnancy weight gain is modest equivalent to the increased risk from obesity after menopause."
According to Dr. Hilakivi-Clarke, previous data have found that women who gain a large amount of weight during pregnancy have higher estrogen levels than women who gain less weight. The study suggests that the higher a woman's estrogen levels, the higher her risk of developing post-menopausal breast cancer.
Though the study found that more than 38 pounds gained during pregnancy increased breast cancer risk, Dr. Hilakivi-Clarke said that obstetricians recommend gaining 25 to 35 pounds during pregnancy and that this amount of weight gain was not associated with a higher risk of breast cancer, before or after menopause.
Despite this latest study, the link between weight and breast cancer risk remains controversial. Several small studies suggest that overweight (obese) women who gained their excess weight as adults are at an increased risk of developing breast cancer, but women who have been overweight since childhood are not at any significantly higher risk. Also, overweight women who take hormone replacement therapy may be at greater risk of developing breast cancer. In an interview with the Associated Press, Dr. Eugenia Calle, Director of Analytic Epidemiology at the American Cancer Society, said that significant weight gain during pregnancy may not be any more harmful than weight gain in general.