"If women gained more than 22 pounds, they were 83% more likely to die of breast cancer than those who gained or lost less than 5 pounds," says Hazel B. Nichols, a doctoral student in epidemiology at Johns Hopkins Bloomberg School of Public Health in Baltimore.
At the same meeting, other researchers reported that women with breast cancer who had high insulin levels, which tend to occur in heavier women, are also at an increased risk of death.
Weight Gain-Death Risk Study
In the first study, Nichols and her colleagues evaluated nearly 4,000 women who had been diagnosed with invasive breast cancer in the years 1988 to 2001.
They asked the women to report their weight, weight gain, physical activity, diet, medication history, and quality of life, following them up for more than six years.
When the researchers looked at weight status and death, the risk of breast cancer death was more than twice as high among those women who were obese after the diagnosis (who may or may not have been obese before) compared with those who were normal weight during the follow-up, Nichols found.
Obesity is defined as having a body mass index or BMI of 30 or above. A 5-foot-4 woman who weighs 175 has a BMI of 30.
"We do see a trend, in general, that there is increased risk of breast cancer mortality with increasing body mass index," Nichols tells WebMD.
Being overweight but not obese was not as risky, Nichols says. Overweight women with a BMI of 25 to 29.9, she found, were 1.3 times more likely to die from their breast cancer, an increased risk that could have been due to chance in the study.
The study did have an important limitation, Nichols tells WebMD. "We did not have extensive information on other medical conditions in later age," she says. "The extremes in risk may be related to other medical conditions that affect your risk of dying."
Insulin-Breast Cancer Death Link
In a second study, women with invasive breast cancer and high blood levels of C-peptide, a marker of insulin secretion, were more likely to die than women with lower C-peptide levels, according to Melinda Irwin, PhD, MPH, an assistant professor at the Yale University School of Public Health in New Haven, Conn.
"Women who are heavier tend to have higher C-peptide or higher insulin levels," she tells WebMD.
Her team followed 689 women enrolled in a National Cancer Institute initiative study known as the HEAL (Health, Eating, Activity and Lifestyle) study. All had breast cancer, but not type 2 diabetes. They were all postmenopausal, either naturally or due to chemotherapy.
Irwin's team monitored health status periodically, from six months after the diagnosis until 2004 or until the patient's death, taking blood samples to measure their C-peptide levels.
The younger the women were, the more dramatic the risk of death linked with high C-peptide, she says. Women with high C-peptide levels who were ages 40 to 55 when they provided the blood samples had a nearly five times increased risk of breast cancer death compared with the same ages of women who had lower C-peptide levels.
Perspective on Weight Gain and Breast Cancer
The new findings echo previous research that has found a link not only between excess weight and death in breast cancer patients but also excess weight and breast cancer recurrence.
Excess weight can also increase risk of getting breast cancer, other research has found, at least for postmenopausal women. "In the postmenopausal period, adipose tissue is the primary source of estrogen," Nichols says. "So the greater BMI in postmenopausal women may increase exposure to circulating estrogen [thus "feeding" the cancer]."
The message is clear, Irwin says. Paying attention to diet and exercise and trying to maintain a healthy weight is crucial.