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Posted online on January 31, 2005 on
www.jco.org.
Read the original study
A new study shows that women who are overweight prior to breast cancer
diagnosis, or who are lean but gain weight following diagnosis, are more
likely to have their disease return or to die of the disease. The study
will be published in the
Journal of Clinical Oncology (JCO).
To evaluate the relationship between weight gain and breast cancer
survival, researchers examined lifestyle and medical history information
of 5,204 breast cancer patients participating in the Nurses' Health
Study (NHS), a study of the health of 121,700 female nurses conducted
between 1976 and 2000.
Researchers used body mass index (BMI)—the ratio of a person's height in
meters to their weight in kilograms—to classify women as normal weight
(BMI of 18.5 to 24.9), overweight (BMI of 25 to 29.9), or obese (a BMI
above 30). Researchers also analyzed whether women gained, lost, or
maintained weight before and after diagnosis.
Researchers found that being overweight prior to diagnosis was
associated with poorer survival and that this was particularly evident
among women who had never smoked. Never smokers who had BMI of 25 or
higher at diagnosis were nearly twice as likely to die than women who
were normal weight.
Futhermore, women who gained weight after their breast cancer diagnosis
were also more likely to see have their disease return or to die, and
this risk increased as weight gain increased. Again, this was most
evident in women who had never smoked. Never-smoking women who gained an
average of 17 lbs were 1.5 times more likely to have their disease
return or to die during follow-up than women who maintained their
weight.
Researchers speculate that obesity may cause or worsen cancer by raising
the body's levels of sex hormones, such as estrogen. However, including
smokers in an analysis of weight and survival may mask the true
relationship between these factors because smoking may promote the
formation of less biologically active estrogens and has been related to
lower levels of weight.
Although other studies have addressed the link between obesity and
breast cancer survival, researchers noted that no prior studies have
separated smokers from nonsmokers, and underscored that more research
needs to be done to better explain how weight and smoking influence
survival. |
