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Weight Gain Increases Breast Cancer Risk
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Kroenke CH, Chen WY, Rosner B, Holmes MD. Weight, Weight Gain, and Survival After Breast Cancer Diagnosis. J Clin Oncol. 2005 Jan 31; [Epub ahead of print]
http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=15684320
Channing Laboratory, Department of Medicine, Brigham & Women's Hospital, and Harvard Medical School; and Department of Medical Oncology, Dana-Farber Cancer Institute, Boston, MA.
ABSTRACT
PURPOSE: To determine whether weight prior to diagnosis and weight gain after diagnosis are predictive of breast cancer survival.
METHODS: Patients included 5,204 Nurses' Health Study participants diagnosed with incident, invasive, nonmetastatic breast cancer between 1976 and 2000; 860 total deaths, 533 breast cancer deaths, and 681 recurrences (defined as secondary lung, brain, bone, or liver cancer, and death from breast cancer) accrued to 2002. We computed the change in body mass index (BMI) from before to the first BMI reported >/= 12 months after the date of diagnosis. Cox proportional hazards models were used to evaluate associations of categories of BMI before diagnosis and of BMI change with time to event. We stratified by smoking, menopausal status, and breast cancer-related variables.
RESULTS: In multivariate-adjusted analyses, weight before diagnosis was positively associated with breast cancer recurrence and death, but this was apparent only in never smokers. Similarly, among never-smoking women, those who gained between 0.5 and 2.0 kg/m(2) (median gain, 6.0 lb; relative risk [RR], 1.35; 95% CI, 0.93 to 1.95) or more than 2.0 kg/m(2) (median gain, 17.0 lb; RR, 1.64; 95% CI, 1.07 to 2.51) after diagnosis had an elevated risk of breast cancer death during follow-up (median, 9 years), compared with women who maintained their weight (test for linear trend, P = .03). Associations with weight were stronger in premenopausal than in postmenopausal women. Similar findings were noted for breast cancer recurrence and all-cause mortality.
CONCLUSION: Weight and weight gain were related to higher rates of breast cancer recurrence and mortality, but associations were most apparent in never-smoking women.
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COMMENTS:
The recurrences were strongest in women who had not yet had the menopause.
There are two other interesting points in this study:
Firstly, in trying to explain a possible relationship between overweight and increased risk, the researchers suggest thatobesity may promote cancer by raising the body's levels of sex hormones such as oestrogen, particularly in postmenopausal patients. But there might be another explanation: Weight gain is caused by a diet based on carbohydrates – starchy foods and '5 portions of fruit' etc. These foods also compromise our immune system, which reduces the body's ability to fight cancer.
It's also noticeable that, in this study, women who had never smoked were at greater risk than smokers. I remember some years ago a study finding that, while drinking alcohol increased breast cancer risk, smoking reduced it. Although I cannot find the reference for this now, this latest study does seem to confirm the earlier one.
Last updated 5 February 2005
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