Interaction between smoking and obesity and the risk of developing breast cancer among postmenopausal women

Juhua Luo, Kimberly Horn, Judith K. Ockene, Michael S. Simon, Marcia L. Stefanick, Elisa Tong, Karen L. Margolis

Research output: Contribution to journalArticlepeer-review

30 Scopus citations


Obesity is a well-established risk factor for postmenopausal breast cancer. Recent studies suggest that smoking increases the risk of breast cancer. However, the effect of co-occurrence of smoking and obesity on breast cancer risk remains unclear. A total of 76,628 women aged 50-79 years enrolled in the Women's Health Initiative Observational Study were followed through August 14, 2009. Cox proportional hazards regression models were used to estimate hazard ratios and 95% confidence intervals. Over an average 10.3 years of follow-up, 3,378 incident cases of invasive breast cancer were identified. The effect of smoking on the risk of developing invasive breast cancer was modified significantly by obesity status among postmenopausal women, regardless of whether the obesity status was defined by body mass index (P interaction = 0.01) or waist circumference (P interaction = 0.02). A significant association between smoking and breast cancer risk was noted in nonobese women (hazard ratio = 1.25, 95% confidence interval: 1.05, 1.47) but not in obese women (hazard ratio = 0.96, 95% confidence interval: 0.69, 1.34). In conclusion, this study suggests that the effect of smoking exposure on breast cancer risk was modified by obesity among postmenopausal women. The modification effect did not differ by general versus abdominal obesity.

Original languageEnglish (US)
Pages (from-to)919-928
Number of pages10
JournalAmerican Journal of Epidemiology
Issue number8
StatePublished - Oct 15 2011


  • breast neoplasms
  • obesity
  • risk factors
  • smoking

ASJC Scopus subject areas

  • Epidemiology


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