Research

Age of smoking initiation and risk of breast cancer in a sample of Ontario women

Erin Young¹ , Scott Leatherdale^1,2,3 , Margaret Sloan² , Nancy Kreiger^1,2,4 and Andriana Barisic²

¹  Dalla Lana School of Public Health, University of Toronto, Toronto, Ontario, Canada

²  Department of Population Studies and Surveillance, Cancer Care Ontario, Toronto, Ontario, Canada

³  Department of Health Studies and Gerontology, University of Waterloo, Waterloo, Ontario, Canada

⁴  Department of Nutritional Sciences, University of Toronto, Toronto, Ontario, Canada

author email corresponding author email

Tobacco Induced Diseases 2009, 5:4doi:10.1186/1617-9625-5-4

Published:	17 February 2009

Abstract

Objectives

To examine the association between time of smoking initiation and both the independent and joint effects of active and passive tobacco smoke exposure and the risk of breast cancer in a sample of Ontario women.

Methods

Data from two large population-based case-control studies conducted among Ontario women aged 25–75 years were combined for analysis (n = 12,768).

Results

Women who had ever smoked and were exposed to passive smoke had a significant increased risk of breast cancer (OR 1.13, 95%CI 1.01–1.25). A significant increased risk was also observed among women who initiated smoking: at age 26 or older (OR 1.26, 95%CI 1.03–1.55); more than five years from menarche (OR 1.26, 95%CI 1.12–1.42); and, after their first live birth (OR 1.25, 95%CI 1.02–1.52).

Conclusion

The results suggest that women who initiate smoking at an older age are at an increased risk of breast cancer.