Smoking duration before first childbirth: an emerging risk factor for breast cancer? Results from 302,865 Norwegian women
Open Access
- 1 May 2013
- journal article
- research article
- Published by Springer Science and Business Media LLC in Cancer Causes & Control
- Vol. 24 (7), 1347-1356
- https://doi.org/10.1007/s10552-013-0213-1
Abstract
Purpose Recently, The International Agency for Research on Cancer classified cigarette smoking as possibly carcinogenic to the human breast. Since some new cohort studies have suggested that this risk is confined to women who started to smoke before first childbirth, we wanted to examine the association between smoking and breast cancer, with a focus on time of smoking initiation in relation to the first childbirth. Methods We followed 302,865 Norwegian women born between 1899 and 1975, recruited from 1974 to 2003, by linkage to national registries through December 2007. We used Cox proportional hazard models to estimate hazard ratios (HR) and 95 % confidence intervals (CI). Results During more than 4.1 million person-years of follow-up, we ascertained 7,490 cases of primary invasive breast cancer. Compared with never smokers, ever smokers had a 15 % (HR = 1.15, 95 % CI 1.10–1.21) increased risk of breast cancer overall and also a significantly increased risk of breast cancer in the three most exposed categories of age at smoking initiation (parous women), number of cigarettes smoked per day, years of smoking duration and number of pack-years. Ever smokers who started to smoke more than 1 year after the first childbirth had not an increased risk (HR = 0.93, 95 % CI 0.86–1.02), while those who initiated smoking more than 10 years before their first childbirth had a 60 % (HR = 1.60, 95 % CI 1.42–1.80) increased risk of breast cancer, compared with never smokers. Conclusion Smoking initiation before the first childbirth increases the risk of breast cancer.Keywords
This publication has 28 references indexed in Scilit:
- The Increased Risk of Colon Cancer Due to Cigarette Smoking May Be Greater in Women than MenCancer Epidemiology, Biomarkers & Prevention, 2013
- Smoking Before the First Pregnancy and the Risk of Breast Cancer: A Meta-AnalysisAmerican Journal of Epidemiology, 2011
- Cigarette Smoking and the Incidence of Breast CancerArchives of Internal Medicine, 2011
- Active smoking and secondhand smoke increase breast cancer risk: the report of the Canadian Expert Panel on Tobacco Smoke and Breast Cancer Risk (2009)Tobacco Control, 2010
- Estimates of worldwide burden of cancer in 2008: GLOBOCAN 2008International Journal of Cancer, 2010
- Cohort Profile: The Metabolic syndrome and Cancer project (Me-Can)International Journal of Epidemiology, 2009
- Cohort Profile: Cohort of Norway (CONOR)International Journal of Epidemiology, 2007
- Smoking Cigarettes before First Childbirth and Risk of Breast CancerAmerican Journal of Epidemiology, 2007
- Active and Passive Smoking in Breast CancerEpidemiology, 2002
- Differentiation of the mammary gland and susceptibility to carcinogenesisBreast Cancer Research and Treatment, 1982