Five year change in alcohol intake and risk of breast cancer and coronary heart disease among postmenopausal women: prospective cohort study

Abstract

Objective: To test the hypothesis that postmenopausal women who increase their alcohol intake over a five year period have a higher risk of breast cancer and a lower risk of coronary heart disease compared with stable alcohol intake.

Design: Prospective cohort study.

Setting: Denmark, 1993-2012.

Participants: 21 523 postmenopausal women who participated in the Diet, Cancer, and Health Study in two consecutive examinations in 1993-98 and 1999-2003. Information on alcohol intake was obtained from questionnaires completed by participants.

Main outcome measures: Incidence of breast cancer, coronary heart disease, and all cause mortality during 11 years of follow-up. Information was obtained from the Danish Cancer Register, Danish Hospital Discharge Register, Danish Register of Causes of Death, and National Central Person Register. We estimated hazard ratios according to five year change in alcohol intake using Cox proportional hazards models.

Results: During the study, 1054, 1750, and 2080 cases of breast cancer, coronary heart disease, and mortality occurred, respectively. Analyses modelling five year change in alcohol intake with cubic splines showed that women who increased their alcohol intake over the five year period had a higher risk of breast cancer and a lower risk of coronary heart disease than women with a stable alcohol intake. For instance, women who increased their alcohol intake by seven or 14 drinks per week (corresponding to one or two drinks more per day) had hazard ratios of breast cancer of 1.13 (95% confidence interval 1.03 to 1.23) and 1.29 (1.07 to 1.55), respectively, compared to women with stable intake, and adjusted for age, education, body mass index, smoking, Mediterranean diet score, parity, number of births, and hormone replacement therapy. For coronary heart disease, corresponding hazard ratios were 0.89 (0.81 to 0.97) and 0.78 (0.64 to 0.95), respectively, adjusted for age, education, body mass index, Mediterranean diet score, smoking, physical activity, hypertension, elevated cholesterol, and diabetes. Results among women who reduced their alcohol intake over the five year period were not significantly associated with risk of breast cancer or coronary heart disease. Analyses of all cause mortality showed that women who increased their alcohol intake from a high intake (≥14 drinks per week) to an even higher intake had a higher mortality risk that women with a stable high intake.

Conclusion: In this study of postmenopausal women over a five year period, results support the hypotheses that alcohol intake is associated with increased risk of breast cancer and decreased risk of coronary heart disease.

Fig 1 Hazard ratios of breast cancer among postmenopausal women by five year change in alcohol intake. Blue solid curve (black dashed lines)=hazard ratios (95% confidence intervals) of breast cancer by change in alcohol intake from the 1993-98 to the 1999-2003 examinations, modelled by cubic splines; stepped line=hazard ratios of breast cancer for seven categories of change in alcohol intake. Women who changed their alcohol intake outside the 0.5-99.5% percentiles of the distribution of change in alcohol intake were excluded from analyses presented in the figure, resulting in 20  890 women and 1045 cases of breast cancer eligible for analysis. Estimates are adjusted for age, education, body mass index, smoking, Mediterranean diet score, parity, number of births, hormone replacement therapy, and alcohol intake in the 1993-98 examination

Fig 2 Hazard ratios of coronary heart disease among postmenopausal women by five year change in alcohol intake. Blue solid curve (black dashed lines)=hazard ratios (95% confidence intervals) of coronary heart disease by change in alcohol intake from the 1993-98 to the 1999-2003 examinations, modelled by cubic splines; stepped line=hazard ratios of coronary heart disease for seven categories of change in alcohol intake. Women who changed their alcohol intake outside the 0.5-99.5% percentiles of the distribution of change in alcohol intake were excluded from analyses presented in the figure, resulting in 20 433 women and 1730 cases of coronary heart disease eligible for analysis. Estimates are adjusted for age, education, body mass index, Mediterranean diet score, smoking, physical activity, hypertension, elevated cholesterol, diabetes, and alcohol intake in the 1993-98 examination