This large study from Denmark was designed to test the hypothesis that 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 (CHD) compared with women who exhibit a stable alcohol intake. It consisted of more than 20.000 postmenopausal women who had two assessments of alcohol intake, about 5 years apart; changes during that period were related to their subsequent risk of developing breast cancer or CHD, or dying, during the subsequent follow-up period that averaged 8 years.
For the risk of breast cancer, the baseline alcohol consumption reported by the women showed that higher alcohol intake was associated with a greater risk of developing breast cancer during follow up, but a lower risk of developing CHD and for total mortality. For relating changes in alcohol intake in the 5 years between the two alcohol assessments, those who increased their reported alcohol intake showed an increased risk of subsequent breast cancer, while those who decreased their intake also had a tendency for greater breast cancer. In terms of CHD and total mortality, the data were consistent with an increase in consumption lowering risk, while there was a tendency for a decrease in consumption to increase risk. Hence, the directionality for risk from changes in intake reflected the risks associated with baseline risk, and the authors conclude that their results “ . . .support the hypotheses that alcohol intake is associated with increased risk of breast cancer and decreased risk of coronary heart disease.”
Forum reviewers considered this to be a very well-done study. They, and the authors, appreciated the innate difficulty in separating effects on health of usual alcohol intake over time and changes over a limited period of time. Reviewers were also concerned by these problems, suggesting that some of the reported changes in alcohol consumption in this study may have just reflected individuals replying differently to questions regarding their drinking at different points of time. Further, the reason why some women may have actually increased or decreased their intake are not known.
Nevertheless, Forum members applaud the attempt of the authors to judge if changes in alcohol intake relate to cancer, CHD, and total mortality. This is a difficult task given that baseline and life-time alcohol consumption clearly relate to these outcomes. Further, data on the pattern of drinking (regular versus binge), any estimate of underreporting of alcohol, the type of beverage consumed and, as stated by the authors, certain known risk factors of breast cancer, were not available to be included in their analyses. Thus while the results of this study add important information on the relation of alcohol to disease, there remain questions about the specific relevance of changes in intake for such outcomes.
Reference: Dam MK, Hvidtfeldt UA, Tjønneland A, Overvad K, Grønbæk M, Tolstrup JS. Five year change in alcohol intake and risk of breast cancer and coronary heart disease among postmenopausal women: prospective cohort study. BMJ 2016;353:i2314. http://dx.doi.org/10.1136/bmj.i2314