You may recently have read in the media reports suggesting that drinking a small amount of alcohol is linked to a slight increase in the risk of breast cancer?
News reports followed publication of a study conducted by researchers at Harvard University and Brigham and Women's Hospital in Boston, which explored the association between low-level alcohol consumption (traditionally publicised as having a protective effect on health, particularly the heart) and lifetime drinking patterns on breast cancer. Previous studies have associated high alcohol consumption with an increased risk, but this study aimed to identify what risks there were, if any, to women consuming low levels of alcohol.
The researchers used data collected from 105,986 women enrolled in the Nurses' Health Study. Average alcohol consumption was assessed over the previous year in 1980, then again seven times until 2008. These data were combined to estimate average alcohol intake over this period. A cohort study like this (and our own study - DietCompLyf) looks at the effects of diet and lifestyle on health outcomes in a large group of people over a long period of time. Researchers always try to control for any features which may influence the associations being studied to ensure results are trustworthy, however they cannot prove cause and effect.
The exact mechanism for the reported link is unknown, but it may be due to alcohol's effects on oestrogen levels. Alcohol reduces the liver's ability to remove oestrogen from the body, therefore leading to rises in the body's oestrogen levels, stimulating a rapid increase of mammary cells, which raises the risk of breast cancer. Other mechanisms include the production of compounds formed through the breakdown of alcohol in the liver, which are known to cause cancer mutations in cells which usually protect and repair DNA.
This was a very large study from a much respected source; however interpretation of the included results must be made with caution. Asking participants to complete a questionnaire reporting their alcohol consumption from the previous year is not easy. People can misreport their alcohol use dependent on when they completed their questionnaires and whether they are reporting actual intakes or what they think they should report.
The sample demographic, which in this case was predominately white, exposed to shift work (a known risk factor for breast cancer), and other factors which are potentially associated with both alcohol intake and risk of breast cancer (such as use of hormone therapy, family history of breast cancer, age at first period and menopause) may also influence results, if sufficient information was not collected to enable full control (the authors do note an attempt at this). Despite this, the link between breast cancer and alcohol is not a new one, and the findings back up the results of several previous studies.
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