NEW YORK (Reuters Health) - Even moderate drinking may raise the risk of breast cancer among postmenopausal women on hormone replacement therapy, new research suggests.
A number of studies have linked regular drinking to a higher risk of breast cancer; it's thought that the risk reflects the effects of alcohol on women's levels of estrogen and other hormones. Similarly, hormone replacement therapy (HRT) after menopause has been shown to raise the risk of breast cancer.
The new findings, reported in the International Journal of Cancer, suggest that alcohol and HRT may combine to further boost the odds of developing the disease.
Among the more than 5,000 Danish women researchers followed, those who were on HRT and averaged one or two drinks per day had a three-fold higher risk of breast cancer than women who neither drank nor took hormones.
Women who had more than two drinks per day had a nearly five-times higher risk of the disease.
In contrast, drinking habits were not related to breast cancer risk among women who did not use HRT, according to Drs. Naja Rod Nielsen and Morten Gronbaek of the Danish National Institute of Public Health, Copenhagen.
The findings, according to the researchers, raise the possibility that drinking affects postmenopausal breast cancer risk differently depending on women's hormone use. However, more studies are needed to confirm the interaction between alcohol and hormones, they write.
The findings come from two decades' worth of data on 5,035 postmenopausal women who were surveyed about their drinking habits and hormone use at the beginning of the study. Over the next 20 years, 267 women developed breast cancer.
Overall, regular drinking was linked to a slightly higher risk of the disease. But when the researchers considered hormone use, drinking affected breast cancer risk only among women who were on HRT at the outset.
In one previous study of postmenopausal women taking oral estrogen, those who drank were found to have estrogen levels that were three times higher than those of non-drinkers, Nielsen and Gronbaek note.
This may be one explanation for the higher breast cancer risk seen in this study, they write.
If further research confirms the findings, they conclude, there should be an impact on both HRT use and recommendations for "sensible drinking limits" among postmenopausal women.
SOURCE: International Journal of Cancer, March 2008.
Research has found that both drinking alcohol and taking hormone replacement therapy (HRT) can increase breast cancer risk. The large study reviewed here combined the two by looking at how drinking alcohol while taking HRT affected breast cancer risk.
The study looked at the drinking habits and HRT use of more than 5,000 Danish women for 20 years. The researchers found:
Drinking alcohol increases estrogen levels. It's possible that the extra estrogen from drinking combined with the estrogen in HRT caused the dramatic increases in risk in this study.
When researchers look at breast cancer risk factors, they usually focus on 1 factor. This research is different because it looked at how 2 risk factors might combine to have an even larger effect on risk. According to this study, there appears to be an association between regularly drinking alcohol while taking HRT and increased breast cancer risk. And this increase in risk is higher than it would be by drinking alcohol alone or taking HRT alone.
More research needs to be done to better understand the link between drinking, taking HRT, and increased risk. In the meantime, here are some things to consider:
For more information on how to keep your breast cancer risk as low as it can be, visit the breastcancer.org Lower Your Risk section.
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