Tuesday April 9 2013
Moderate alcohol consumption may improve survival rates
“A glass of wine a day will not affect a woman’s chance of beating breast cancer,” reports the Mail Online website.
It has long been known that higher alcohol intake is associated with increased risk of developing breast cancer. It is less clear whether the amount a woman drinks before or after a breast cancer diagnosis has any effect on her chances of survival.
The news is based on a new study that found that moderate alcohol consumption before breast cancer diagnosis is associated with a reduced risk of death due to breast cancer compared to never drinking. Similarly, alcohol intake after a breast cancer diagnosis was not associated with increased risk of death from breast cancer.
These findings suggest that although drinking alcohol increases your risk of getting breast cancer, it might not increase your risk of actually dying from breast cancer. For this reason, it’s best to stick with the NHS guidelines on alcohol consumption.
The researchers also found that moderate consumption of alcohol before diagnosis (one to nine drinks per week) was associated with a reduced risk of dying from heart disease and with reduced risk of death from any cause compared to never drinking at all. Women who consumed higher levels of alcohol after diagnosis were also less likely to die from cardiovascular disease or from any cause than women who never drank.
The findings do not change current alcohol recommendations – women should not drink more than two to three units a day.
Where did the story come from?
The study was carried out by researchers from the Fred Hutchinson Cancer Research Centre and the Harvard Medical School and Brigham and Women’s Hospital in the US in collaboration with an international team of researchers. It was funded by the US National Cancer Institute and the charity Komen for the Cure.
The study was published in the peer-reviewed Journal of Clinical Oncology.
This story was covered by the Mail Online website. The Mail concentrated on the link between wine intake and the reduction in risk of dying from heart disease (drinking beer and spirits did not have the same effect). The study did reach this conclusion (prior to diagnosis), but as it was based on a limited sample size the researchers did not attach the same level of significance to the findings as the Mail chose to.
The main focus of the study was the effect of alcohol on breast cancer deaths.
What kind of research was this?
This was a cohort study that aimed to analyse the relationship between alcohol consumption and breast cancer survival.
This is the ideal study design. However, like all cohort studies it can only show associations between alcohol consumption and changes in risk, and not direct cause and effect. This is because there may be other factors responsible for the association seen (confounders).
What did the research involve?
The researchers recruited to their study 22,890 women aged between 20 and 79 years old who were diagnosed with breast cancer between 1985 and 2006.
The women were asked to report their alcohol consumption prior to their diagnosis, and a sub-sample also reported on their drinking habits after their diagnosis (4,881 women, alcohol consumption reported on average 5.7 years after diagnosis) via telephone interview.
Separate questions were asked on the amount and frequency of beer, wine and spirits intake. Alcohol intake was classified as:
- never drinking
- one to two drinks per week
- three to six drinks per week
- seven to nine drinks per week
- 10 or more drinks per week
Women were also asked about other breast cancer risk factors, including:
- reproductive and menstrual history
- physical activity
- family history of cancer
- use of oral contraceptives
- hormone replacement therapy
Information about their breast cancer was also collected (such as the stage that the disease had progressed to).
The women were followed up for a median of 11.3 years after their diagnosis. Deaths during follow-up were monitored using the National Death Index.
The researchers looked at the association between alcohol consumption and death from breast cancer, cardiovascular disease (diseases that affect the heart and blood vessels, such as heart disease) or from any cause, after adjusting for a number of potential factors that could explain any association seen (confounders).
What were the basic results?
During the 11.3 years of follow-up 7,780 deaths occurred, 3,484 of which were due to breast cancer. The researchers found that moderate alcohol consumption before diagnosis was associated with breast cancer survival.
Compared to non-drinkers, women who consumed three to six drinks per week had a significantly reduced risk of dying from breast cancer (hazard ratio (HR) 0.85, 95% confidence interval (CI) 0.75 to 0.95).
The results were not statistically significant for other levels of alcohol intakes – one or two drinks, or more than six.
Women who drank spirits one or twice per week (compared to never drinking spirits) had a borderline significant reduced risk of death from breast cancer (HR 0.92, 95% CI 0.85 to 1.00), but in general results did not vary much by type of alcohol (beer, wine or spirits) consumed.
Consuming between one and nine drinks per week was associated with a reduced risk of death from cardiovascular disease, and of death from any cause, compared to never drinking.
Looking at a sub-cohort of women who provided information about alcohol consumption after their breast cancer diagnosis (4,881 women), alcohol consumption at any level after diagnosis was not significantly associated with a reduced risk of death from breast cancer (after adjusting for how much they drank before their diagnosis). No type of alcohol was associated with any change in risk. However, women who consumed high levels of alcohol after diagnosis (10 or more drinks per week) were less likely to die from cardiovascular disease, and women who drank more than three drinks per week were less likely to die from any cause.
The researchers also looked to see if changing alcohol intake after diagnosis was associated with death from breast cancer, cardiovascular disease or any cause.
Increasing or decreasing alcohol intake was not associated with an increased risk of death from breast cancer.
However, women who increased alcohol consumption by more than one drink per week after diagnosis were at decreased risk of death from cardiovascular disease or death from any cause.
How did the researchers interpret the results?
The researchers conclude that, “overall alcohol consumption before diagnosis was not associated with disease-specific survival, but we found a suggestion favouring moderate consumption. There was no evidence for an association with post-diagnosis alcohol intake and breast cancer survival. This study, however, does provide support for a benefit of limited alcohol intake for cardiovascular and overall survival in women with breast cancer”.
The researchers also state that, “although women may alter their habits after breast cancer diagnosis, our results do not support a meaningful effect of changing consumption patterns on breast cancer survival”.
This large cohort study with a long follow-up has found that moderate alcohol consumption before breast cancer diagnosis (three to six drinks per week) is associated with a reduced risk of death due to breast cancer, but that alcohol intake after diagnosis did not have any benefit, but also did not cause any harm.
The study also found that consuming between one and nine drinks per week before a diagnosis of breast cancer is associated with a reduced risk of death from cardiovascular disease, and of death from any cause, compared to never drinking.
The study also suggested that women who consumed higher levels of alcohol after diagnosis (10 or more drinks per week) were less likely to die from cardiovascular disease. However, this group of women represented a much smaller sample, so these risk figures are less reliable.
Women who drank more than three drinks per week after diagnosis were less likely to die from any cause than women who never drank.
Women who increased their level of alcohol consumption after breast cancer diagnosis had better survival from cardiovascular disease and other causes, and did not affect their survival from breast cancer.
This research has the strengths of being a large cohort study with long-follow-up and it collected information on and adjusted for a number of potential confounding factors. However, it suffers from the inherent limitation of all cohort studies in that it can only show association and not cause and effect due to the possibility of confounding factors.
In addition, alcohol consumption was based on self-reported values for the previous two years, and may be subject to recall bias as well as possibly not being representative of alcohol consumption during the women’s lifetime.
Also, post-diagnosis alcohol consumption was collected on average 5.7 years after diagnosis, meaning that the results for post-diagnosis alcohol intake may only be applicable to women who survive several years after diagnosis.
Overall, this study suggests that moderate alcohol consumption prior to breast cancer diagnosis may be associated with improved breast cancer survival, but it found no link between any level of alcohol consumption after cancer diagnosis and breast cancer survival.
However, the study also suggests that alcohol intake is associated with improved cardiovascular and overall survival.
Taking into account the other health risks associated with alcohol consumption, this study would suggest that women living with or recovering from breast cancer should not worry about the occasional drink. But like all women, they should not regularly exceed the recommended consumption levels for women (two to three units a day, or 14-21 units per week).
Analysis by NHS Choices. Follow Behind the Headlines on Twitter.