The authors state that the association between alcohol consumption and breast cancer has been largely investigated, but few studies have investigated the effects of average intake when the pattern of drinking is taken into account. They sought to examine the association between drinking pattern of alcoholic beverages, particularly wine, and breast cancer using different statistical approaches. Their study included 437 cases of breast cancer, newly diagnosed in the period 20022004, and 922 residence- and age-matched controls.
Results showed that women who had an average consumption of total alcohol of less than 1.5 drinks per day had a lower risk (odds ratio [OR] = 0.58, 95% confidence interval [CI] = 0.340.97) when compared with nondrinkers. This protective effect was due substantially to wine consumption since the proportion of regular wine drinkers is predominant in their study population. Furthermore, women who consumed between 10 and 12 g/d of wine had a lower risk (OR = 0.51; 95% CI = 0.300.91) when compared with nonwine drinkers. Above 12 g per day of wine consumption, the risk of breast cancer increased, but the association was nonsignificant.
The authors conclude that although no association between the pattern of total alcohol consumption and breast cancer was found, the type of alcoholic beverage seemed to play an important role in this association. Their results support the hypothesis that there is a threshold effect that risk decreased or was not modified for consumption under a certain threshold. Above that threshold, risk increased, however. The drinking pattern of each type of specific beverage, especially wine, seems important in terms of alcoholbreast cancer association. Low and regular wine consumption does not increase breast cancer risk.
R Curtis Ellison comments: Most of the initial studies showing an association between alcohol drinking and breast cancer were based on the amount of alcohol consumed by women. The present study had data on the pattern of drinking, and was also able to adjust for some of the known risk factors for breast cancer (e.g., breast cancer in a mother or sister, education, increased number of ovulatory cycles, physical activity, obesity).
We have some questions about the analysis. Most investigators use quadratic or cubic spline regression models to depict the dose-reponse relationship instead of free knot splines; we are not sure that the spline analyses as carried out add much to the paper, as similar results were seen when conventional categories of drinking were used to estimate breast cancer risk. Further, in the present study, some risk factors (e.g., age at menarche, age at menopause, oral contraceptive use, hormone replacement therapy) were not included in the final regression model because they did not show a certain level of significance in univariate analyses; we prefer that such potentially important factors be retained in final models.
In any case, the analyses found that, in comparison with lifetime abstainers, there was no increase but a significant reduction of about 40% in the risk of breast cancer for women who consumed between 1 and 1.5 drinks/day. For wine consumption, there was an even a greater lowering of risk for women consuming approximately one typical drink/day. There was a trend towards an increase in breast cancer risk for women consuming more alcohol or wine, but there were too few heavy drinkers in the study to obtain good estimates of effect at such levels of drinking.
One of the key messages of this paper, which must be confirmed by others, is that there appears to be a threshold for alcohol leading to an increase in risk of breast cancer. The estimate from this paper is that this threshold is about 1.5 to 2 drinks/day. Frequent (6 or 7 days/week) drinking of any type of beverage did not show an increase in breast cancer risk. If similar results are found in other studies, they provide further reassurance to women who follow the USDA guidelines of no more than one drink/day of 14g.
Source: Bessaoud F, Daurés JP. Patterns of alcohol (especially wine) consumption and breast cancer risk: A case-control study among a population in southern France. Ann Epidemiol 2008;pre-publication internet release, 5/5/08.