Analysis

Why studies into the link between alcohol and breast cancer have produced different results - International Scientific Forum on Alcohol Research Critique 236

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The relationship between alcohol consumption and the risk of breast cancer has been the subject of innumerable epidemiologic studies over many decades, with most showing a slight increase in risk even for light drinking. However, it has been shown that this relationship is attenuated when certain potential confounders are adjusted for, including folate levels, frequency of binge drinking and the use of post-menopausal hormonal therapy.

The ISFAR has found large differences in different studies into alcohols link with developing breast cancer

The ISFAR has found large differences in different studies into alcohol's link with developing breast cancer

A recently-released study took the results of a recent large-scale meta-analysis and sought to explain why there is a large variability of results when the 97 studies included in the analysis were compared. The authors attempted to judge to what degree differences in exposure definitions, contrast levels, different study populations, different adjustment covariates and different model approaches affected estimates of the effect of alcohol on cancer risk.

The key factor the authors used in their analyses was the ratio between the most harmful and the most protective effects of estimated risk within each study.

All of the contrasts studied - different measures of alcohol consumption, different populations, different analytic approaches and so on - had some effect on the estimates of effect of alcohol on the risk of cancer. As stated by the authors: "These findings suggest that whereas certain analytical and modelling choices, reflecting different types of alcohol and/or doses, can result in genuine differences, it is possible that many different analytical options, with different results, are pursued and selectively reported. Therefore, individual reported relative risk estimates from observational studies should be interpreted with caution."

Some ISFAR members disagreed with this conclusion, suggesting that due to marked variations in population, type of alcohol, analytic approaches, adjustment for confounding, etc, considerable error may be built in when combining data from heterogeneous studies. They felt that single large, long-term, well-done individual prospective studies may be preferable for judging the true effect of alcohol on the risk of breast cancer.

Therefore, while ISFAR reviewers appreciated the attempt to explain differences in results from previous studies to get a more valid estimate of the true relationship between alcohol consumption and the risk of breast cancer, some considered the approach described as not being a useful or valid one. Finding large differences in effects among sub-groups may not provide a reliable measure.

Alternative approaches to scrutinise findings from observational studies, including Mendelian randomisation or discussion centred on 'E-value' (which assesses how strong an unmeasured confounder would have to be to eliminate observed effect estimates), may be preferable. While such methods are imperfect, their use would be more interesting in informing the public and advancing scientific knowledge. 

To read the full critique, click here.

These critiques are published with the permission of The International Scientific Forum on Alcohol Research.

Click here for all of the critiques from the International Scientific Forum on Alcohol Research


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