To the Editor:
I read with great interest the recent article by Liu et al
1
on the health consequences of coffee consumption. Their methodological approach was strong, and their findings were reported clearly. However, I disagree with their conclusion that on the basis of the study's findings, “it seems appropriate to suggest that younger people avoid heavy coffee consumption (ie, averaging >4 cups per day).”Liu et al reported that at baseline, the coffee drinkers in the Aerobics Center Longitudinal Study cohort, like many other populations, were more likely to smoke cigarettes. The authors did an excellent job in handling this well-recognized association. Their multivariate models (2 and 3) were adjusted for smoking. The authors recognized that residual confounding from smoking could still exist and that this could lead to the appearance of a mortality risk from coffee. Indeed, this was mentioned in their “Limitations” section. To eliminate possible residual confounding, the authors stratified their analysis by smoking status and presented their findings separate from the article as supplemental online material. The authors reported that “we did not observe the significant association between coffee consumption and all-cause mortality both in current smokers and non-current smokers.”
The supplemental figures actually show what appears to be an inverse relationship for male nonsmokers between coffee consumption and all-cause mortality for consumption of 8 to 14 through 22 to 28 cups per week, with a hazard ratio below 1 for the latter category. Female nonsmokers in all coffee consumption categories appear to have hazard ratios that approximate the null value without the appearance of increased risk with increased coffee consumption even in the highest consumption category (>28 cups per week).
Although moderation in all things has historically been good advice, the recommendation for younger people to cut back on their coffee consumption does not appear to be well supported by the data presented.
Reference
- Association of coffee consumption with all-cause and cardiovascular disease mortality.Mayo Clin Proc. 2013; 88: 1066-1074
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© 2013 Mayo Foundation for Medical Education and Research. Published by Elsevier Inc. All rights reserved.
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- Association of Coffee Consumption With All-Cause and Cardiovascular Disease MortalityMayo Clinic ProceedingsVol. 88Issue 10
- In Reply—Association of Coffee Consumption With All-Cause and Cardiovascular Disease MortalityMayo Clinic ProceedingsVol. 88Issue 12
- PreviewWe thank Drs Katz, Wagner, Card, and Greitzer et al for their interest in our article on coffee consumption and mortality.1 Due to the observational nature of our study design, the association of coffee consumption with all-cause mortality or disease-specific mortality could not be verified as representing causality because of unmeasured or unknown potential confounding factors or alternative explanations. We agree with Wagner et al that the confounding effect from smoking could potentially play an important role in this association.
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