Fluke or Trend? Coffee Consumption and Longevity

Alvin B. Lin, MD, FAAFP
 
Dr. Lin is an associate professor of family and community medicine at University of Nevada School of Medicine and an adjunct professor of family medicine and geriatrics at Touro University Nevada College of Medicine. He also serves as an advisory medical director for Infinity Hospice Care and as medical director of Lions HealthFirst Foundation. Dr. Lin maintains a small private practice in Las Vegas, NV. The posts represent the views of Dr. Lin, and in no way are to be construed as representative of the above listed organizations. Dr. Lin blogs about current medical literature and news at http://alvinblin.blogspot.com/.

As you might have guessed, I read USA Today quite a bit, so of course, I stumbled on their report about a possible link between coffee consumption and mortality in which the reporter pitted a Harvard professor of public health against the chief of cardiology at the Cleveland Clinic. While neither were involved in the study, the former found the findings intriguing while the latter picked apart the study and thus concluded the findings were nonsensical. The lead author agreed that the study design did not prove that coffee affects mortality and thus could not be used as evidence to go out and start drinking coffee. So will coffee really affect our longevity?

It turns out that a prospective cohort study published in the Annals of Internal Medicine addressed this same issue back in June 2008 when the authors followed 41,736 men in the Health Professional Follow-Up Study for 18 years and 86,214 women in the Nurses' Health Study for 24 years, all without any history of heart disease and/or cancer at baseline. To their credit, the authors assessed coffee consumption every 2 to 4 years. While some participants rarely drank any coffee, there were some who drank 6 or more cups/day! The good news back then was the coffee consumption was not associated with all-cause mortality in either men or women. In fact, there was a hint of decrease risk in women.

Fast forward 4 years to the New England Journal of Medicine which published today the results of the prospective cohort analysis of 229,119 male and 173, 141 female participants in the National Institutes of Health - AARP Diet & Health Study who were 50 to 71 years old (average age, 61 years) at baseline and free of cancer, heart disease and stroke. After 14 years of follow-up, the authors actually found that greater coffee consumption was associated with lower all-cause mortality, after taking into account the usual confounders.

But as expected, association does not prove causation. What's worse, the authors only checked for coffee consumption just once at the beginning of the study. So as cardiologist Dr. Steve Nissen pointed out, habits vary over time. It makes no sense to base a long-term association upon just one assessment. However, I have to agree with Dr. Frank Hu that it makes sense to take into account the usual suspects, eg subtract out as many confounding factors as possible, including tobacco use. After all, we do this for all other studies.

So the debate rages on. The good news for those who love their morning cuppa joe is that we have two large, long-term studies, neither of which demonstrate any harm with greater consumption. Since this looks more like a trend than a fluke, go out and enjoy your morning brew.