Heavy Coffee Consumption Linked With Increased Risk of All-Cause Death
Michael O'Riordan
Drinking more than four cups of coffee per day does more than increase the risk of the jitters, a new study suggests[1]. Researchers report that heavy coffee consumption, defined as more than 28 cups of coffee per week, is associated with an increased risk of all-cause mortality among men.
For men and women 55 years of age and younger, the association between heavy coffee consumption and all-cause mortality is more pronounced.
"Typically, people have been concerned that coffee could be unhealthy, particularly caffeine," Dr Chip Lavie (Ochsner Medical Center, New Orleans, LA), one of the study authors, told heartwire . "If you give a massive acute dose of caffeine, you raise your pulse and blood pressure, and that can be toxic. So years ago, people had the thought that maybe coffee could be a bad or unhealthy thing to be drinking."
Previous studies had suggested an association between heavy coffee consumption and all-cause mortality and coronary heart disease, but many of these older studies are compromised, because heavy coffee drinkers were also smokers, two habits that went hand in hand. When adjusted for smoking, the coffee didn't appear to be very toxic, said Lavie, and most of the later studies suggested that coffee consumption wasn't harmful.
In fact, said Lavie, there are some potential benefits of coffee, although these data are not particularly strong. As reported previously by heartwire , there are studies suggesting coffee might protect against heart failure, diabetes, stroke, and other conditions.
A Cup Is 8 oz, Not 20!
In this latest study, which is published online August 15, 2013 in the Mayo Clinic Proceedings, lead investigator Dr Junxiu Liu (University of South Carolina, Columbia) and colleagues assessed the data from the Aerobics Center Longitudinal Study. The retrospective analysis included 43 727 participants followed for a median of 17 years, during which time 2512 deaths occurred. Of these deaths, 32% were the result of cardiovascular disease.
Despite the limitations of the study, Lavie told heartwire , "it certainly looks like people who report intakes of low amounts of coffee are not getting significant harm, and that's up to about 28 cups a week, which is a decent amount of coffee." He pointed out that a cup of coffee as measured is an 8-oz cup, and not the supersized 20-ounce cups typical of Starbucks and other coffee chains.
In a multivariate analysis, men who drank more than 28 cups of coffee had a statistically significant 21% increased risk of all-cause mortality. In women, the risk was not statistically significant. In men younger than 55 years of age, drinking more than 28 cups per week was associated with a 56% increased risk of death compared with nondrinkers. In younger women, such heavy consumption increased the risk of death 113% compared with those who did not drink coffee.
Overall, there was no association between coffee consumption and cardiovascular mortality.
"Explaining why, we can try to tease stuff out, but I don't really have a good reason to explain why noncardiovascular mortality is increased," said Lavie. "And noncardiovascular mortality includes a lot of different things--it includes cancer and mortality from suicides and accidents and infections. Why would a high amount of coffee increase noncardiovascular mortality, particularly in young people? The mechanism is not clear. It might be only an association. It may not be that coffee caused the death. This is the case with studies that aren't randomized, and we're never going to get a randomized study of something like coffee."
Still, Lavie said, there are strengths to the analysis, including the long-term follow-up, the number of participants, and the fact they were able to adjust for cardiorespiratory fitness. For people who like coffee, including himself, Lavie said the study suggests coffee is relatively safe if people limit themselves to less than four cups of coffee per day. For those who consume more, Lavie said the research is not intended to scare anyone, but it can't hurt for people to think about the association.
"Honestly, for myself, I could easily go some days having a sixth cup of coffee, but this is leading me now to try to limit myself to the third, and maybe occasionally have the fourth," said Lavie. "Most days now I'm sticking with two or three cups. And honestly, for most people, it's a habit. There's something to the first or second cup, but if you're drinking it all day long it's really just a habit. And if you have a signal for increased mortality, and you know about that, it might make people think or stop after the third cup."
