Can Too Much Coffee Kill?

A new look into the numbers suggests that some heavy coffee drinkers are more than twice as likely to die as their peers. Should you be worried?

Can too much coffee kill?     Photo: Teo Tarras/Shutterstock

"Lean and fit people did not appear to be at increased risk."

Coffee and health are back in the news with a new study in Mayo Clinic Proceedings showing that heavy coffee drinking (28 cups per week) increased the risk of all-cause mortality in people less than 55 by about 50 percent in men and two fold in women.

This study is the most recent of a long line of frequently conflicting research in various populations showing that coffee is good, bad or “it depends."

It included more than 40,000 people who were followed for 17 years on average. Careful statistical analysis was done and factors like smoking, physical activity, and other health behaviors and risk factors were controlled for. 

One of the key findings was that at least for men having a BMI greater than 25 was associated with the biggest increase in risk. Lean and fit people did not appear to be at increased risk.  

Strangely, for people older than 55, heavy coffee consumption had no effect on the mortality statistics. The authors also pointed out that even though this is a huge study, some of stats they wanted to run on subgroups of participants did not have enough people to permit the comparisons to be made. So sometimes big data is not big enough!

What Other Data Say
This new report contrasts with a recent meta-analysis of a large number of studies on coffee and health.  According to the analysis, coffee consumption is mildly protective and it does not increase your risk for cardiovascular disease, stroke, or cancers. Another recent study, this time from Harvard, that has followed thousands of women for many years, shows no increased risk for breast cancer from caffeinated beverages. The same study shows that coffee might in fact be protective against diabetes. Surprisingly, it shows an anti-diabetic effect for both regular and decaf coffee, suggesting that the drink’s benefits don’t come from caffeine alone.

Why You Can Relax
The main thing to remember when you read about coffee or caffeine and health is that if you look hard enough, you can find individual studies that report all sorts of good and bad things.  The key is to look at all the evidence in a comprehensive way—easy advice to give, but hard to follow for the average person surrounded on all sides by the media circus we all live in. But when you take the balanced approach, coffee seems to be pretty good for you in most situations.

What About Exercise?
Caffeine is perhaps the most frequently used ergogenic aid around, and it works—though nobody knows exactly how.  For a long time the idea was that caffeine mobilized fat from fat cells and increased the use of fat by the muscles during exercise. The idea went that people could move at the same pace while using less glycogen, reducing the chance of hitting the wall and leading to improved performance.

However, on further review that idea seems to have fallen by the wayside and the focus now is on caffeine as a psycho stimulant. In other words, caffeine does things to the brain to make us more alert, changing how we perceive effort and fatigue.

The military has been interested in caffeine as a psycho stimulant for use in people who are sleep deprived or perhaps in pilots flying long missions. When used in these situations it can be nearly as effective as more powerful stimulants, including amphetamines!  A scientific review of caffeine on cognitive performance concludes what a lot of people who have crammed for tests already know:

“Caffeine improves performance on simple and complex attention tasks, and affects the alerting, and executive control networks...Evidence shows that caffeine has clear beneficial effects on attention, and that the effects are even more widespread than previously assumed.”

Coffee Addiction
The psychiatrists have gotten into the act and concluded that at least some people can get addicted to coffee (is this a surprise?). There is also the issue of caffeine withdrawal, which can include all sorts of symptoms related to increased fatigue, lack of feeling sharp, headache, and even nausea.   

(There are a number of protocols out there about how to withdraw from caffeine in general and coffee in specific, but the key appears to be a slow taper over time. One guidline: Reduce your consumption 25-30 percent per week over a few weeks or a month.)  

Back to the Brain
When I took a quick look at the medical literature on this topic one summary paper that hit me concluded that:

“The consumption of moderate amounts of caffeine 1) increases energy availability, 2) increases daily energy expenditure, 3) decreases fatigue, 4) decreases the sense of effort associated with physical activity, 5) enhances physical performance, 6) enhances motor performance, 7) enhances cognitive performance, 8) increases alertness, wakefulness, and feelings of 'energy,' 9) decreases mental fatigue, 10) quickens reactions, 11) increases the accuracy of reactions, 12) increases the ability to concentrate and focus attention, 13) enhances short-term memory, 14) increases the ability to solve problems requiring reasoning, 15) increases the ability to make correct decisions, 16) enhances cognitive functioning capabilities and neuromuscular coordination, and 17) in otherwise healthy non-pregnant adults is safe.”

The fact that there were 17 concluding points to the article made me wonder just how much coffee the authors had consumed when they were writing it! 

Overall, it seems that even 28 cups of coffee per week is safe in terms of your general health and may, in fact, be protective against a number of conditions. Higher levels of consumption are probably fine in most otherwise fit people. 

Michael J. Joyner, M.D., is a physiologist and anesthesiologist at the Mayo Clinic and a leading voice in the world of exercise physiology. Over the last 25+ years, he's published 100s of studies many of which have focused on how humans respond to exercise. Dr. Joyner also writes at Human Limits. The views expressed in this post are his own and do not reflect those of his employer.

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