Live Long and Drink Coffee
Does coffee help you live longer? Neal Freedman at the National Cancer Institute’s Division of Cancer Epidemiology and Genetics and his colleagues consider this question in a recent study published in the New England Journal of Medicine. Freedman talks more about the association of coffee drinking with mortality in an interview published in the February 19 issue of the Journal of Caffeine Research.
Freedman and his colleagues analyzed data from surveys of roughly 400,000 AARP members, collected over roughly a dozen years. The AARP members’ ages ranged from 50 to 71 when the study began in 1995-96.
When the researchers looked at coffee drinking and mortality for the entire group, they found a positive correlation between coffee drinking and death. At first gulp, this made it seem as if coffee drinking could cut short your time to live long and prosper.
However, the AARP study group also showed a strong correlation between coffee drinking and cigarette smoking. Freedman and friends analyzed the data again, this time controlling for cigarette smoking and several other unhealthy behaviors. Now the data showed a slight inverse relationship between coffee drinking and death. In other words, coffee drinkers who didn’t smoke were more likely to live longer.
So, what does the study mean? For one thing, I’m going to keep enjoying my coffee. After all, I do call this blog Summa Cum Latte. Perhaps more importantly, the study spotlights basic principles of statistics.
First, correlation does not necessarily mean there is a causation. The increased risk of death that the researchers first saw resulted mainly from the fact that cigarette smokers tend to drink coffee. Cigarette smoking does kill people. More than 1,200 Americans die every day from tobacco-related causes. Yup, that’s 1,200 per day!
Second, every statistical study has limits. The study showed that nonsmoking coffee drinkers had a 10-15% lower chance of dying. However, it did not say why that correlation existed. Nor did it say whether caffeine or another chemical in coffee might explain that result.
The survey questions didn’t distinguish between people who only drink decaf and those who only drink hi-test. The study likewise didn’t draw distinctions between different types of coffee preparations. These may be questions for further study, says Freedman.
This brings up a third point: Good scientific studies don’t just answer questions. They often raise issues for further investigation. Learning one thing should make us want to explore more. After all, science is a quest for discovery.
And now it’s time for more coffee.