Coffee drinkers live longer, according to two large-scale studies that add to extensive research indicating coffee consumption is associated with better health.
The studies examined the health histories of hundreds of thousands of people who were tracked over many years. They found that coffee-drinking reduced the risk of various diseases among people from several ethnicities, and this effect was seen in drinkers of regular or decaffeinated coffee. And the more coffee consumed, the greater the benefit.
These are observational studies, not controlled clinical trials. So while they demonstrate an association, they don't prove cause and effect. But at the least, researchers said the latest evidence reinforces a large body of previous reports indicating there's no harm from coffee – and that it might very well benefit people's health.
Both of the new studies were published in the Annals of Internal Medicine. They asked participants about whether they drank coffee, and if so, how much. Participants were also asked about habits that influence health, such as smoking, exercise and heart disease.
One study was led by Veronica W. Setiawan of the University of Southern California. Funded by the National Cancer Institute, it examined coffee-drinking habits among more than 180,000 people. They were followed for an average of 16 years.
The other was performed by European scientists from Imperial College London and the International Agency for Research on Cancer, led by Marc J. Gunter of the IARC. It examined coffee-drinking among more than 520,000 adults from 10 European countries.
The study led by Setiawan found those drinking one cup of coffee daily had a 12 per cent lower risk of death from heart disease, cancer, stroke, diabetes, respiratory and kidney disease. For those drinking three cups a day, the risk reduction rose to 18 per cent.
In previous studies, the great majority of those examined were white, meaning that environmental and lifestyle differences among ethnicities could have confounded the results. But her study found these benefits to occur regardless of the ethnicity studied.
The study led by Gunter likewise found a lower death risk from various ailments, including digestive, circulatory and liver disease. The relationship was the same regardless of country, the study found. It was funded by the European Commission Directorate-General for Health and Consumers and International Agency for Research on Cancer.
The studies make a significant contribution to knowledge about coffee and health, said professor Peter Adams from Sanford Burnham Prebys Medical Discovery Institute.
"It's good to know that not everything that gives you a buzz is bad for you," Adams said via email.
"These two publications extend the findings of previous studies indicating the apparent benefits of coffee drinking," he added. "While the data across these and previous investigations seems consistent and compelling, to be really convincing it is important to figure out how it works.
"As the authors note, coffee is a complex concoction, and caffeine itself does not seem to be responsible. Coffee does contain many other candidate molecules, for example anti-oxidants."
"However, recent studies have challenged the view that antioxidants are always beneficial. Oxidants may not cause ageing as previously thought, and antioxidants can even help cancer cells to survive."
"So until we figure out how it works, you can keep drinking coffee and stay off the expensive antioxidants from the pharmacy," he said.
Coffee is most renowned for its stimulant effect, provided by caffeine. However, individuals respond differently based on their genetics. Some people are metabolically fast at breaking down caffeine, others metabolise it more slowly.
This has health consequences. One of the few studies that showed some harm in coffee found that slow metabolisers who drank four or more cups of regular coffee a day experience a 36 per cent greater risk of nonfatal heart attacks.
However, fast metabolisers who drank that much coffee had a lower risk of heart attacks. The presumptive explanation is that the noncaffeine components of coffee exert beneficial effects, and fast metabolisers clear caffeine quickly enough to avoid harm from an excessive dose.