BOSTON, Nov. 17 (UPI) -- For years, studies have cautiously shown that moderate amounts of coffee can be beneficial for brain and liver health, as well as reduce the risk for several types of cancer.
Researchers have now linked three to five cups of coffee per day to an overall lower risk of premature death, according to a new review of data on more than 200,000 health professionals.
The lowered risk was associated with a moderate amount of coffee, as opposed to those who drink only a cup or two, or no coffee at all, who did not see the health benefits. When researchers adjusted for those who smoke cigarettes, the benefits of all that coffee were even greater.
The idea that coffee can prevent the development of adverse health conditions, as studies just this year have shown it is good for brain health in older people, cancels out liver damage from over-consumption of alcohol, and may improve colon cancer survival.
"Bioactive compounds in coffee reduce insulin resistance and systematic inflammation," said Ming Ding, a doctoral student in the Harvard T.H. Chan School of Public Health, in a press release. "That could explain some of our findings. However, more studies are needed to investigate the biological mechanisms producing these effects."
Harvard researchers reviewed data for 74,890 women in the Nurses' Health Study, 93,054 women in the Nurses' Health Study 2, and 40,557 men in the Health Professionals Follow-up Study. Participants completed food questionnaires every four years for three decades, providing researchers with coffee consumption data.
Drinkers of both caffeinated and decaffainated coffee saw a positive effect on their health. Overall, people who drank 1.1 to 3 cups of coffee per day had a 9 percent lower risk of dying than non-drinkers, while those downing 3.1 to 5 cups per day had a 7 percent lower risk of dying. More than 5 cups per day saw a 2 percent increase in their risk of dying.
Unlike previous studies, however, researchers also considered smoking. When taking cigarettes out of the mix -- because many people who smoke also drink a lot of coffee -- the data showed that 1.1 to 3 cups per day led to an 8 percent drop in mortality and 3.1 to 5 cups per day had a 15 percent lower risk of death. Those drinking five or more cups were 12 percent less likely to die.
"We're not sure exactly how coffee is [linked] to all these benefits," said Dr. Walter Willett, a professor of epidemiology and nutrition at Harvard, told NPR. "The coffee bean itself is loaded with many different nutrients and phytochemicals. And my guess is that they're working together to have some of these benefits. We [see] similar benefits from caffeinated and decaffeinated coffee. That's important, because it suggests that caffeine is not responsible for [the benefit]."
The study is published in the journal Circulation.