By Matt McMillen
MONDAY, September 26, 2011 (Health.com) — A few cups of coffee a day may help keep the blues at bay. According to a large new study, women who drink caffeinated coffee are less likely to become depressed—and the more they drink, the more their risk of depression goes down.
The study, which was published today in the Archives of Internal Medicine, included more than 50,000 women between the ages of 30 and 55 who periodically filled out surveys about their coffee consumption and health. None of the women had depression symptoms (or a history of depression) at the start of the study, but during the next 10 years roughly 5% received a depression diagnosis or began taking antidepressant medication.
Compared to women who drank little or no caffeinated coffee, those who averaged two to three cups per day were 15% less likely to develop depression, even after the researchers took into account a wide range of potentially mitigating factors including marital status, church or community participation, and various health measures. Drinking four cups a day was associated with a 20% lower risk of depression.
The study doesn't prove cause and effect, so there's no reason to believe that drinking cup after cup will actually prevent depression, the researchers say.
"There's no need to start drinking coffee," says study co-author Alberto Ascherio, MD, a professor of epidemiology and nutrition at the Harvard School of Public Health, in Boston. "The message is that coffee is safe to drink, with no adverse effects. That's really all that can be said."
Previous research, including a study published last year that was conducted among men in Finland, has linked caffeine consumption to a lower risk of depression and suicide.
"A couple of past studies found similar results," says Daniel Evatt, PhD, a psychiatry research fellow at the Johns Hopkins School of Medicine, in Baltimore, who was not involved in the new research. "This study validates the association, and it was done in the best possible way."
It's not clear why coffee might protect against depression. Some experts have speculated that the antioxidants in coffee may have health benefits, but in the new study people who drank only decaf were no more or less likely to be depressed than women who drank no coffee at all.
The caffeine might be responsible, but the researchers weren't able to confirm or deny this theory because there wasn't enough data available to determine whether drinking caffeinated tea or sodas is linked to depression risk in the same way as coffee consumption. Eighty-two percent of the study participants drank coffee, while only 13% and 6% drank tea and soft drinks, respectively.
Evatt, who studies the psychological effects of caffeine, is "not terribly convinced" that caffeine can prevent depression. "There's a very strong indication that there is a real relationship there, but that doesn't mean that coffee will stop depression," he says. "We need to come up with a hypothesis for the mechanism at work, and then try to see what's really happening."
Another possibility is that people who aren't depressed may simply be more drawn to coffee than their depression-prone peers. Non-depressed people tend to be more "behaviorally activated," and coffee drinking may therefore fit in better with their lifestyle, says Scott Bea, PsyD, a psychologist at the Cleveland Clinic who was not involved in the study.
Similarly, Bea adds, some depressed people may steer clear of coffee because it can heighten anxiety, which often goes hand in hand with depression.
"We shouldn't rush to the conclusion that I should drink more coffee if I don't want to be depressed," Bea says.
For his part, Evatt stresses that caffeine can have negative consequences for many people, whether they're experiencing depression symptoms or not.
"We shouldn't put caffeine in too positive a light," he says. "Some people have a relationship with caffeine that's similar to an addictive drug. I don't want to pin it as a public health problem, but people can become dependent on coffee and have troubling withdrawal symptoms."