Researchers from Harvard University found that women who consumed two to three cups of caffeinated joe per day had a 15 percent lower risk of depression than non-coffee drinkers, while those who drank four-plus cups daily had a 20 percent lower risk. In general, women are more likely than men to be diagnosed with depression.
“Our results support a possible protective effect of caffeine, mainly from coffee consumption, on risk of depression,” the researchers wrote Monday in the Archives of Internal Medicine. The researchers followed more than 50,000 participants in the Nurses Health Study — one of the largest women’s health studies in the U.S — for 10 years.
But the study’s authors cautioned that their results must be replicated before it’s possible to draw any firm conclusions about caffeine and depression risk — particularly in terms of any causal mechanisms that might be at play.
“Caffeine is known to affect the brain,” study co-author Dr. Albert Ascherio, a professor of epidemiology and nutrition at the Harvard School of Public Health, offered as one possible explanation. “It modulates the release of mood transmitters.” He pointed out that previous studies have shown a link between coffee and decreased suicide risk, though as the National Institute of Health points out, caffeine may cause or worsen anxiety issues.
Dr. John Greden, executive director of the University of Michigan’s Comprehensive Depression Center, agreed that the Harvard study — as well as others that have come before it — suggest interesting possibilities in terms of a link.
“Clinical depression is found in one out of every six people, roughly, and caffeine is one of the most widely used stimulants in the world,” he said. “If you put those two together, it has always been a logical question to ask, ‘Is there a connection?'”
But Greden cautioned that the current study has its limitations, too, particularly in terms of the participant pool.
“The women they studied had an average age of above 60, and most depressions start young,” he said. “So in a strange way, this is probably a very protected group, given the fact that none had depression at the start of the study.”
The results of the new study center on the potential impact of caffeine from coffee — not caffeine in general — namely because among the participants, the amount of caffeine consumed from other sources was too small for any stable results.
Ascherio said this should be just one of many additional considerations in future research that looks at possible caffeine and depression links.
In the meantime, he said the study should not prompt non-coffee drinkers to take up the habit. It could, however, offer current coffee drinkers some reassurance.
“I’m not saying we’re on the path to discovering a new way to prevent depression,” he said. “But I think you can be reassured that if you are drinking coffee, it is coming out as a positive thing.”