Drink Coffee, Stay Happy?

Sept. 26, 2011 -- Some coffee drinkers may have a reason to smile -- or keep smiling.

Drinking several cups a day is linked with a lower risk of depression, according to a new study that looked only at women. The benefit seems to start at two cups a day.

The study is published in the Archives of Internal Medicine .

"We found that women with the highest coffee intake -- those in the top 20% -- had a 20% lower risk of developing depression," says researcher Alberto Ascherio, MD, DrPH. "The top 20% drank about the equivalent of four cups of coffee per day." Ascherio is professor of epidemiology and nutrition at the Harvard School of Public Health and professor of medicine at Harvard Medical School.

The link was not found for decaffeinated coffee.

Ascherio emphasizes that he found an association, not cause and effect. Depression affects twice as many women as men, he notes. About 20% of U.S. women will be affected during their lifetime.

A mental health expert cautions that the research finding should be viewed cautiously. "I wouldn't tell my patients to drink more caffeine based on this study," says Michelle Riba, MD, associate director of the University of Michigan Depression Center. She reviewed the study but was not involved in it.

Caffeine and Depression Risk

Ascherio and colleagues evaluated more than 50,000 women, average age 63. They were participating in the long-running Nurses' Health Study.

None had any depression at the start of the investigation in 1996. All answered questions about their caffeine habits through June 2006. "Women reported their consumption of coffee and other caffeine drinks, more or less every four years," Ascherio says. They noted their usual intake over the past 12 months.

The women also reported if they had clinical depression or if they began using antidepressant medication.

During the follow-up, 2,607 women developed depression.

Overall, the more coffee they drank, the less likely they were to become depressed. "We see a dose response," Ascherio tells WebMD.

Compared with women who drank one cup or less a week, those who had two to three cups a day had a 15% lower risk of depression. Those who drank four or more had a 20% lower risk.

What could explain the link? Ascherio cannot say for certain."We know for certain caffeine gets into the brain. It activates several neurotransmitters related to depression." Among them, he says, are dopamine and serotonin.

That happens short-term, he says. How that affects the risk of depression long-term is not known, he says.

Other research has found a link between coffee drinking and lower risk of Parkinson's disease and diabetes, Ascherio says.

The new findings are consistent with some earlier research. He says one study found suicide risk is lower among those who drink more coffee. A previous study by others found that men who drink coffee have lower risks of depression.