Q: Is there any evidence that drinking coffee or other caffeine beverages helps depression?

A: Yes, there are some studies that demonstrate an association between caffeinated coffee and a lower depression risk.

One example comes from the Nurses' Health Study that began more than 20 years ago. When the nearly 51,000 women were enrolled, none of them had depression. As just one small part of the study, researchers determined how many of the women later developed depression and compared their caffeine intake to determine whether it affected risk.

Within the next ten years, 2,607 women were diagnosed with depression or had started taking antidepressants. The researchers found an inverse dose-response relationship between caffeine intake and mood: the more caffeine a woman ingested per day, the lower the likelihood that she developed depression during the study period. The women who were least likely to develop depression were drinking about five cups of coffee per day.

In a more recent study, researchers evaluated coffee consumption and depression risk in over 14,000 young adults. The study participants who consumed at least four cups of coffee per day showed a lower risk of depression than participants who drank less than one cup of coffee per day.

These researchers also assessed the association between regular and decaffeinated coffee consumption and the risk of depression. They did not find a reduced depression risk with any amount of decaffeinated coffee.

While the results of these studies are interesting, they do not prove that regular coffee or other sources of caffeine can prevent or treat depression.

Despite no proof, caffeine has a plausible biological explanation for why it might benefit people with depression. Caffeine gets absorbed in the stomach and small intestine and is then distributed throughout the body, including the brain. The amount circulating in the blood peaks 30 to 90 minutes after it's ingested, and just trace amounts are around eight to 10 hours later.

Once it reaches the brain, caffeine probably has multiple targets, but the main one seems to be adenosine receptors. After attaching to these receptors, caffeine sets off a chain of events that affects the activity of dopamine, an important neurotransmitter involved in mood. Caffeine also indirectly affects two other neurotransmitters, serotonin and acetylcholine, which can play an important role in depression.

The possibility that regular coffee might enhance mood and even be an adjunct to mild depression treatment is intriguing. It adds yet another to the growing list of positive associations of coffee drinking and health.

(Howard LeWine, M.D., is an internist at Brigham and Women’s Hospital in Boston and assistant professor at Harvard Medical School. For additional consumer health information, please visit www.health.harvard.edu.)