A cup of java in the morning — or at any time of day — can provide a quick (although short-lived) improvement in mood.
Scientists (and coffee drinkers) have known that much for years. On Monday, however, a team of Harvard University researchers reported in the Archives of Internal Medicine that consistent coffee consumption may also have a long-term positive effect on mood.
Specifically, they found that women who drank two to three cups of caffeinated coffee daily were 15 percent less likely to develop depression over a 10-year period than their peers who drank one cup or less per day. The effect was even greater — a 20 percent lower risk for depression — among those who drank four or more cups per day.
No similar association was found for decaffeinated coffee, a finding that suggests, said the study’s authors, that it’s the caffeine and not some other as-yet unidentified substance in the coffee that may be staving off the blues. Nor did the study find an association between a reduced risk of depression and the consumption of tea, sugary soft drinks or chocolate. The study’s authors speculated that although those products contain caffeine, the amounts are too small to have any long-term effect on mood.
American adults get about 80 percent of their caffeine from coffee.
Interestingly, previous studies have reported an association between caffeine consumption and a reduced risk of suicide — but only up to six or seven cups a day. Once consumption exceeded that amount, the risk of suicide increased again.
“It is possible that persons with more severe forms of depression used very high doses of coffee as a form of self-medication that was, nevertheless, insufficient to elevate their mood,” wrote the Harvard researchers in the current study.
For the current study, the researchers followed some 50,000 women in the on-going Nurses Health Study. At the start of the study (1996), the women’s mean age was 63 years, and none had symptoms of depression. By the end of the study (2006), about 2,600 of the women had developed depression.
Because this is what’s known as a prospective cohort study, it cannot prove that drinking coffee lowers the risk of depression. It can show only an association between the two. Unknown factors that have nothing to do with caffeine could also explain that association, as the study’s authors point out. It could be, for example, that women who are predisposed to depression instinctively turn away from coffee because they realize that drinking too much of it can make them anxious or interfere with their sleep.
Another caveat: the data for the study was collected from questionnaires, which can be unreliable.
For these and other reasons, the study’s authors warn that their findings need to be interpreted with caution. No one should be running out and self-medicating themselves with caffeine based on this research. In fact, too much caffeine can cause anxiety and insomnia, which may contribute to depression.
Still, the findings are interesting, particularly since modest consumption of caffeinated coffee has not been found to have detrimental health effects in terms of heart disease, for example, or cancer.
In an editor’s note that also appeared in Monday’s issue of the Archives of Internal Medicine, Dr. Seth A. Berkowitz, an internal medicine physician in San Francisco, wrote that the current study “makes an important contribution because it is, to my knowledge, the first large-scale study of coffee consumption to evaluate a mental health outcome in women.” But, he added, “it seems premature to recommend coffee consumption until studies with methodologies better able to determine causality are conducted.”