Ever since the 15th century, people have been drinking that oh so stimulating bitter drink of choice, coffee. In the morning, there’s nothing quite like it to put a spring in your step. Is coffee good for you? The evidence is a bit mixed. Caffeine giveth and it taketh away—if insomnia is a big problem, you are better off without. Anxiety can also be stirred up by a cup of joe.
But what does the research say about, say, depression and coffee? A new piece of epidemiology from the Nurses' Health Study was published in the Archives of Internal Medicine in 2011: Coffee, Caffeine, and Risk of Depression Among Women.
Some facts from the article—80% of the caffeine in the world is consumed as coffee. Prospective studies of men and caffeine use showed a strong inverse association between coffee drinking and depression, with no association for tea or cola. So the more the merrier, but forget those weaker brews. Three cohort studies in the past have shown an inverse relationship between coffee consumption and suicide. In one Finnish study, there was a J-shaped curve, with those consuming more than 7 cups of coffee daily at somewhat higher risk of suicide, and those consuming moderate to very little coffee also at higher risk. "Heavy" moderation (if moderation really means 7 cups of coffee a day…) was associated with the lowest risk.
In the Nurses' Health Study following 121,700 American female nurses over time, women filled out questionnaires every two years. 97,000 filled out questionnaires in 1996, ’98, or 2000, and those with no history of depression at that time (50,739 women) (those with unknown history were excluded) were followed over the next decade.
Regular coffee drinkers in this cohort were more likely to be smokers, drinkers, and not go to church. They also tended to have lower rates of diabetes and obesity. Average consumption for the entire group was about 1&1/2 cups of coffee a day.
Among the 50,739 women, about 2600 developed clinical depression in the 10 year period. There was a dose dependent, inverse relationship between the amount of coffee consumed and the risk of developing depression over the years, the same as in previous epidemiological studies of coffee and depression from all over the world. When confounding variables (such as age, health, smoking, divorces, etc. etc.) were all adjusted for, the inverse relationship became even stronger! No associations were found between tea consumption, chocolate consumption, decaf coffee, or soda consumption and depression.
So what's up? Is coffee an antidepressant?
Well, maybe. This study is no randomized controlled trial, so causation cannot be determined, but caffeine (1,3,7-trimethylxanthine) has multiple neurotransmitter effects. You may be enjoying some of them this morning. One of the effects is to antagonize the adenosine A2A receptor. This is thought to be pro-dopamine. Dopamine is a stimulating, wake up, get out, and conquer the world sort of neurotransmitter. In addition, by reducing the effects of adenosine by antagonizing the receptor, caffeine might also be affecting the transmission of norepinephrine and serotonin, both known targets of antidepressant medicines.
Since coffee is known to cause insomnia and anxiety, both features of depression, a weakness of the study is that women prone to insomnia and anxiety might limit their intake of coffee, thus biasing the results so that women who can tolerate a truckload of coffee also happen to be the ones less prone to depression.
But… all told, it seems that this study is another notch in coffee's bedpost. Though less than 8 cups a day seems prudent. And I really can't recommend Mountain Dew :)
Copyright Emily Deans, MD