I'm really falling behind my stack of papers. Fortunately, life is good and busy, and there are always new, catchy songs to listen to:
The Temper Trap: Fader
That song really puts a spring in my step. Rather like a strong cup of coffee. Full disclosure - more of a tea person, but I've been known to drink a cup of joe every now and again. Maybe I ought to drink a bit more… the evidence is mixed, frankly. And certainly I can't tell you how many times I've had patients complain of insomnia, only to find out they are drinking 6 large iced coffees a day, or 12 Mountain Dews (no matter how much I exercise, I don't seem to be able to take this weight off, doctor…).
But what does the research say about, say, depression and coffee? A brand spanking new piece of epidemiology from the Nurses' Health Study was published in the Archives of Internal Medicine this month - Coffee, Caffeine, and Risk of Depression Among Women.
Some facts from the article - 80% of the caffeine in the world is consumed as coffee. Interesting. Prospective studies of men and caffeine use showed a strong inverse association between coffee drinking and depression, with no association for tea or cola. Three cohort studies showed an inverse relationship between coffee consumption and suicide (though in a Finish study, there was a J-shaped curve with both very high (>7 cups of coffee daily) and low consumption of coffee seemingly less protective than moderate amounts.)
So, in the Nurses' Health Study (following 121,700 American female nurses starting in 1976), 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 whole group was about 1&1/2 cups of coffee a day.
Among the 51,000 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. When covariates (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?
I Know What I Am: Band of Skulls
Well, maybe. This is no randomized controlled trial, so causation cannot be determined, but caffeine (1,3,7-trimethylxanthine) antagonizes the adenosine A2A receptor. This is thought to have pro-dopamine effects. By taking out adenosine, we 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 :)