We've never liked diet soda (please do not fact-check this with our college roommates), and now we have one more excuse to stay the hell away from it. According to a preview of a study coming out in March, people who drink four or more cans of soda each day were 30 percent more likely to be diagnosed with depression later on. Diet soda drinkers were even more likely than that to be depressed. And coffee drinkers -- well, coffee drinkers are apparently hyped up enough to be happy. They were 10 percent less likely to get depressed.
So, what does it all meeeeean? The study had more than 200,000 people in it, so that’s a good indication that there’s something interesting going on here. But Smithsonian does a good job of tackling the eternal causation/correlation dilemma:
Does this mean you should stop drinking diet Coke and starting chugging coffee immediately? Probably not. This type of suggested link between two seemingly unrelated factors is an ideal time to bring up the difference between causation and correlation. Do the ingredients in both diet sodas and normally-sweetened drinks trigger changes in brain chemistry that lead to depression? Or are people with the tendency to become depressed simply more likely to drink these beverages in the first place?
Without the full paper, it’s hard to know for sure—we don’t know if the study’s authors controlled for all relevant factors, making sure to compare study participants who were alike in all ways except for their beverage consumption.
Does drinking a lot of diet soda make you depressed, or do depressed people drink a lot of diet soda? Or do depressed people drink a diet soda, feel terrible about the state of the world because that stuff tastes so disgusting, and then drink more diet soda?