Last week there were a flurry of news stories about a study that linked drinking soda with depression, and that the link with diet soda was even stronger. The story in US News describes the work pretty well but the story was even covered in The Onion.
The work was by Honglei Chen, M.D., Ph.D. and 6 collaborators from the National Institutes of Health.They did a prospective study meaning that they knew from the outset what they wanted to study, rather than a retrospective study where they examine already existing data.
Starting in 1995, they surveyed 263,925 older U.S. adults for their beverage consumption. Then, in 2004-2006, they asked the group if they had had any diagnosed depression since the year 2000. And 11,311 (about 4%) of that group reported that they had been diagnosed with depression.
They found that those drinking 4 or more cans a day of sweetened beverages were 1.3 times as likely as those who didn’t, and those drinking coffee only about .91 times as likely. Those drinking fruit punch were 1.38 times as likely and those drinking sodas 1.31 times as likely.
There was a slightly higher ratio of depression among those drinking diet sodas (1.31) versus those drinking sugar-sweetened sodas (1.22).
Note, however, that nearly 16% of adults over 65 are clinically depressed and 3% have major depression according to this study by Birrer, reported in the American Family Physician.
And the study reports a correlation between soda drinking and depression, but does not in any way prove that there is any cause for that depression in drinking sodas. In fact, depressed people may choose to drink more sodas!
But where exactly is the paper?
Well, that’s the problem. This is all from a press release from the American Academy of Neurology (AAN) describing a paper that will be presented at their March 16-23 meeting. And that press release is only about 200 words. The talk has not yet been presented and there is as of yet no peer reviewed paper to examine.
Generally, when you finish some research, you write a paper describing your work, but since publication can take a year or more after you are satisfied with the paper and submit it, you may very well want to give a presentation at a conference to get your work out there for discussion. Or you may first give the presentation and get feedback before writing the paper.
In fact, this can be very valuable, since discussions of your work at a conference can lead to suggestions for improvements and further work. This has not yet happened, so, while the paper appears to describe well-constructed work, it has not yet been discussed nor has it been subjected to peer review for publication.
So, to conclude, as Chen said in an interview with U.S. News,
“More research is needed to confirm these findings, and people with depression should continue to take depression medications prescribed by their doctors."