I’m always on the lookout for good studies that are misinterpreted by the media (see here and here for examples). Why is this important? Because those of us whose profession it is to translate research findings to the public tend to get smacked upside the head by media misrepresentations. The public gets so used to duelling research findings that they become skeptical about things we are really certain about (e.g., climate change).
If you read your newspaper or watched TV in the last week or so, you may have seen media reports on the relationship between chocolate and depression. Now I love chocolate, and I’m not ashamed to admit it. I spent a year living next to Switzerland, and I can name every brand produced in that country (and I had the extra pounds to show it).
So I got concerned when I read the headlines like this:
Chocolate May Cause Depression
Chocolate Leads to Depression?
Depressed? You Must Like Chocolate
It was a matter of minutes for us to find the original article in the Archives of Internal Medicine. (The abstract is free; unless you have access to a library, you have to pay for the article.) It’s clearly written, sound research. And it absolutely does not say that chocolate leads to depression (whew!). Indeed, the authors acknowledge that the study can’t tell us that at all.
The research used a cross-sectional survey of 931 subjects from San Diego, California, in which they asked people about both their chocolate consumption and their depressive symptoms. By “cross-sectional” is meant a survey that takes place at one time point. This is distinguished from a longitudinal survey, where the same people are measured at two or more time-points. Why is that important here?
Here’s why. What epidemiologists call “exposure” – that is, whatever might cause the problem (in this case, chocolate) – is measured at the same point in time as the outcome (in this case, depression). For that reason, we can’t be sure whether the chocolate preceded the depression, or the depression preceded the chocolate. They both are assessed at the same time. So we can never be sure about cause and effect from this kind of study.
Now, a longitudinal study is different. The advantage of a longitudinal study is that you can detect changes over time. In this case, you could establish depression and chocolate consumption levels at Time 1, and keep measuring them as they continued over time. For example, if some people who weren’t depressed at Time 1 started eating chocolate and became depressed at a later point, we have stronger evidence of cause and effect.
As good scientists, the authors acknowledge this fact. They note that depression could stimulate cravings for chocolate as a mood-enhancer, that chocolate consumption could contribute to depression, or that a third factor (unknown at this point) could lead to both depression and chocolate consumption (my own pet theory: Valentine’s Day!).
In the interest of full disclosure, some of the media did get it right, like WebMD’s: succinct More Chocolate Means More Depression, or Vice Versa. But because some media sources jump to the most “newsworthy” (some might say sensationalist) presentation, there’s no substitute for going back to the actual source.
Finally, let me say that there is only one way to really establish cause and effect: a randomized, controlled trial. One group gets chocolate, one doesn’t, and we look over time to see who gets more depressed.
Sign me up for the chocolate group!
Sadly, the media frequently offers us a skewed version of research results. It seeks something exciting to write about, and this can lead to misinterpretation or over-interpretation of the actual research. Many of the articles written in the popular media on the topic of chocolate and its putative health effects exemplify this problem. The research is often over-simplified to allow for a catchy title, and leads the reader to an exciting, but often misleading, conclusion. Unfortunately the public seldom gets an accurate and balanced perspective when they rely only on short articles in the popular media as their source of health information.