Chocolate, Correlation, Causation, and Depression

A recent study published in the Archives of Internal Medicine has attracted a lot of media attention. ‘Chocolate and Depressive Symptoms in a Cross-sectional Analysis‘ has been written up in a number of newspapers here in the United States, often in the ‘oddly enough’ news sections, which is where ‘whimsical’ news about scientific studies often seems to end up.

There’s kind of a long history of media outlets writing up studies on food and twisting or ignoring the conclusions of those studies. Contradictory information about food is readily available through the media and sometimes there are very serious problems with the framing of these ‘oddly enough’ food stories. Like the claims that red wine is good for your heart, which ignored the fact that most studies supporting this claim pointed out that you would have to drink a lot of red wine to achieve cardiovascular benefits.

Two chocolate bars, a Richfield's Dark with Raspberries, and a Whittaker's Dark Caramel, shown in their wrappers.

The chocolate study involved 1018 subjects from San Diego, 931 of whom were not taking antidepressants. Researchers used the Center for Epidemiologic Studies Depression Scale (CES-D) to gauge levels of depression among the participants, and then collected information about chocolate consumption. What they found is that people with higher scores on the Scale tended to consume more chocolate. For people with very high scores, chocolate consumption was doubled.

The conclusion?

Higher CES-D depression scores were associated with greater chocolate consumption. Whether there is a causal connection, and if so in which direction, is a matter for future prospective study.

The media jumped on this study with headlines like ‘Study links chocolate and depression.’ ‘Study: Chocolate and depression go hand in hand.’ ‘Say it ain’t so: Study links chocolate to depression.’ And so on. Some articles went right ahead and used the ’cause’ word.

These articles theorize that either depression triggers chocolate cravings, or chocolate makes people depressed. They’ve made the classic mistake of conflating correlation and causation. abby jean has talked about this problem elsewhere on FWD, discussing the problem of bias in studies and bias in the way people talk about scientific studies. Recently, I discussed some of the problems with tests administered to measure levels of depression in ‘Internet Use and Depression.’

There are a couple of questions which should be asked about a study like this. The first is how the sample was chosen. Because I can’t access the full text, I can’t answer this question (someone who has read the study is welcome to chime in in comments). One thing which is notable is that this study took place in the United States. Here in the States, eating chocolate to  improve mood is a learned behaviour, and thus I can’t say that I was terribly surprised to  learn that people in the US who appear to be depressed are eating more chocolate. Since this study took place in a country where people believe that there is a link between chocolate and mood, it’s possible that some observer bias was involved in this study.

People believe that chocolate will make them feel better when they’re down1. In other cultures, there are other comfort foods which people eat to make themselves feel better. It would be interesting to see a cross-cultural study. As it stands now, we know that chocolate consumption appears to be higher in depressed residents of San Diego, California.

Another question about this study is whether the researchers controlled for other dietary factors or behaviours. Apparently they did control for ‘common’ factors like caffeine and carbohydrates, but it’s unclear how far they drilled down. Is it possible that people with depression also eat a lot of, say, peas? Brazil nuts? It’s impossible to control for everything, of course, but food and diet are complex issues and we’re still learning a lot about how food works, the compounds in food, and how different foods interact.

Furthermore, the study was not long term. More meaningful results might be obtained with a more extended study tracking people over months or years. It would also be immensely helpful to have subjects keep complete food and activity diaries to generate a spread of data which could be used to look at other things which might be correlated with depression.

Chemically, chocolate is incredibly complex, especially when you start talking about all of the varieties of chocolate available. There could be something going on here, but it would take a lot more research to find out.

  1. The jury is out on this one science wise. Some studies suggest that compounds in chocolate are mood elevators although they may work only in the short term. Others suggest that there’s no effect on mood. Others suggest that compounds in chocolate might actually work the other way around. And, of course, many studies like to take the time to point out that chocolate makes people fat and fat is bad, ergo, people who eat chocolate will be sad because they are fat.

About s.e. smith

s.e. smith is a recalcitrant, grumpy person with disabilities who enjoys riling people up, talking about language, tearing apart poor science reporting, and chasing cats around the house with squeaky mice in hand. Ou personal website can be found at this ain't livin'.

7 thoughts on “Chocolate, Correlation, Causation, and Depression

  1. I actually don’t like chocolate much, so if I notice myself craving or eating a lot of dark chocolate, it’s a good sign that I am depressed. It’s not my only comfort food, but it’s different from the others in that it’s something I don’t like much when I am happy–the others, it’s more eating more of foods I do love.

    What a complicated thing to study, though. I don’t see any reason to assume a casual relationship might exist.

  2. I hate news media discussions about depression. They always end up leaving me irritated.

  3. One person on my livejournal f’list commented on this study, saying (paraphrased): “Depressed people like chocolate. In other news, tired people like coffee, and people with headaches like Advil..”

    And I agree about the great variety of chocolate (and cocao) products available. Standard American, commercially-available milk chocolate does nothing for my mood. But stirring a tablespoon of unsweetened cocoa powder into hot water and drinking that does lift my mood noticibly in a minute or two. May not last long, but a three minute boost out of the doldrums can help get me past a bit of writer’s block, for example. And the success of getting past the block can lift my mood for a longer period.

  4. This reminds me of a study that was splashed across the media a few years ago that claimed that dark chocolate helped CFS/ME. Actually the study had an incredibly small sample and to top it off the control group were given white chocoate dyed dark, which tastes totally different.

    But of course the media loves any study that allows abled people to tell disabled people what to do.

  5. I noticed when I was a young’un that I loved to eat M&Ms when I was sad. I liked them anytime, but they tasted especially good to me when I was upset about something. Now, I’m more a fan of quality dark chocolate, but I still crave that sometimes when I’m feeling low. I don’t know if it’s a particular mood-lifting effect of the chocolate, or simply the fact that I love chocolate and it’s a simple pleasure that might lift my mood slightly regardless of its effects.

    I’d be interested in seeing a study about chocolate consumption and gender. There’s a definite stereotype of sad or lonely women reaching for the chocolate–see the movie “Down With Love” for a silly example. I feel like I read somewhere that chocolate has more of a mood-lifting effect on women than men, but it was so long ago I have no idea if it was a reliable source or not.

  6. While I found the study you quote here pretty reductive and facile (or at least, the way it’s been reported to us, the public, has been) I don’t see anything wrong with or ableist about the assertion that food affects mood (and I say this as a woman with depression).

    Multiple scientific studies have shown that sugar is a painkiller and as the body experiences/processes mental and physical pain in the same way (can not seem to differentiate between the two, in fact) it could be extrapolated that sugar reduces emotional pain, that people who are in emotional pain consume it for this reason, and that a physiological craving is set up as a result.

    But it doesn’t need to be extrapolated — there are loads of studies which back up the theory.

    This new study just confirms that sugar elevates mood (then brings it crashing down hours later so you need another hit). It’s nothing to do with cocoa or compounds.

  7. I have access to the full text. It says 1018 subjects “from the San Diego area in California, without known cardiovascular disease, diabetes, or extremes of high or low level of low-density lipoprotein cholesterol, were screened for participation in a clinical study (examining noncardiac effects of reducing cholesterol level)”. If I’m reading that sentence correctly, the subjects were originally going to be used in a study of something else. I don’t know if this answers your question. I don’t see much else indicating where they got the subjects.

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