Chocolate linked to depression (or vice versa)

The Aztecs consumed chocolate as a beverage and called it bitter water. Linnaeus, who had more sense, named it Theobroma, the food of the gods. Evidently, the gods (if not the Aztecs) were a bit depressed – a recent study by Beatrice Golomb and her colleagues concluded that depressed people consume more chocolate. I am not surprised.

As reported in the LA Times, Science Daily, and elsewhere, Dr. Golomb and her colleagues examined the chocolate consumption of 931 participants who were involved in an epidemiological study. None of the participants had diabetes or cardiovascular disease, and none was on antidepressants.

The participants self-reported their chocolate consumption using what I take to be a well known and apparently well documented metric, the Fred Hutchinson Food Frequency Questionnaire. The study measured depression using another metric, Center for Epidemiological Studies–Depression Scale. People who scored higher on the depression scale also consumed more chocolate per week – the equivalent of about 8, 1-ounce servings per week (that is, approximately 8, 28-gram servings, in God’s units).

The study postulates no causative effect, either way, between chocolate consumption and depression. The authors note that there are comparatively little caffeine and theobromine in chocolate, and they did not find a correlation between caffeine and depression. Indeed, the LA Times quotes a food psychologist, Marcia Levin Pelchat, who argues that the effect is learned, not biochemical. That is, according to Dr. Pelchat, we train ourselves to eat chocolate when we are depressed. If that is so, then the correlation is effectively cultural.

There are a number of problems with this study, many of which are mentioned forthrightly in the article. The authors were not, however, data dredging: They stated a hypothesis, that consumption of chocolate would correlate with depression, and examined the data to confirm or disconfirm their hypothesis. They did not search high and low for apparent correlations with high statistical significance (low p-value), and they demonstrated a dose-response relationship (I thought, though, that a graph of chocolate consumption versus depression score would have been more useful than merely dividing the depression scores into 2 categories). The most troublesome aspect of this study to me (as a sometime metrologist), however, is that they report the standard deviation of their data sets but make no effort to include the standard uncertainty of either metric. My guess is that if they had calculated the combined standard uncertainty, their 95-% confidence intervals would have overlapped considerably.

Well, no, I take back some of what I just said. The most troublesome aspect is that they did not distinguish between proper chocolate and milk chocolate. Whereas I will admit that milk chocolate is better than no chocolate whatsoever, I want to know whether halfway-decent chocolate is better at curing my depression than insipid milk chocolate. I spend a lot of money every year on dark chocolate bars, and (my dental health notwithstanding), I want to know if it’s doing me any good.

Reference. Mood Food: Natalie Rose, Sabrina Koperski, and Beatrice A. Golomb, “Chocolate and Depressive Symptoms in a Cross-sectional Analysis,” Arch. Intern. Med. 170(8):699-703 (2010); Subscription required.

Acknowledgment. Thanks to Beatrice Golomb for providing a reprint of her article almost instantaneously.