They said people who were depressed ate an average of 8.4 servings of chocolate per month, compared with 5.4 servings among those who were not.
And people who had major depression based on results of a screening test ate even more -- 11.8 servings per month. A serving was considered to be one small bar, or 1 ounce (28 grams), of chocolate.
"Depressed mood was significantly related to higher chocolate consumption," Dr. Natalie Rose of the University of California, Davis, and University of California, San Diego, and colleagues wrote in the Archives of Internal Medicine.
Many people consider chocolate a mood-booster but few studies have actually confirmed the connection between the confection and mood. And most studies have looked only at women.
Rose and colleagues studied the relationship between chocolate and mood among 931 women and men who were not using antidepressants. People in the study reported how much chocolate they consumed and most also completed a food frequency questionnaire about their overall diet.
Their moods were assessed using a commonly used depression scale. What they found was a marked association between chocolate consumption and depression. And unlike other studies that looked only at women, the link was true of both men and women.
What the study could not say was why people who are depressed eat more chocolate.
It could be that depression stimulates chocolate cravings, and people eat chocolate as a sort of self treatment, confirming some studies on rats that suggest chocolate can improve mood, the authors said.
Or, it could be that depression may stimulate chocolate cravings for some other reason without providing any mood benefit. People in the study did not have any such "treatment benefit" from chocolate, the team said.
And they said it may be that eating a lot of chocolate actually causes people to feel depressed, another possible explanation for the association they saw in the study.
It may be something physiological about chocolate, such as providing additional antioxidants. Or the mood-boosting effect of chocolate could be fleeting, like the temporary euphoria from drinking alcohol, leaving people feeling even lower after the brief euphoria has passed.
"Distinguishing among these possibilities will require different study designs," the team said.
They said future studies will be needed to determine whether chocolate is a cause of depression, or a temporary salve.
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