Others had previously shown that eating chocolate correlated with various positive health outcomes, but few had explored the treat’s effect on the brain and behavior.

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In the mid 1970s, psychologist Merrill Elias began tracking the cognitive abilities of more than 1,000 people in New York state. The goal was specific: Observe the relationship between people’s blood pressure and brain performance. And for decades he did that, eventually expanding the Maine-Syracuse Longitudinal Study (MSLS) to observe other cardiovascular-risk factors, including diabetes, obesity and smoking.

There was never an inkling that his research would lead to a discovery about chocolate. And yet, 40 years later, it did.

Late in the study, Elias and his team had an idea: Why not ask participants what they were eating too? Diet, after all, had been shown to affect the risk factors Elias was already monitoring. Plus, researchers had a large pool of participants at their disposal.

The researchers incorporated a new questionnaire into the sixth wave of their data collection, which spanned the five years between 2001 and 2006 (there have been seven waves, each conducted in five-year intervals). The questionnaire gathered information about the dietary habits of the participants, and the dietary habits revealed an interesting pattern.

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“We found that people who eat chocolate at least once a week tend to perform better cognitively,” said Elias. “It’s significant; it touches a number of cognitive domains.”

The findings, chronicled in a new study published last month, come largely thanks to the interest of Georgina Crichton, a nutrition researcher at the University of South Australia, who led the analysis. Others had previously shown that eating chocolate correlated with various positive health outcomes, but few had explored the treat’s effect on the brain and behavior, and even fewer had observed the effect of habitual chocolate consumption. This, Crichton knew, was a unique opportunity.

Not only was the sample size large — a shade fewer than 1,000 people when the new questionnaire was added — but the cognitive data was perhaps the most comprehensive of any study ever undertaken.

In the first of two analyses, Crichton, along with Elias and Ala’a Alkerwi, an epidemiologist at the Luxembourg Institute of Health, compared the mean scores on various cognitive tests of participants who reported eating chocolate less than once a week and those who reported eating it at least once a week. They found “significant positive associations” between chocolate intake and cognitive performance, associations that held even after adjusting for variables that might have skewed the results, including age, education and cardiovascular-risk factors.

In scientific terms, eating chocolate was significantly associated with superior “visual-spatial memory and [organization], working memory, scanning and tracking, abstract reasoning and the mini-mental state examination.”

Crichton said that such functions translate to everyday tasks, “such as remembering a phone number, or your shopping list, or being able to do two things at once, like talking and driving at the same time.”

In the second analysis, the researchers tested whether chocolate consumption predicted cognitive ability, or if it was the other way around: that people with better-performing brains tended to gravitate toward chocolate.

“It’s not possible to talk about causality, because that’s nearly impossible to prove with our design,” Elias said. “But we can talk about direction. Our study definitely indicates that the direction is not that cognitive ability affects chocolate consumption, but that chocolate consumption affects cognitive ability.”

Elias said the research isn’t finished. There are more questions to answer. “We didn’t look at dark chocolate and lighter chocolate separately,” he pointed out.

“We also only looked at people who were eating chocolate never or rarely versus once a week or more than once a week,” he added. “I’d really like to see what happens when people eat tons of chocolate.”