Coffee, red wine, and the Mediterranean diet. To the list of dietary factors that may reduce the risk for stroke, add this guilty pleasure — chocolate. Women who consumed the largest amount of chocolate (more than 50 grams/week) were found to have a significant reduction in total stroke, cerebral infarction, and hemorrhagic stroke, a team of Swedish investigators wrote in a research letter in the Oct. 18 online edition of The Journal of the American College of Cardiology.
Susanna Larsson, PhD, of the Division of Nutritional Epidemiology at the National Institute of Environmental Medicine in Sweden, and colleagues based the association on an analysis of data from the population-based Swedish Mammography Cohort, comprising 39,000 women. In the fall of 1997, the women completed a self-reported questionnaire that asked them about nearly 350 items regarding their diet, including chocolate consumption, and lifestyle habits.
Using the Swedish Hospital Discharge Registry, the authors reviewed the incident cases of stroke between Jan. 1, 1998 and Dec. 31, 2009 — including diagnoses for cerebral infarction, intracerebral hemorrhage, subarachnoid hemorrhage, and unspecified stroke. For their analysis, Dr. Larsson and co-authors excluded at baseline women with a history of chronic disease, such as stroke, coronary heart disease, cancer or diabetes mellitus.
Among their findings, chocolate consumption was inversely associated with the risk of total stroke, cerebral infarction, and hemorrhagic stroke. For women who ate about 50 g/week of chocolate (equivalent to one small chocolate bar), the relative risks were 0.86 (95% CI: 0.77 to 0.96) for total stroke, 0.88 (95% CI: 0.77 to 0.99) for cerebral infarction, and 0.73 (95% CI: 0.54 to 0.99) for hemorrhagic stroke. The difference in risk estimates for cerebral infarction and hemorrhagic stroke was not significant (p = 0.28).
What about chocolate might be neuroprotective? “The flavonoids and some of the other compounds [in chocolate] may have antioxidant or anti-inflammatory properties, and therefore help alleviate the low-density lipoprotein cholesterol oxidation.. The other theory, as the authors stated, would be that it stabilizes the endothelial cells or platelets,” said Joshua Z. Willey, MD, assistant professor of neurology (stroke) at Columbia University School of Medicine, who has been involved in analyzing clinical risk factors for cerebrovascular disease in the population-based Northern Manhattan Study. Dr. Willey, who was not involved with the current study, compared the theories about chocolate to those that have been suggested about coffee, red wine, and other dietary factors.
The magnitude of the association [in the study] is pretty strong, using a large cohort and an extensive dietary questionnaire, Dr. Willey said. The study did a very good job adjusting for risk factors in their multivariable analysis, and they looked at both ischemic and hemorrhagic stroke, and at both of them combined, he noted, a strength lacking in many other stroke studies.
But like other studies reporting an associative reduction in risk for disease, experts said the current results, while interesting and worth further study, merit cautious interpretation. There are confounding factors to consider, for example, the overall health, socioeconomic status, and lifestyle of the population.
In fact, the authors listed the study's prospective design and self-reporting as potentially limiting factors that could have influenced the results. “Although we adjusted for major risk factors for stroke, we cannot exclude the possibility that our results may have been affected by residual or unmeasured confounding,” they wrote.
IS THE ASSOCIATION VALID?
“This [report] is still preliminary,” Gustavo Saposnik, MD, director of the Stroke Research Unit, Mobility Program and adjunct scientist at the Li Ka Shing Knowledge Institute at St. Michael's Hospital in Toronto, Ontario, told Neurology Today. It provides information about a potential association and should not imply causation, he said, stressing that it is the result of a secondary analysis that has generated an associative idea, rather than a response to an initial hypothesis.
The study was initially designed not to identify this association, he pointed out, but to include almost 40,000 women who underwent mammograms. “At the end of the day, it's important to bear in mind that the research question for this study was not related to chocolate consumption.”
Dr. Saposnik is currently preparing a meta-analysis of the evidence regarding chocolate consumption and the risk for stroke.
Dr. Willey speculated that socioeconomic status, for example, might be considered as an unmeasured contributing factor. “Depending on your socioeconomic status, you may actually eat chocolate on a frequent basis because you can actually afford it….Or, if you eat a particular amount of chocolate, it indicates a certain healthy lifestyle. That was my concern, which I think they can't fully adjust for. I think we'll need more data to see if this association is strong in accounting for that type of confounding.”
Dr. Willey pointed out that that it was unclear whether the questionnaire was representative of lifelong habits in these women — where people would eat the same things (including amount of chocolate), drink the same things, for a number of years, he said. “In younger people, who eat a lot of chocolate for example, it may actually go along with having a little bit more of a sweet tooth and being a little more overweight, and having more insulin resistance,” which may put them at a higher risk of stroke — not a reduced risk.
Another aspect worth considering, Dr. Saposnik said, is that 50 grams of chocolate in a week is not a huge amount. “It's half a large bar of chocolate,” which is consistent with the recommendations of general physicians to eat in moderation.
“I'm not ready to tell people to actively eat chocolate based on this study, but it adds to the evidence that certain aspects of diet, such as chocolate, coffee, and so on, could be part of a good primary prevention or secondary prevention strategy for stroke,” Dr. Willey said.
Dr. Saposnik said a prospective study to see whether chocolate consumption is associated with a lower cardiovascular risk could be a next step. This would include measuring the different levels of flavonoids, for example. But he questioned whether that approach was feasible. “Who is going to give chocolate during a period of time to one group of people and withhold it from another?” he asked. “The ideal situation would be to do a randomized study, but due to similar limitations it's unlikely to happen.”
Dr. Willey suggested that the next study should look for the association in both men and women and see if the results could be replicated in a representative US population. Would the association also hold in populations of lower and higher socioeconomic status or depend on levels of exercise?
This is an “interesting study,” he said. “Let's see if we get more people to replicate this before we start recommending chocolate for routine clinical care.”