Chocolate linked to lower stroke and stroke mortality risk

Susan Jeffrey

February 12, 2010

Hamilton, ON - Good news for Valentine's retailers the world over: a new systematic review from Canadian researchers suggests higher chocolate consumption may be associated with a lower risk for incident stroke and stroke-related mortality [1].

Previous studies, most of them epidemiological, have shown varying effects of chocolate consumption on the risk for cardiovascular disease, but "less is known about the risk of stroke in association with flavonoid intake," the researchers, with first author Sarah Sahib (McMaster University, Hamilton, ON), write.

Results of two prospective cohort studies showed, respectively, a 22% reduction in stroke risk for those who had one serving of chocolate per week and a 46% reduction in stroke mortality from weekly consumption of flavonoids in 50 g of chocolate vs no consumption. A third study showed no association between chocolate intake and stroke or death.

However, the number of studies looking at this relationship was small, senior author Dr Gustavo Saposnik (St Michael's Hospital and the University of Toronto, ON) said in an interview. "We need more prospective studies that specifically identify the type of chocolate and the amount, including the amount of flavonoids included in the composition of the chocolate, to make more valid conclusions," he said.

The results are published online February 17, 2010 in advance of their planned presentation at the upcoming American Academy of Neurology 2010 Annual Meeting in April.

Varying effects

Sahib et al reviewed studies published between 2001 and 2009, using search terms including flavonoids, flavanols, isoflavones, and anthocyanidins, as well as stroke and mortality.

"We found 88 publications, among them three prospective studies, and another retrospective study providing some information on the effect of chocolate consumption on the incident risk of stroke," Saposnik said. "Two of these studies show a reduction in the incident risk of stroke, and the other two didn't show any substantial difference."

They conclude that further prospective studies are needed "to assess whether the benefit of chocolate-based flavonoid consumption truly lowers stroke risk or whether the apparent benefit is biased by a healthy-user effect."

Investigation a challenge

However, while more data on this link would be helpful, Saposnik pointed to several challenges to doing these kinds of studies. First, it is important to document the actual content of flavonoids or other substances thought to be active in the chocolate being consumed.

"There are some studies that compare the content of flavonoids for different food elements and antioxidant capacity," he said. Dark chocolate has the highest flavonoids and procyanidins, which have been associated with lower cardiovascular risk, and dark chocolate also has the highest antioxidant capacity.

Still, there are varying types of chocolate, and the amounts that are required to affect stroke risk may bring a load of sugar and fats that may work counter to the beneficial effects. "Fifty grams of chocolate per day is a significant amount," he notes.

Finally, large longitudinal studies are also expensive, and funding for them scarce, which may explain why much of the evidence is coming from epidemiologic studies, he added. One alternative may be to conduct smaller studies, looking the effects of consuming controlled amounts of chocolate on some intermediate biomarker of stroke risk.

The study received no commercial support. The authors have no disclosures.

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