by Craig Weatherby
Foods rich in antioxidants called flavanols appear to reduce the risk of developing or dying from cardiovascular disease.
This effect is attributed in part to their anti-clotting powers and ability to increase production of nitric oxide, which helps keep arteries relaxed and open.
The only common foods high in flavanols are green tea, white tea, cocoa, and dark chocolate.
Now, a review of the existing epidemiological (health-and-diet) evidence suggests that habitual enjoyment of tea, cocoa, or dark chocolate may help people avoid stroke.
And a study in mice shows that the key flavanol antioxidant in tea and cocoa can reduce stroke-induced brain damage after the fact.
Study #1 - Evidence review links chocolate to reduced stroke risk
Last month, Canadian researchers linked regular chocolate consumption to reduced risk of stroke.
Their review of the existing evidence turned up three relevant population studies, two of which showed an association between eating chocolate and reduced risk of stroke.
The first study involved 44,489 people, and those who ate one serving of chocolate per week were 22 percent less likely to have a stroke than people who ate no chocolate.
The second study, conducted in 1,169 people, found that those who ate 50 grams (1.7 oz) of chocolate once a week were 46 percent less likely to die following a stroke, compared with people who ate no chocolate.
The third study showed no link between eating chocolate and risk of stroke or death.
Of course, no epidemiological study can prove that any food reduces the risk of stroke… such studies only show an association.
But new evidence from a mouse study shows that the main antioxidant in cocoa—and in green or white tea—shields nerve cells from stroke-induced damage.
Study #2 - Tea/cocoa antioxidant protects brains of stroke-stricken mice
Researchers at Johns Hopkins University in Baltimore have discovered that the main antioxidant compound in green tea and dark chocolate may protect the brain after a stroke (Shah ZA et al. 2010).
The flavanol-class antioxidant—called epicatechin (ep-eh-cat-eh-kin)—does it by increasing cellular signals known to shield nerve cells from damage.
Ninety minutes after feeding mice a single modest dose of epicatechin, the scientists induced an ischemic stroke by essentially cutting off blood supply to the animals' brains.
The animals fed epicatechin suffered significantly less brain damage than the ones that had not been given the compound.
Most treatments against stroke in humans have to be given within a two- to three-hour time window to be effective.
Likewise, epicatechin appeared to limit further neuronal (brain cell) damage when given to mice 3.5 hours after a stroke, but had no effect when given to them six hours after a stroke.
Lead author Sylvain Doré, Ph.D., says that epicatechin stimulates two previously well-established pathways known to shield nerve cells in the brain from damage.
When the stroke hits, the brain is ready to protect itself because these pathways—called Nrf2 and heme oxygenase 1—are activated.
As further proof that these are the pathways thought which it protects brain cells, epicatechin had no significant protective effect in mice that lacked them.
Eventually, Doré said, his research could lead to insights into limiting acute stroke damage and possibly protecting against chronic neurological degenerative conditions, such as Alzheimer's disease and other age-related cognitive disorders.
And Doré says the amount of epicatechin needed could be quite small, because the suspected beneficial mechanism is indirect:
“Epicatechin itself may not be shielding brain cells from free radical damage directly, but instead, epicatechin, and its metabolites, may be prompting the cells to defend themselves” (AAN 2010).
The epicatechin simply “jump-starts” the protective pathway that is already present within the cells.
Not all dark chocolates are created equally, cautioned Dr. Dore:
“The epicatechin found in dark chocolate is extremely sensitive to changes in heat and light. In the process of making chocolate, you have to make sure you don't destroy it. Only few chocolates have the active ingredient. The fact that it says ‘dark chocolate' is not sufficient” (AAN 2010).
The amount of dark chocolate people would need to consume to benefit from its protective effects remains unclear, which would require clinical trials.
Chocolate and heart health: Processing kills the benefit
Harvard scientists led by Norman Hollenberg, M.D., have been investigating the potential heart-health benefits of epicatechin by studying Panama's Kuna Indians, who live on remote islands, drink copious amounts of cocoa and have a very low incidence of cardiovascular disease.
Dr. Hollenberg's team found nothing unusual in the Kuna tribe's genes, and realized that when they moved to the mainland they were no longer protected from heart problems.
Researchers soon discovered that the Kuna regularly consume a very thick, bitter cocoa drink that's rich in epicatechin, but lose access to it when away from home.
Unfortunately, most cocoa is treated with alkali to reduce its bitterness and darken it.
This process, called “Dutching”, destroys most of cocoa's epicatechin… and almost all chocolate is made from Dutched cocoa powder.
Dark chocolate—defined as containing 60 percent or more cocoa solids—has twice the antioxidant capacity of milk chocolate.
And dark chocolate made from non-Dutched cocoa has more than twice the antioxidant capacity of dark chocolate made from Dutched cocoa.
This is why Vital Choice brand Organic Extra-Dark chocolate is made from non-Dutched cocoa.
And independent lab tests show that it is in fact high in epicatechin and other antioxidants in cocoa… including heart-healthy procyanidins, which give berries and grapes much of their antioxidant power.
- American Academy of Neurology (AAN). Can chocolate lower your risk of stroke? February 11, 2010. Accessed at http://www.eurekalert.org/pub_releases/2010-02/aaon-ccl020210.php
- Sahib S et al. Chocolate Consumption and Risk of Stroke [P06.011]; Poster Session VI: Cerebrovascular Disease: Epidemiology II; 62nd Annual Meeting of the American Academy of Neurology, Toronto, Canada, Thursday, April 15, 2010.
- Shah ZA et al. The flavanol (-)-epicatechin prevents stroke damage through the Nrf2/HO1 pathway. J Cereb Blood Flow Metab. Advance online publication, May 5, 2010; doi:10.1038/jcbfm.2010.53