Flavonols in chocolate could be behind heart health benefits
blood pressure and improves insulin sensitivity in healthy people,
lending weight to its potential for heart health.
However an editorial suggests that studies in larger groups and in diabetic and hypertensive individuals are needed to confirm how chocolate benefits health.
Researchers from the University of L'Aquila in Italy compared the effect of dark and white chocolate on blood pressure and glucose and insulin responses in 15 healthy individuals.
They were randomly assigned to receive either 100g of dark chocolate, which contained around 500mg polyphenols, or 90g white chocolate, which presumably contained no polyphenols, for 15 days. After a cocoa-free washout phase of seven days, the subjects were crossed over to the other condition.
HOMA-IR, a measure of insulin resistance, was significantly lower after dark than after white chocolate ingestion and insulin sensitivity was significantly higher after dark than after white chocolate ingestion, write the researchers in this month's issue of the American Journal of Clinical Nutrition (vol 81, no 3, 611-614).
Although within normal values, systolic blood pressure was lower after dark than after white chocolate ingestion, they report.
Previous research has suggested that flavanols in cocoa could protect blood vessel health because of their antioxidant properties and increased nitric oxide bioavailability. Nitric oxide bioavailability also has a strong influence on glucose uptake, so the researchers theorise that flavanols may also exert positive metabolic effects.
However in an editorial in the same journal, Cesar G Fraga from University of California, Davis notes that it is not yet clear if the flavonols are responsible for this effect.
"Chocolate containing 500 mg polyphenol could contain a relatively high concentration of flavanols (100-200 mg)," he writes but says the researchers did not report how they determined this quantity of polyphenols.
"Therefore, the interpretation that flavanols and procyanidins contained in the dark chocolate used in this study may be associated with the observed health effects is tempting but remains speculative."
Also, while other data that have shown effects of flavanol on nitric oxide production, it is uncertain how flavanols increase the body's uptake of nitric oxide. Fraga cites three possible mechanisms for this effect, but notes that further research is needed to elucidate which ones are working.
