Eating flavanol-rich dark chocolate as part of a healthy diet may help lower blood pressure in people who have persistent high blood pressure for which no specific cause can be found (essential hypertension), say researchers.

Writing in the journal Hypertension, Dr David Grassi, from the University of L'Aquila in Italy, and colleagues explain that dark chocolate has been shown to decrease blood pressure and insulin resistance in healthy people. They therefore decided to see whether the confectionary could help reduce blood pressure levels in people with hypertension.

For their study, the researchers assigned 20 patients with essential hypertension, who had never been treated for the disorder, to either 100 g per day of dark chocolate containing 88 mg flavanols or 90 g per day of flavanol-free white chocolate, for a period of 15 days.

Flavanols are compounds found in certain foods, such as apples, tea, wine and cocoa, which may have potential heart benefits.

After a chocolate-free period, the groups were switched over to the alternative chocolate "treatment". All participants had systolic (during the heart beat) blood pressure of 140-159 mmHg and diastolic (between heart beats) blood pressure of 90-99 mmHg, and none had diabetes or smoked.

The researchers found that the participants' 24-hour systolic and diastolic blood pressure decreased after consumption of the dark chocolate by an average of 11.9 mmHg and 8.5 mmHg, respectively. The consumption of the dark chocolate was also associated with improvements in insulin resistance and reductions in levels of "bad" cholesterol.

None of these benefits, however, were seen after consumption of the white chocolate.

"The current study shows that consumption of flavanol-rich dark chocolate decreased daytime and nighttime BP [and] reduced insulin resistance," the researchers report.

However, they add: "It is important to note that the dark chocolate used in this and related studies differs markedly from the majority of commercially available cocoa or chocolate confectionery with very low flavanol content.

"Further caution is always warranted when considering dietary recommendations for foods high in fat and calories, especially for cardiovascular disease."