Giana Angelo, Ph.D.
Most of the health benefits ascribed to chocolate are likely due to their flavonoids, dietary factors that belong to the general class of compounds known as phytochemicals, or plant chemicals. More than 5,000 varieties of flavonoids have been identified, and hundreds of flavonoids can exist in a single food. All flavonoids have the same basic polyphenol chemical ring structure, hence the occasional reference to flavonoids as polyphenols. Different flavonoids possess varying numbers of rings and chemical attachments, thus imparting different properties to the specific compound.
Due to their unique chemical structures, flavonoids may exert antioxidant, anti-inflammatory, and cytoprotective (cell protective) effects in humans. Consuming flavonoid-rich foods has been associated with a reduced risk of certain chronic diseases, particularly cardiovascular diseases (CVD).
Chocolate contains flavonoids belonging to the subclass called flavanols. The specific flavanols present in chocolate are catechins and procyanidins. Catechins are also present in tea, grapes, and berries; procyanidins are also present in grapes, berries, and red wine.
Flavanols in chocolate come from the cocoa. Dark chocolate contains approximately 43-63 mg flavanols per 100 grams (about 3 oz). However, differences in processing can greatly affect the amount of flavanols present in commercial cocoa-containing products.
A common and early event in CVD occurs when the endothelium—the inner lining of blood vessels—is damaged. Therefore, protecting endothelial function helps minimize the risk for atherosclerosis, heart attack, and stroke. Several small-scale randomized, placebo-controlled trials have been conducted to help determine what quantity of consumed flavanols benefits vascular health. Researchers found that ingesting a cocoa powder drink (containing 375 mg flavanols) twice daily for 30 days improved endothelial dysfunction and blood pressure in patients with coronary artery disease. In healthy adults, ingestion of 46 grams of dark chocolate (containing 250 mg flavanols) daily for 2 weeks improved endothelial function. Even as little as 6.3 grams of dark chocolate (containing approximately 30 mg of flavanols) consumed daily for 18 weeks lowered blood pressure in healthy adults with above-optimal blood pressure.
These studies demonstrate that the amount of flavanols associated with beneficial effects is achievable through dietary consumption of cocoa or cocoa-containing products. It is important to note that flavanols in dark chocolate are found with other substances, such as fat, sugar, caffeine, and various additional phytochemicals.
A recent meta-analysis reported in the British Medical Journal has raised concern about the safety of calcium supplements, either alone or with vitamin D, on the risk of cardiovascular events like strokes and heart attacks. Specifically, the meta-analysis reported an increased risk for myocardial infarction—heart attack—in women taking calcium supplements. A “meta-analysis” is a statistical method that combines the results from several randomized controlled intervention trials that address similar questions. Although the meta-analysis raises an issue that needs further attention, there is insufficient evidence available at this time to definitively refute or support the claims that calcium supplementation increases the risk of cardiovascular diseases (CVD).
CVD is a broad term that encompasses many diseases affecting the heart and blood vessels. In the meta-analysis, the slight negative effect of calcium supplementation was seen with myocardial infarction in particular (approximately 25% increase in risk over five years of supplementation). In an earlier intervention trial by the same researchers, calcium supplementation had variable effects on other cardiovascular endpoints, including a beneficial effect on angina, which is chest pain caused by reduced blood flow to the heart and a common symptom of coronary artery disease. Why the authors removed angina from the recent meta-analysis was not explained and raises concerns.
The risk of myocardial infarction was statistically significant only at low to moderate calcium intakes, not at high levels of calcium intake. Moreover, those subjects with the highest intakes of calcium (>1,000 mg/day) had the lowest rates of death from all causes. This suggests that high calcium intake is protective overall. Why only a moderate dose of calcium would increase the risk of myocardial infarction is unknown.
Last updated May 2012