Plant flavonoids, a group of natural substances found in fruits, vegetables, and certain beverages, have garnered significant attention due to their wide-ranging and substantial biological effects. Flavonoids encompass various subgroups, including flavanols, which are notably present in cocoa and chocolates. These compounds have demonstrated specific activities in vitro that are crucial for vascular health, particularly concerning endothelial function, the synthesis of endothelium-derived nitric oxide, platelet function, and cellular processes influenced by reactive oxygen and nitrogen species.
Flavanols and Vascular Health
In vitro studies have highlighted that flavanols can significantly impact vascular health. They promote the synthesis of nitric oxide, a molecule that plays a vital role in maintaining endothelial function. This effect is crucial as endothelial dysfunction is a precursor to various cardiovascular diseases. Additionally, flavanols influence platelet function and cellular processes modulated by reactive oxygen and nitrogen species, further contributing to cardiovascular health.
Epidemiological Evidence and the French Paradox
Epidemiological evidence linking flavonoid consumption to heart disease and mortality in humans is impressive yet often conflicting. A well-known example is the 'French paradox,' which refers to the observation that the French population, despite having a high-fat diet, does not exhibit a corresponding high rate of myocardial infarctions. Researchers have attempted to attribute this paradox to the consumption of red wine, rich in flavonoids. However, the evidence remains inconclusive.
Flavanols in Cocoa and Chocolate
Epidemiological studies examining the impact of flavanols consumed through cocoa and chocolate on cardiovascular risk are limited. Despite this, certain studies have indicated a significant influence of flavonoid-rich foods on cardiovascular health. For instance, a prospective study on mortality determinants after acute myocardial infarction (MI) revealed that patients consuming an average of 14 or more cups of black tea per week experienced a 39% reduction in mortality during a median follow-up of 3.8 years. Even moderate tea drinkers, averaging two cups per week, showed a 31% reduction. These associations persisted even after adjusting for usual risk factors.
Conflict in Study Results
The conflicting results in studies exploring the cardiovascular benefits of flavonoids can be attributed to various factors. These inconsistencies necessitate a focused review on the potential cardiovascular health benefits of flavanols in cocoa and chocolate. Identifying the mechanisms responsible for these effects can substantially aid in resolving the discrepancies observed in different studies.
Endothelial Dysfunction and Flavanols
Endothelial dysfunction is a critical factor in cardiovascular diseases. Studies conducted in vitro, in animal models, and in humans have provided growing evidence that flavonoids can positively influence endothelial dysfunction. The activation of nitric oxide synthesis appears to be the common pathway through which these natural products exert their beneficial effects. This discovery has its roots in the study of the Kuna Indians in Panama. These indigenous people, living on Caribbean islands, do not exhibit the typical rise in blood pressure with age, and hypertension is rare among them. Initially, researchers speculated a genetic protection; however, migration to Panama City, which led to the loss of this protection, pointed towards an environmental factor.
The Kuna Indians and Flavanol-Rich Cocoa
Further investigation revealed that the Kuna Indians consumed large amounts of flavanol-rich cocoa. Subsequent in vitro studies demonstrated that cocoa extracts could induce endothelium-dependent relaxation, prompting further research in healthy volunteers and patients with vascular risk or disease. One study showed that consuming flavanol-rich cocoa increased flow-mediated vasodilation of the brachial artery after five minutes of ischemia, correlating with biochemical evidence of increased nitric oxide bioavailability.
In another study, flavanol-rich cocoa induced significant dilation of the finger vessels in normal volunteers, an effect completely reversed by an arginine analogue that blocks nitric oxide synthesis. These findings underscore the potential of flavanol-rich cocoa in improving vascular function through mechanisms involving nitric oxide synthesis.
Conclusion
In summary, the biological effects of plant flavonoids, particularly flavanols found in cocoa and chocolates, are substantial and multifaceted. Despite conflicting epidemiological evidence, studies highlight their potential cardiovascular benefits, especially through mechanisms enhancing endothelial function and nitric oxide synthesis. These insights not only advance our understanding of flavonoids' health benefits but also underscore the importance of dietary choices in cardiovascular health.
The Cardiovascular Benefits of Plant Flavonoids: Insights from Cocoa and Chocolate
