The cocoa bean is naturally high in flavanols—plant chemicals thought to protect from oxidative stress and other types of damage. While the process of creating cocoa and chocolate can often reduce the flavanol content, flavanol-rich cocoa or chocolate may improve cognitive function for elderly people. The benefits, however, are very small and specific. Whether it can protect against dementia is even less clear. On the plus side, safety concerns are minor and are generally limited to the caffeine and theobromine content, as well as the number of calories.
A few clinical trials have tested high-flavanol cocoa in elderly people, while two observational studies have reported mixed results on the potential link between chocolate intake (regardless of flavanol levels) and the rate of cognitive decline. Our search found:
• 1 systematic review of clinical trials on mood or cognition
• 3 small clinical trials in elderly people
• 2 observational studies on chocolate intake and cognitive decline
• At least 3 preclinical studies
A handful of small clinical trials have suggested that while cocoa and cocoa flavanols might slightly improve cognitive function, most aspects of cognition are unaffected . Cocoa or its flavanols may increase blood flow to the brain , which often decreases with aging  and in neurodegenerative diseases such as Alzheimer's . The flavanols in cocoa may not be required for this effect . In observational research, people who ate chocolate or cocoa regularly were just as likely to experience cognitive decline over five years , although another study reported that they tended to have better cognitive abilities . Small potential benefits of cocoa or cocoa flavanols have also been reported for cardiovascular diseases and diabetes [10-14], which may also affect the risk of cognitive decline and dementia .
There is no rigorous human research on the possible benefits of cocoa or related flavanols for dementia patients. One eight-week clinical trial with 90 people with mild cognitive impairments reported that a flavanol-enriched cocoa drink improved scores on two cognitive tests, lowered insulin resistance, and reduced blood pressure . While these results are promising, further study is needed to confirm whether the benefits will improve quality of life or slow disease progression.
Chocolate, cocoa, and flavanol-enriched cocoa extracts have few known safety issues. There are concerns, however, related to the methylxanthines (caffeine and theobromine), sugars, saturated fat, and additional calories found in most chocolate products. Moderation is essential since chocolate often has very high caloric content, which could contribute to weight gain. Some researchers are exploring whether dark chocolate and cocoa flavanols could protect against obesity , but that research is not conclusive. Flavanol-rich cocoa, chocolate, and supplements are relatively new to the human diet, so little is known about their long-term safety.
NOTE: This is not a comprehensive safety evaluation or complete list of potentially harmful drug interactions. It is important to discuss safety issues with your physician before taking any new supplement or medication.
Clinical studies have used daily doses of flavanol ranging from 520 to 990 mg. Dietary intake of flavanols is much lower, particularly for cocoa-related flavanols. If flavanols are the critical ingredients for possible health benefits, then the chocolate or cocoa commonly found in the diet may not be a good source, depending on ingredients, sourcing, and processing method. Milk chocolate contains less cocoa powder by weight than dark chocolate and, therefore, has a lower flavanol content. "Dutch" processing or alkalization lowers the amount of flavanols by 60 to 90 percent .
Cognitive Vitality blog post, "Cocoa and Chocolate May Treat Cognitive Impairment"
Scientific American article, "Is Cocoa the Brain Drug of the Future?"