Short answer: Maybe. A small 3-month trial found that a high dose of cocoa flavanols improved one memory task. But the largest trial, COSMOS-Mind (2,262 older adults, 3 years), found that a cocoa extract supplement did not improve cognition. Evidence for chocolate itself is preliminary. A small piece of 70%+ dark chocolate is fine as a treat.

Dark chocolate might help the brain a little, but the evidence is preliminary, and the best trial of cocoa flavanols found no benefit for cognition. The trials also used cocoa extracts, not chocolate.

How much dark chocolate to eat

  • A small piece (20-30 g): Choose 70% cacao or higher, if you enjoy it.
  • Minimally processed: Dutch-processed (alkalized) cocoa loses much of its flavanol content.
  • Low in sugar: Sugar-heavy chocolate bars undermine the benefits.
  • Vary brands and keep portions small: This limits lead and cadmium exposure (see below).

What’s in dark chocolate

  • Cacao flavanols: The main compounds of interest, studied mostly for their effects on blood vessels and blood flow.
  • Theobromine: A mild stimulant. Small studies suggest it may add to alertness, with a weaker effect than caffeine.
  • Phenylethylamine (PEA): Present in small amounts. There is no good evidence that the amount in chocolate affects mood.
  • Magnesium: Needed for the connections between nerve cells to adapt and strengthen.
  • Iron and copper: Needed to make chemical messengers and carry oxygen in the brain.

What the trials found

A small trial (Brickman 2014) enrolled 41 healthy adults aged 50-69, and 37 completed it. For three months they drank a high-flavanol (900 mg a day) or low-flavanol (10 mg a day) cocoa drink. The high-flavanol group did better on one pattern-recognition memory task. They also had more blood volume in the dentate gyrus, a part of the hippocampus involved in memory. The flavanols came from a specially made cocoa product, not chocolate.

The much larger COSMOS-Mind trial (Baker 2023) gave 2,262 older adults a cocoa extract supplement (500 mg flavanols a day) or placebo for three years. Cocoa extract had no effect on global cognition, its main outcome. It also did not change the rate of mild cognitive impairment or dementia, although there were few cases (Sachs 2023).

A related trial, COSMOS-Web (Brickman 2023), enrolled 3,562 older adults and missed its main memory outcome. In a secondary analysis, memory improved in people whose usual diet was lower in quality or in flavanols. The COSMOS studies were partly funded by Mars, Inc. For other foods studied for memory, see foods for memory.

Blood flow and mood

Flavanols trigger nitric oxide production, which widens blood vessels, including those supplying the brain. Small short-term studies have found more blood flow in the brain after high-flavanol cocoa. Whether this improves thinking over time is not established.

A 2019 survey of 13,626 US adults (Jackson 2019) found that people who reported eating dark chocolate had lower odds of clinically relevant depressive symptoms. Only 1.4% of participants ate dark chocolate, and this kind of study can’t show that chocolate caused the difference. Our page on diet and depression covers the wider evidence.

Who should be careful

  • Lead and cadmium: A 2024 analysis of 72 US cocoa products (Hands 2024) found that 43% exceeded California’s Prop 65 daily limit for lead per serving, and 35% for cadmium. Organic products were more likely to have higher levels. Small portions and varied brands limit exposure, which matters most in pregnancy and for children.
  • Caffeine: Dark chocolate (70-85% cacao) contains about 20 mg of caffeine per 25 g, or about 80 mg in a 100 g bar. If you are sensitive to caffeine, take care, especially in the evening. More in caffeine and cognition.
  • Theobromine: Generally safe, but very high doses can cause jitteriness or headaches.
  • Sugar: Even dark chocolate contains sugar, so watch your total intake.
  • Migraine: Chocolate is a common migraine trigger for some people.
  • Kidney stones: Dark chocolate contains oxalates, which may be a concern if you are prone to calcium oxalate stones.

Sources

  • Baker, L. D., Manson, J. E., Rapp, S. R., Sesso, H. D., Gaussoin, S. A., Shumaker, S. A., & Espeland, M. A. (2023). Effects of cocoa extract and a multivitamin on cognitive function: A randomized clinical trial. Alzheimer’s & Dementia, 19(4), 1308–1319. doi:10.1002/alz.12767
  • Brickman, A. M., Khan, U. A., Provenzano, F. A., Yeung, L. K., Suzuki, W., Schroeter, H., Wall, M., Sloan, R. P., & Small, S. A. (2014). Enhancing dentate gyrus function with dietary flavanols improves cognition in older adults. Nature Neuroscience, 17(12), 1798–1803. doi:10.1038/nn.3850
  • Brickman, A. M., et al. (2023). Dietary flavanols restore hippocampal-dependent memory in older adults with lower diet quality and lower habitual flavanol consumption. Proceedings of the National Academy of Sciences, 120(23), e2216932120. doi:10.1073/pnas.2216932120
  • Hands, J. M., Anderson, M. L., Cooperman, T., Balsky, J. E., & Frame, L. A. (2024). A multi-year heavy metal analysis of 72 dark chocolate and cocoa products in the USA. Frontiers in Nutrition, 11, 1366231. doi:10.3389/fnut.2024.1366231
  • Jackson, S. E., et al. (2019). Is there a relationship between chocolate consumption and symptoms of depression? A cross-sectional survey of 13,626 US adults. Depression and Anxiety, 36(10), 987–995. doi:10.1002/da.22950
  • Sachs, B. C., et al. (2023). Impact of multivitamin-mineral and cocoa extract on incidence of mild cognitive impairment and dementia: Results from the COcoa Supplement and Multivitamin Outcomes Study for the Mind (COSMOS-Mind). Alzheimer’s & Dementia, 19(11), 4863–4871. doi:10.1002/alz.13078
  • USDA FoodData Central, SR Legacy: Chocolate, dark, 70-85% cacao solids (FDC ID 170273). fdc.nal.usda.gov