Chocolate, Stress, and the Brain: The Cognitive Role of Flavanols

As the season of Advent fills homes with chocolate, a new study adds a scientific twist to this familiar indulgence: the compounds that give dark chocolate its characteristic astringent bite may also sharpen the mind.

Astringency is the dry, puckering sensation you notice when eating dark chocolate, sipping strong black tea, or biting into an unripe banana. It happens because flavanols, plant compounds abundant in cacao, bind to proteins in saliva, reducing lubrication and creating that rough, dry mouthfeel. While often thought of as just a taste or texture, this sensation acts as a mild stress signal, activating pathways in the brain and nervous system that heighten alertness, focus, and memory.

Recent research in Current Research in Food Science (Fujii et al., 2025) reveals that cocoa flavanols can activate the brain’s locus coeruleus noradrenergic system. This network is central in regulating arousal, attention, and memory consolidation. These findings open a new chapter in the science of “neuroactive nutrition,” suggesting that the sensory properties of food themselves - how something feels or tastes - may directly influence brain chemistry and cognition.

Flavanols: More Than Just Antioxidants

Flavanols such as (–)-epicatechin, (+)-catechin, and procyanidins are abundant in cacao, red wine, and certain berries. They have long been studied for their vascular and antioxidant effects, improving endothelial function and supporting cardiovascular health. Yet despite these benefits, flavanols exhibit low bioavailability - the fraction that actually enters the bloodstream after ingestion is small. This raises a key question: how can flavanols influence brain function when so little of them is absorbed? Fujii and colleagues propose that the sensory perception of flavanols, particularly their astringency, may trigger neurophysiological responses through both sensory and gut-brain pathways.

How the Study Was Conducted

The research team administered purified cacao flavanol extracts to adult male mice via oral gavage at doses of 25 or 50 mg per kilogram of body weight, while control mice received only distilled water.

A battery of behavioural and biochemical tests followed:

• Open-field test to measure wakefulness and arousal (this test can also reflect anxiety-like behaviour, but in this study it was primarily used as an index of activity and alertness)

• Novel object recognition to evaluate short-term memory

• Urinary catecholamines to assess activation of the sympathetic nervous system (the branch of the autonomic nervous system responsible for “fight-or-flight” responses)

• Mass spectrometry and gene expression assays to track neurotransmitter activity in the brain

Together, these measures captured both behavioural outcomes and the underlying neurochemical signatures of flavanol exposure.

Activation of the Locus Coeruleus

Within minutes of administration, flavanol-treated mice became more active and alert - travelling longer distances, spending more time in the centre of the arena, and exhibiting more grooming and rearing behaviours, all hallmarks of heightened wakefulness. When tested on memory, they spent significantly more time exploring a novel object, indicating stronger short-term memory formation.

Mass spectrometry showed a surge of noradrenaline (NA) in the locus coeruleus (LC)- a tiny brainstem nucleus that serves as the command centre for the body’s arousal and attention systems. Noradrenaline is a key neurotransmitter that increases alertness, enhances attention, and helps the brain prioritise important stimuli. Elevated NA levels were also observed in the hypothalamus and nucleus accumbens, regions that integrate motivation and emotion. At the molecular level, gene expression analyses revealed an upregulation of tyrosine hydroxylase and dopamine β-hydroxylase - enzymes essential for synthesising NA - within both the LC and the ventral tegmental area (VTA). Together, these findings demonstrate that flavanol ingestion rapidly primes noradrenergic and dopaminergic circuits, suggesting a neural basis for improved attention, vigilance, and memory consolidation.

A “Positive Stress” Response

Biochemical assays revealed that urinary NA and adrenaline increased in a dose-dependent manner, confirming activation of the sympathetic-adrenal-medullary (SAM) axis - the body’s rapid stress-response system. Simultaneously, corticotropin-releasing hormone (CRH) expression increased in the hypothalamus, signalling engagement of the hypothalamic-pituitary-adrenal (HPA) axis. This dual activation represents what the authors termed a “positive stress” response: a short-lived, adaptive state that enhances alertness and cognitive readiness without causing harmful chronic stress. In essence, flavanol exposure may trigger a mild “fight-or-flight” burst of neural energy, temporarily boosting sensory processing, attention, and memory.

The Sensory Hypothesis: Taste as a Neurochemical Signal

Given the extremely low bioavailability of flavanols, the authors suggest that astringency itself - that dry, tightening sensation in the mouth - may act as a neural signal.

Unlike sweetness or bitterness, astringency is not mediated by taste buds but by somatosensory nerves, including the trigeminal and vagal pathways, which detect tactile and chemical stimuli. Flavanol oxidation in the mouth and gut generates reactive oxygen species that activate transient receptor potential (TRP) channels on peripheral sensory neurones. These signals then travel to the brainstem, where they may engage the LC and trigger the noradrenergic cascade observed in the study.

In other words, the feel of chocolate may directly stimulate the brain’s arousal network, transforming a gustatory experience into a neurochemical event.

Implications and Outlook

This research provides a mechanistic link between flavour perception and neurophysiology, supporting the idea that sensory properties of food - not just nutrients - can influence brain function. The findings complement clinical evidence that long-term cocoa flavanol intake enhances hippocampal-dependent memory and cerebral blood flow in older adults (Brickman et al., 2023).

While the doses used in mice exceed typical dietary intake, the study emphasises the concept of sensory nutrition: taste, texture, and aroma can act as physiological stimuli. This principle is not limited to chocolate; other sensory experiences, such as the crunchiness of crisps or the spiciness of chili, have also been shown to engage neural circuits and modulate arousal and attention.

Future research should explore how repeated flavanol exposure affects brain function, mood, and stress adaptation in humans, including potential risks of prolonged sensory-induced stress activation.

A New Way to Think About Chocolate

This study reframes chocolate as more than a comfort food - it may act as a neuromodulator, with flavanols engaging sensory and autonomic pathways to influence cognitive processes. As Advent brings its familiar association with chocolate, this research reminds us that even everyday sensory experiences can engage complex neural circuits. Taste, it turns out, may be one of the more direct routes to the brain.

As this is our last article of the year, from all of us at Women in Neuroscience UK: enjoy the holidays, take some time for yourself, and here’s to another year of sharing insights, supporting our community, and highlighting the voices of women in neuroscience.

References

• Fujii, Y. et al. (2025). Astringent flavanol fires the locus-noradrenergic system, regulating neurobehavior and autonomic nerves. Current Research in Food Science, 11, 101195.

• Brickman, A.M. et al. (2023). Dietary flavanols restore hippocampal-dependent memory in older adults with lower diet quality and lower habitual flavanol consumption. Proc. Natl. Acad. Sci. U.S.A., 120(23), e2216932120.

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This article was written by Neave Smith and edited by Rebecca Pope, with graphics produced by Saba Keshan. If you enjoyed this article, be the first to be notified about new posts by signing up to become a WiNUK member (top right of this page)! Interested in writing for WiNUK yourself? Contact us through the blog page and the editors will be in touch.