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Epidemiological studies have identified links between coffee consumption and a variety of health outcomes. For instance, evidence suggests that drinking five to six cups of coffee a day reduces the risk of developing type 2 diabetes, while drinking three to five cups may reduce the risk of developing Alzheimer’s disease and dementia, compared to drinking none at all. A new study suggests that high caffeinated coffee consumption increases a person’s risk for developing dementia.

The authors of the study drew on data from more 390,000 people enrolled in the UK Biobank study who were tracked over a period of eight to 12 years. Looking at individuals’ neurological diagnoses, the researchers found that while drinking two to four cups of coffee was associated with lower odds of developing dementia compared to drinking no coffee or exclusively decaffeinated coffee, consuming more than six cups of caffeinated coffee per day markedly increased those odds. The greater risk associated with high coffee consumption was present even when researchers statistically accounted for a variety of demographic factors such as water intake, exercise, sleep quality, stress, and body mass index. The effect also held up equally in men and women, as well as across different age groups.

Further interesting observations emerged when the researchers examined brain scans of more than 17,500 of the study’s participants. The scans revealed that participants who drank six or more cups per day exhibited the lowest average brain volumes – an effect that was not seen in those who drank decaffeinated coffee, suggesting that the effects were driven by caffeine.

One of the mechanisms that may drive the harmful effects of caffeine on the brain is caffeine’s blockade of the brain’s adenosine A2 receptors, which have been found to play a crucial role in enabling a subregion of the hippocampus (a structure involved in memory formation) to undergo plasticity and learning. In dampening the A2 receptor signal, caffeine might reduce the formation of new connections and potentially dampen levels of neuronal activity to a point where some connections may be eliminated. Importantly, however, research studies in this field are frequently carried out with young mouse brains, and further research across the entire lifespan is needed.

These findings demonstrate that high caffeine consumption (defined as drinking more than six cups a day) may contribute to brain shrinkage and have a detrimental impact on neurological function. Caffeine consumption also influences sleep quality, which in turn influences brain health. Learn more about how caffeine affects sleep in this clip featuring Dr. Matthew Walker.

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