Drinking moderate amounts of coffee or tea can decrease the risk of cognitive disorders such as dementia, according to a recent study published in Nutrition Reviews.
Aged-related cognitive disorders such as Alzheimer’s disease place a huge burden upon individuals and the healthcare system. Current therapeutic drugs are limited in their potential to treat these disorders, and thus attention could be shifted towards targeting risk factors that can be managed, including dietary habits.
Coffee and tea have been a part of human diets for centuries, but the effect of caffeine on brain health – especially on the risk of developing cognitive disorders – has been a topic of much debate among researchers, due to inconsistent results between studies.
To provide a more definitive answer, researchers from China Medical University led by Ying Zhu and Chun-Xiang Hu performed an updated review of the literature. This included conducting a meta-analysis, which is in essence a large investigation analyzing many studies at once. For the studies to be deemed of high quality and acceptable to be included in the meta-analysis, the studies were required to meet strict criteria.
For example, the authors focused on case-control studies (comparing people with and without a condition to find potential causes) or cohort studies (following a group of people over time to see who develops the condition being studied). These studies also exclusively investigated tea, coffee or caffeine consumption as potential risk factors for cognitive disorders, which was defined as dementia, Alzheimer’s disease, or cognitive impairment without dementia (CIND).
Two of the researchers independently searched several databases for studies to include in the meta-analysis. In total, 22 cohort studies and 11 case-control studies published across 1990 through to 2019 were selected. This involved 389,505 participants – 18,459 of which included cases of cognitive disorders.
Statistical analyses were then performed across the 33 studies.
Coffee and tea consumption was found to be linked to a lower risk of cognitive disorders, with an overall relative risk of 0.73 and 0.68 respectively. In other words, individuals who drink coffee or tea are about 27% and 32% less likely, respectively, to develop cognitive disorders compared to those who don’t.
The researchers also conducted a dose–response analysis, which investigated whether changing the amount of daily coffee or tea altered the risk of developing cognitive disorders.
A nonlinear relationship was found between coffee consumption and Alzheimer’s disease risk, and the strength of protection offered by coffee peaked at approximately 2.5 cups per day. There was no obvious change to protection with a higher quantity of coffee per day. Coffee also did not influence the risk of developing CIND.
Additionally, a linear relationship was found between tea consumption and cognitive disorders, and the risk of death from cognitive disorders decreased by 11% for those who consumed 1 cup per day.
Deeper analyses were also conducted with a focus on ethnicity and sex. Coffee consumption was associated with decreased risk of cognitive disorders in White individuals, whereas tea consumption was associated with decreased risk of cognitive disorders in Asian individuals. Protection was stronger for men than that for women in both coffee and tea consumption.
Zhu and colleagues concluded that, “many studies have demonstrated that caffeine improv[es] cognitive performance in the short term and prevent[s] cognitive impairment in the long term. The molecular mechanisms of caffeine function via the antagonism of excessively activated adenosine receptors. … blockade of the adenosine receptors as the molecular bases can integrate neurotransmitter signaling, thereby controlling synaptic plasticity in regions relevant to memory and learning.”
In simpler terms, caffeine allows temporarily increased brain function and also protects the brain against long-term cognitive problems. Caffeine works to block certain receptors that become overactive, specifically the adenosine receptors. This improves signaling and communication in certain brain areas, and therefore improves memory and learning.
Some limitations are to be noted. Despite the researchers’ efforts to control for potential variables that could affect the results, there remains a possibility that unmeasured factors may have played a role, such as tobacco and alcohol consumption, or income and educational levels. Further investigations would be required to validate the role of tea, coffee and caffeine in the prevention of cognitive disorders.
The study, “Moderate coffee or tea consumption decreased the risk of cognitive disorders: an updated dose–response meta-analysis”, was authored by Ying Zhu, Chun-Xiang Hu, Xu Liu, Rui-Xia Zhu, and Ben-Qiao Wang.