A review of existing published data has suggested that moderate consumption of tea and coffee may significantly reduce the risk of cognitive disorders, including dementia.
Extensive meta-analysis: This discovery, published in journal Nutrition Reviews, was conducted by a team of researchers from China Medical University, led by Ying Zhu and Chun-Xiang Hu.
The researchers performed an extensive review of existing literature, including a meta-analysis that analyzed data from multiple studies. These studies primarily investigated tea, coffee or caffeine consumption as potential risk factors for cognitive disorders, which included dementia, Alzheimer's disease and cognitive impairment without dementia.
The analysis' findings: The meta-analysis encompassed 33 studies, including 22 cohort studies and 11 case-control studies, involving a total of 389,505 participants, of which 18,459 had experienced cognitive disorders. The results showed that coffee consumption was associated with a 27% lower risk of cognitive disorders, while tea consumption was linked to a 32% reduced risk.
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The study suggests that caffeine, a key component of both tea and coffee, plays a pivotal role in enhancing brain function and safeguarding against long-term cognitive issues. Caffeine works by blocking specific receptors, particularly the adenosine receptors, which tend to become overly active. This blockade enhances memory and learning by making significant improvements in signaling and communication in select brain regions.
Optimal consumption levels: The study revealed a nonlinear relationship for coffee, with the strongest protective effect observed at approximately 2.5 cups per day. Beyond this point, there was no significant increase in protection against cognitive disorders. Coffee did not influence the risk of cognitive impairment without dementia.
The relationship between tea consumption and cognitive disorders was linear. The risk of cognitive disorders decreased by 11% for those who consumed just one cup of tea per day. This suggests that even a modest daily intake of tea can offer substantial protection against cognitive decline.
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Ethnic and gender differences: The study also explored variations in the effects of coffee and tea consumption based on ethnicity and gender. Coffee consumption was found to be associated with a decreased risk of cognitive disorders in white individuals, while tea consumption offered more protection to Asian individuals. The protective effects of coffee and tea were also found to be stronger for men than for women.
Questions and limitations: Despite the researchers' best efforts to control for potential variables that could influence the results, there remains a possibility that unmeasured factors, such as tobacco and alcohol consumption or socio-economic factors, might have played a role. Further investigations will be required to validate the role of tea, coffee and caffeine in preventing cognitive disorders.
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