A new study was published in April 2023 in the journal PeerJ performing a meta-analysis of 7 studies that set to determine if there was a significant correlation between drinking tea and a reduced risk of developing dementia and Alzheimer's disease.
Of the 7 studies, 5 were determined to be of high quality, 2 were moderate quality. The studies observed 410,951 individuals, and were published from 2009 and 2022. These studies were prospective cohort studies which observed large numbers of people over a period of time. This type of long-term study looks for possible connections between a behavior, habit, and/or lifestyle and the development of disease, and in this case, the behavior was the drinking of tea and its relationship to the development of dementia and/or Alzheimer's.
The meta-analysis found that there was a reduced relative risk of developing any form of dementia in those individuals who drank tea. There was a relative risk (RR) of 0.71 for all-cause dementia (RR = 0.71, 95% CI [0.57–0.88], I 2 = 79.0%, p < 0.01), which in basic language means there was a 29% reduced relative risk of developing dementia in people who drink tea regularly. There was also an observed enhancement of reduced risk in people "with less physical activity, older age, APOE carriers, and smokers" (Jiang et al., 2023).
To make sense of the statistical notation used, let's get some assistance from ChatGPT to understand this statistical notation:
This statistical notation is common in scientific research, particularly in meta-analyses and epidemiological studies. Let's break down each component:
1. RR = 0.71: This represents the Relative Risk (RR). In your context, RR is equal to 0.71, which means that the group being studied has a 29% reduced risk of the outcome compared to the reference group. This was discussed in a previous response.
2. 95% CI [0.57–0.88]: This indicates the 95% Confidence Interval (CI) for the relative risk. In your case, the confidence interval ranges from 0.57 to 0.88. A confidence interval provides a range of values within which we can be reasonably confident (in this case, 95% confident) that the true relative risk lies. Since the confidence interval does not include the value 1 (the null value for RR), it suggests that the observed RR of 0.71 is statistically significant. In other words, there's evidence to suggest a reduced risk.
3. I² = 79.0%: This represents the I-squared statistic (I²), which measures the degree of heterogeneity among the studies included in the meta-analysis. An I² of 79.0% indicates a high level of heterogeneity among the studies. In meta-analysis, heterogeneity refers to the degree of variation in study results beyond what would be expected by chance. High heterogeneity suggests that the studies may differ substantially from each other in terms of their findings or methodologies.
4. p < 0.01: This is the p-value associated with the meta-analysis results. A p-value is used to determine the statistical significance of the findings. In this case, p < 0.01 means that the observed results are statistically significant at the 0.01 significance level, which is a very stringent threshold. In other words, the findings are highly unlikely to be due to random chance alone.
In summary, the notation you provided indicates that there is a statistically significant reduction in the risk of the outcome (RR = 0.71) with a 95% confidence interval of 0.57 to 0.88. However, there is a high degree of heterogeneity among the studies included in the meta-analysis (I² = 79.0%), and the results are highly statistically significant (p < 0.01).
This is very encouraging and hopefully motivating for tea-drinkers or anyone who is looking to find ways to offset their risk of cognitive disease. While there are obviously no direct effects that guarantee any outcome, especially since cognitive disease is complex, not fully understood, and can be caused by many factors, it is still worth enjoying tea as a daily habit as it appears to reduce risk to some degree.
At Abundant Heaven Integrative Acupuncture, we aim to provide a human-centered and evidence-based approach to healthcare that bridges tradition, science, spirit, and practicality. We love tea regardless of its health benefits, but we especially love when we can enjoy something that isn't adding to the burden of disease and suffering. Tea has long been valued for it's stimulating and sensual qualities and Chinese medicine has also valued it for it's therapeutic qualities. With contemporary scientific research, we are able to deepen our appreciation of this wondrous and diverse plant as it seems to protect our nervous systems/brains from premature aging.
If you are already a fan of tea or are just starting to explore the wide world of tea, please check out our selection of hand-selected, high-quality teas, as we are certain you will find something you can enjoy.
Jiang, N., Ma, J., Wang, Q., Xu, Y., & Wei, B. (2023). Tea intake or consumption and the risk of dementia: A meta-analysis of prospective cohort studies. PeerJ, 11, e15688. https://doi.org/10.7717/peerj.15688