“Tea... is a religion of the art of life.” Okakura Kakuzō
The history of tea is fascinating and mysterious from the early times in Imperial China to its present role at the heart of British life. The great debate about whether drinking tea is good or bad for our health began in the eighteen century when Catherine of Braganza established tea as a fashionable drink among wealthy classes in Britain.
Fast forward to our times and we see that a fairly large number of systematic reviews and meta-analyses have looked at associations between tea and health.
Let’s begin with cardiovascular disease. Recently published results from eleven trials that included 821 patients were looking at how drinking black and green tea may be associated with a reduction in cardiovascular risk factors. Both teas were found to lower LDL cholesterol level on an average of 0.5 mmol/L, systolic blood pressure by 2.3 mmHg, and diastolic blood pressure by 2.8 mmHg. These results, however, focused on risk factors, not on outcomes, so they need to be interpreted with caution.
A more recent meta-analysis was looking at the results of 22 global studies carried out on more than 850,000 people and found that drinking an additional three cups of tea a day was associated with a 27% lower risk of coronary heart disease, 26% lower risk of cardiac death, 18% lower risk of stroke and 24% decreased mortality.
Tea seems also to be associated with a lower risk of stroke. People who drank at least three cups a day had a 21% lower risk of stroke than those who had only a few cups a week.
One of the largest cross-sectional studies that included more 800,000 participants looking at the association between tea and liver disease. Scientists have proven that people who drank tea were less likely to have liver problems like cancer, liver steatosis, liver cirrhosis and chronic liver disease. This confirmed the data published in 2008
A meta-analysis of eleven studies with almost 23,000 participants published a few months ago concluded that drinking three cups of tea a day is associated with a reduced relative risk of depression by 37%.
A large meta-analysis of 15 studies published last year enrolled more than 545,000 participants looking at how drinking tea may be linked to type 2 diabetes. It turned out that for each additional two cups of tea a day, the risk of developing diabetes dropped by 4.6%. This study was also looking at the benefits of green tea concluding that drinking one cup of green tea a day lowers the relative risk of type 2 diabetes by 11%.
When it comes to green tea, the data is not very consistent. Although a large meta-analysis published in 2011 has shown that green tea was associated with lower rates of prostate cancer, these founding was not confirmed in future studies. A Cochrane systematic review examined all studies available to date, looking at the association between green tea and the risk of cancer and mortality. Scientists examined 51 studies with more than 1.6 million participants. In the end, the results were conflicting, and the evidence wasn’t sufficient enough to give any concrete recommendation.
Take home message
Although large meta-analyses about drinking tea are available, most of the data comes from observational studies, rather than randomised trials. These studies can only prove association, not causation and in reality controlled trials often show different results.
Tea being rich in antioxidants, catechins, proteins, carbs and sodium seem to have plenty of potential benefits. Not mentioning the soothing, comforting and relaxing qualities that are unequivocally beneficial to both our emotional and physical health.