Research is exciting!
It’s also generally very slow. Although the incredibly fast development of the COVID-19 vaccination may lead us to believe that science moves quickly—and it certainly did in this case—the usual course is far more plodding.
Take the studies into how and/or whether drinking tea produces tangible and measurable health benefits. This sort of study often takes place over decades! And results need to be verified, replicated, themselves studied. It’s a laborious process.
A couple years ago, when I looked at whether drinking green tea protects against heart attack and stroke (see Tea: A Magic Elixir?), I concluded that green tea didn’t necessarily protect against either one. A recently published study by M. Teramoto and colleagues (2021) validates that conclusion, showing little evidence that drinking green tea prevents stroke or heart attacks.
However, they did find that drinking green tea improved the prognosis and functional recovery of stroke and heart attack survivors, which builds on an earlier finding by K. J. Mukamal et al. (2002) that drinking tea (black and/or green) improved prognosis after heart attack.
Note the lapse of nearly two decades between these two studies that came to similar conclusions. This sort of research takes time.
There have been many studies on whether tea (black, oolong, and green), coffee, and/or caffeine help prevent cardiovascular disease and/or lower the death rate from cardiovascular disease.
A 2011 study (Mineharu et al.) followed 76,979 people and concluded that drinking tea (green and oolong in this case) did lower a person’s risk of dying from cardiovascular disease. However, since I can access only the abstract for this particular study, I can’t tell whether tea drinking helped prevent disease (which would be at odds with the studies noted above), or whether it improved the prognosis for survivors of stroke and heart attacks. Or whether it didn’t distinguish between the two.
In Teramoto et al.’s study (2021), which followed subjects for over 18 years, researchers found that:
- people who survived a stroke and drank at least 700 ml (23.7 oz) of green tea daily had an approximately 60% lower risk of all-cause mortality (dying from any cause during the study time)
- there was no change in risk of all-cause mortality for people who drank at least 700 ml (23.7 oz) of green tea daily but had not had a stroke or heart attack
Of course, self-reported observational studies such as these have their limits, including the fact that they are self reported. Further, there were only 1,900 people in the 2002 study.
The 2021 study used people in the Japan Collaborative Cohort Study for Evaluation of Cancer Risk database so followed some 46,000, a substantially larger group. Still, some of the cohorts were relatively small. For example, tea drinkers who had had a stroke numbered anywhere from only 62 people (1–5 cups/week) to 140 (3–4 cups/day); these were compared to only 55 non-tea drinkers who had had a stroke.
Future research must also tease out other factors—such as a person’s diet, lifestyle, and overall health before suffering a stroke or heart attack—to figure out how large a role the tea itself plays in the results.
These results, however, continue to build the foundation, guide, and inform future work, especially when there seems to be a fairly strong cause and effect. And I shouldn’t neglect the parallel results that Teramoto et al. found: drinking coffee lowered the risk of all-cause mortality for people who had had neither stroke nor heart attack, as well as for those who had had a heart attack.
The Type of Tea
As tea drinkers, we might be disappointed that the all-cause mortality risk didn’t seem to change for those of us who’ve never had a stroke. Still, there are loads of existing studies that suggest tea lowers the risk of cognitive impairment, depression, psychological distress, osteoporosis, diabetes, liver disease, body pain, and more.
We might also ask this: which type of tea is the most beneficial?
In the studies evaluating tea’s role in heart attack and stroke risk/recovery/prognosis, Teramoto et al. investigated green tea; Mineharu et al. included green, oolong, and black tea; Mukamal et al. lumped together green and black tea. So does the type of tea matter?
One very important point to make is that studies undertaken in Asian countries are likely to focus on green and oolong tea whereas those conducted in western countries are often focused on black tea or a combination of tea types—because that’s what people in those areas generally drink! It’s not really a matter of selecting which tea type to study. Rather, the study evaluates whatever tea the subjects are already drinking.
But no matter what type of tea is being consumed, all forms of them contain various types of polyphenols, those antioxidants that are so beneficial to us.
Polyphenols, Tea’s Acting Agents
In green tea, the majority of polyphenols are epigallocatechin-3-gallate (EGCG), a catechin. When tea is oxidized to produce oolong or black tea, EGCG is converted to more complex forms of polyphenols, such as theaflavins (TF) and thearubigins.
And although many studies of green tea attribute (rightly) its benefits to its catechin EGCG, it’s important to note that the converted form, TF, retains its antioxidant properties. In discussing their research, L.K. Leung and colleagues (2001) concluded that:
this study clearly suggests that the TF present in black tea possess at least the same antioxidant potency as the catechins present in green tea. . . . All data presented here suggest that drinking black tea has benefits equal to those of drinking green tea in terms of their antioxidant capacity.
In their study of tea consumption, W. Shen’s team (2015) affirm the importance of polyphenols in removing free radicals, which serves to protect the nervous system, and they argue that:
the amount of catechins in black tea has been reduced due to [oxidation]. . . . However, catechins converted into theaflavins during [this process] do not reduce their free radical scavenging activity. Thus, black tea and its components have strong antioxidant properties.
Therefore, if you want to drink tea, or think you “should” drink tea, I’d suggest you simply drink whatever tea you prefer (and here I mean true tea, Camellia sinensis, not tisanes).
If you’ve had a stroke or heart attack, I’d suggest you follow your doctor’s advice. But so much of the research into tea and its role in our health, including prognosis, is promising! We just need to remember that conclusive results and recommendations will take further research and time.
Meanwhile, I’m going to go pour another cup of tea. Just in case.
–Leung, L. K., et al., “Theaflavins in black tea and catechins in green tea are equally effective antioxidants,” Journal of Nutrition 131(9):2248–51. 2001.
–Mineharu, Y. et al., “Coffee, green tea, black tea and oolong tea consumption and risk of mortality from cardiovascular disease in Japanese men and women,” Journal of Epidemiology and Community Health 65:230–40. 2011.
–Mukamal, K. J., et al., “Tea consumption and mortality after acute myocardial infarction,” Circulation 105:2476–81. 2002.
–Shen, W., et al., “Tea consumption and cognitive impairment,” PLoS ONE 10(9):e0137781. 2015.
–Teramoto, M., “Green tea and coffee consumption and all-cause mortality among persons with and without stroke or myocardial infarction,” Stroke 52. 2021.