The enduring global popularity of tea may represent a humiliating cultural defeat for the United States, but ultimately it’s for the best. That’s because tea contains loads of compounds with antioxidant and anti-inflammatory activity and may even benefit gut microbiomes. Now, a new study on the health benefits of the world’s favorite flavored beverage may make my fellow Americans reconsider it.
A team of medical researchers led by medical experts from the Chinese Academy of Medical Sciences followed the health of nearly half a million people between the ages of 30 and 79 enrolled in the China Kadoorie Biobank for a period of roughly nine years. In addition to monitoring their health, the Biobank collected data on the subjects’ tea-drinking habits, including daily number of cups, preferred temperature and type, and even strength. During the study period, the researchers monitored how many members of the cohort developed a range of vascular diseases (cardiovascular disease, cerebrovascular disease, pulmonary heart disease, peripheral artery disease, etc.).
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Overall, the team found habitual tea drinkers had a lower risk of vascular diseases. But drilling into the data they found some surprises. First of all, the type of tea mattered. Across vascular diseases, black tea showed greater risk reductions than green tea. The team chalked up this difference to black tea’s oxidation-derived compounds like theaflavin, which has anti-inflammatory and lipid-regulating properties.
The number of cups of tea the participants drank in a day also mattered. The team found that six to eight cups per day was the sweet spot for lowering vascular disease risk, after that it started rising. Drinking around 20 cups of tea per day had the same effect as drinking none, after that point it increased the risk of vascular disease. According to the team, this effect may be caused by caffeine, which can stress out the circulatory system, swamping any health benefits.
Fascinatingly, the temperature of the tea also seemed to have an effect. Those who enjoyed their tea room temperature or hot saw a reduced risk of vascular disease, but those who opted for scalding hot tea saw their risk increase by 16 percent. Why? The researchers aren’t entirely sure. There’s at least some evidence that drinking hot beverages increases esophageal cancer risk, but it’s unclear how that may translate to a rise in vascular disease.
Of course, the study comes with plenty of caveats. For starters, it relies on self-reported behaviors, which aren’t always accurate (although perhaps more so for daily habits). Second, the measures for cups and temperature were entirely subjective—one person’s scalding hot kettle’s-worth of tea may be another person’s tepid mug-full.
It’s for that reason the researchers can’t definitively recommend six to eight cups of tea per day, despite the risk reductions they found. Or as they concluded, “From a public health perspective, the findings support viewing tea drinking as one component of a broader lifestyle pattern rather than as an isolated preventive intervention.” 
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