Health Benefits of Tea? Here’s What the Evidence Says

Moreover, most of the studies were done in Asia, where things might not be generalizable to the United States in terms of tea drinking. Regardless, the authors felt there was insufficient evidence to give any firm recommendations. A more recent study agrees.

Again, these are all mostly data from observational studies, and as such, they can’t prove causality and should be taken with a grain of salt. We’ve been burned many times before by assuming that what we see in associations in cohort studies will turn out to be truly causal when behavior changes, only to see that fall apart in randomized controlled trials.

The majority of studies have been done in Asian countries where tea drinking is much more common than in the United States. It’s possible that the people who don’t drink tea in those countries are different from those who do in a way that doesn’t translate to people in the United States. Finally, there seems to be less of a dose response than in the studies of coffee: Few of the studies could detect any response with fewer than three cups of tea a day.

There are some randomized studies, however, that don’t have most of these limitations. Green tea has been claimed to help people lose weight. Enough people believe this that 18 randomized controlled trials with 1,945 participants have been reviewed. Half of these trials took place in Japan, and only one in the United States. The evidence found that green tea produced a small weight loss in overweight and obese adults. But the difference was not significant. And green tea also didn’t help with the maintenance of weight loss previously achieved.

Green tea catechins, antioxidants found in the drink, had no effect on HDL cholesterol, triglyceride levels or C-reactive protein concentrations. Two more meta-analyses confirmed these findings.

But 11 trials that included 821 patients found that green tea and black tea can reduce other cardiovascular risk factors. Both were found to reduce low-density lipoprotein an average of 0.5 mmol/L, systolic blood pressure 2.3 mmHg, and diastolic blood pressure 2.8 mmHg. These results should be interpreted with caution, however, as they focus on risk factors and not necessarily outcomes. There were also few studies contributing to each of these findings, so the results may not stand up to further scrutiny or replication.

At the end of all of this, I’m a little less impressed with the body of evidence regarding tea than I was with that of coffee. I admit that this is an interpretation, and others may disagree. The lack of a dose response in many of these trials, coupled with the fact that so many were performed in countries with markedly different tea consumption from our own, makes these results less generalizable than those of coffee were.

But the conclusions I would make are similar. I wouldn’t strongly recommend that anyone take up tea based on these findings. But there seem to be some potential benefits, and there don’t seem to be harms. Drink it if you like it. It, too, seems to be a completely reasonable addition to a healthful diet.

Aaron E. Carroll is a professor of pediatrics at Indiana University School of Medicine. He blogs on health research and policy at The Incidental Economist, and you can follow him on Twitter at @aaronecarroll.