Both drinks can improve brain function, but in very different ways.

Tea Reduces Depression

Drinking three cups of tea a day lowers the risk of depression by 37%, and the benefit doubles when you go to 6 cups a day. That’s what a team of researchers from China concluded after analyzing 11 studies involving nearly 23,000 people. The results apply to green and black teas, but not to herbal teas that lack true tea leaves from the Camellia sinensis plant. Green tea appears to be the most beneficial, and this variety may have preventative effects against dementia as well.

The benefits don’t appear due to caffeine, but may be explained by several ingredients in tea that have positive brain effects: catechins, flavonoids, polyphenols, and theanine.

Hope for Coffee

Where does this leave the coffee drinker? The news there is also good, in moderation. A group of Italian researchers pulled together data from 12 studies involving nearly 340,000 people. They concluded that coffee had protective effects against depression, but only up to a max of 1.75 metric cups a day (about 1 mug). Those benefits plateaued after that first mug, and drinking more than 2.5 metric cups a day (about 2 mugs) slightly increased the risk of depression.

The Italian group also looked at caffeine consumption, regardless of the source. They found that small amounts of caffeine reduced the risk of depression, though that benefit could be due to the forms it came in (e.g. coffee and tea). Drinking more than 300mg of caffeine a day had the opposite effect; it actually raised the risk of depression.

These two studies illustrate the difference between a J-shaped curve and a linear curve. In the case of tea, the risk of depression improves linearly with each up, so that you don’t have to worry about how much you drink (at least within the range of 1-6 cups a day):

For coffee and caffeine, the results show a more frustrating J-shaped curve, where a little is good but too much causes harm:

Moderating Caffeine

The odds for depression rise sharply after 300mg of caffeine. Let’s look at how that safe upper limit translates to in daily metric cups for different beverages (“cups” refers the measuring cups used in baking).

Beverage Max metric cups/day
Brewed Coffee 2
Latte or mocha 2.5
Espresso 0.5
Instant Coffee 5
Brewed black tea 6
Brewed green tea 10
Bottled tea 8
Cola 6
Energy drink 1.5
Energy shot 0.3
(calculations based on caffeine contents gathered by the Mayo Clinic)

Drinking any caffeine after 2pm can worsen mood by disrupting sleep, but the brain benefits of tea hold up even with decaffeinated options.

Other Health Benefits

This data comes from associational studies, which means that cause and effect cannot be concluded despite the large number of people studied. Research from animal studies suggest the brain benefits described here may be real, and we know that coffee and tea have physical health benefits as well. Both lower the risks of diabetes, dementia, cancer, liver problems, and cardiovascular disease.

Sweeteners, whether in the form of sugar, honey, or artificial sugars, can reverse those health benefits. Xylitol, a plant-based sweetener, appears to be one of the healthier options.

When it comes to physical health, coffee may also be a two-edged sword, while tea is a safer route. The higher caffeine content of coffee can worsen some heart conditions, and eve decaffeinated coffee contains acids that can worsen heartburn. In contrast, “There doesn’t seem to be a downside to tea,” concluded the American Dietetic Association spokeswoman Katherine Tallmadge, MA, RD, LD.