There's a reason so many people like to relax with a cup of tea – new research finds that green tea may actually help you beat the blahs.

A promising study out of Japan finds that seniors who drink green tea have a much lower risk of depression.

The study, published in the American Journal of Clinical Nutrition, followed more than 1,000 healthy adults over the age of 70. The seniors who drank four or more cups of green tea per day were 44 percent less likely to have symptoms of depression than those who drank one cup or less.

Researchers believe the key is theanine, a calming amino acid present in tea. It may also be why green tea doesn't leave you as wired as other caffeinated beverages – the theanine essentially cancels out some of the effects of caffeine.

Theanine has also been linked to improved immune system function. And while most teas have some theanine, green tea can have up to five times as much.

The new research is consistent with previous studies, which have found that green tea can cut psychological stress. Again, you can probably thank the theanine for that.

Few drinks have been linked to as many health benefits as green tea. In fact, studies have found a connection between this terrific elixir and weight loss, a lower risk for some cancers, and even increased longevity.

No wonder it's so popular in Japan, where people live longer than anywhere else on Earth. Drink up, and maybe you'll live longer too.

PS: Research has also shown that the best way to awaken the polyphenols in green tea is by drinking it with a little lemon and a little sugar. In fact, that combination may even triple the power of your tea. For more on tea's great benefits and how to drink it, read "Just a spoonful of sugar... and a slice of lemon."