Elderly adults who regularly drink green tea may stay more agile and independent than their peers over time, according to a Japanese study that covered thousands of people.

Green tea contains antioxidant chemicals that may help ward off the cell damage that can lead to disease. Researchers have been studying green tea's effect on everything from cholesterol to the risk of certain cancers, with mixed results so far.

For the new study, published in the American Journal of Clinical Nutrition, researchers decided to examine the question of whether green tea drinkers have a lower risk of frailty and disability as they grow older.

Yasutake Tomata of the Tohoku University Graduate School of Medicine and his colleagues followed nearly 14,000 adults aged 65 or older for three years.

They found those who drank the most green tea were the least likely to develop "functional disability", or problems with daily activities or basic needs, such as dressing or bathing.

Specifically, almost 13 percent of adults who drank less than a cup of green tea per day became functionally disabled, compared with just over 7 percent of people who drank at least five cups a day.

"Green tea consumption is significantly associated with a lower risk of incident functional disability, even after adjustment for possible confounding factors," Tomata and his colleagues wrote.

The study did not prove that green tea alone kept people spry as they grew older.

Green-tea lovers generally had healthier diets, including more fish, vegetables and fruit, as well as more education, lower smoking rates, fewer heart attacks and strokes, and greater mental sharpness.

They also tended to be more socially active and have more friends and family to rely on.

But even with those factors accounted for, green tea itself was tied to a lower disability risk, the researchers said.

People who drank at least five cups a day were one-third less likely to develop disabilities than those who had less than a cup per day. Those people who averaged three or four cups a day had a 25 percent lower risk.

Although it's not clear how green tea might offer a buffer against disability, Tomata's team did note that one recent study found green tea extracts seem to boost leg muscle strength in older women.

While green tea and its extracts are considered safe in small amounts, they do contain caffeine and small amounts of vitamin K, which means it could interfere with drugs that prevent blood clotting.