The slow, controlled motions of tai chi can help the impaired balance of people with mild or moderate Parkinson's disease, and the improvements persist for at least three months, according to a small study out Wednesday.

Compared with people who received stretching exercises, tai chi practitioners had fewer falls, longer strides and better balance, researchers found.

"Tai chi fits very well to address the problem Parkinson's disease patients face," said Fuzhong Li of the Oregon Research Institute in Eugene, whose findings appear in the New England Journal of Medicine.

Difficulty walking and remaining standing are hallmarks of Parkinson's, which results from the death of brain cells that generate the chemical dopamine.

"We're not going to get rid of the symptoms. It's not a drug. It can't cure the disease. But, in my view, it can slow down the progression of the disease," Li told Reuters Health.

Although not all studies agree, other research has shown that because it is a balance-based exercise, tai chi may help improve strength and reduce falls in older adults. But there are few large studies in Parkinson's patients.

Li and his colleagues sent 195 seniors, all from Oregon, to one of three classes that met twice weekly for an hour. All could stand unaided, but some needed a device to help them walk.

The tai chi exercises were designed to improve balance with a controlled displacement of the center of mass. Resistance training with ankle weights and weighted vests was used in a second group to strengthen muscles important to posture, balance and gait. A third group had classes that involved gentle stretching.

People in all three groups started off with similar 64-point scores on a 100-point scale that measured how far they could lean or shift their center of gravity without falling.

But after 24 weeks of classes, those in the stretching group saw their average score drop by two points, indicating some deterioration in their condition.

The typical score rose by four points in the resistance group and by 10 points among the tai chi practitioners.

All of the volunteers were tested when their medication was working and their symptoms were controlled.

The improvement with tai chi was even more significant on a test to see how far the person could move toward a target without extraneous movement.

Stride length, walking velocity, knee movement and other measurements also showed more improvement. And people who did tai chi reported only 62 total falls during the training -- less than half of what the other groups reported.

Three months after the classes stopped, some of the benefits persisted. For instance, tai chi practitioners had 60 percent fewer falls than the resistance-training group and 69 percent fewer than the stretching group.

"This is the first time to my knowledge that a study was able to show some durability as a treatment for balance," Li said. "This was a big gap in a research field that didn't have any follow-up data with an exercise regimen."

There was, however, some slippage. The average score for leaning and shifting gravity, which had improved by 10 points in the tai chi practitioners, appeared to drop slightly.

The nice thing about tai chi, he said, is that "this is not equipment-dependent. It can be practiced at any place, at any time."

Parkinson's affects at least 500,000 Americans, most of them elderly, according to the National Institute of Neurological Disorders and Stroke, which funded the new study.

The cost of tai chi classes varies, but prices are typically similar to those of other types of exercise classes.