Oct. 13 (HealthDay News) -- A new look at some old data adds convincing evidence that high body fluid levels of the antioxidant urate slow the progressive nerve damage of Parkinson's disease.

However, the researchers also warned of the potential danger of putting that information to immediate use.

"The study doesn't prove that urate is slowing down the disease, and we need clinical trials to see if progression is based on levels of urate," explained study senior author Dr. Michael A. Schwarzschild, associate professor of neurology at Harvard Medical School and director of the MassGeneral Institute for Neurodegenerative Diseases. He and his colleagues reported the finding online Oct. 12 in the Archives of Neurology.

A clinical trial assessing the impact of urate on Parkinson's is beginning, funded by the Michael J. Fox Foundation. It is recruiting 90 people with Parkinson's disease at 10 U.S. medical centers to study whether regular intake of inosine, a widely available dietary supplement that is a precursor of urate, slows Parkinson's-related deterioration of nerves. Results are expected to be available in about two years, but more definitive studies will take five years or longer, Schwarzschild said.

Meanwhile, what should people with Parkinson's disease do? "They should be very cautious," Schwarzschild said. "There may be a temptation, but one should be careful because there are clear safety concerns."

The major dangers of overdosing with urate are kidney stones and gout, but there are other possible risks, such as an increased incidence of cardiovascular disease, he said.

"There is a lot of vice associated with it, and because we don't know if the case is proven, it would be bad advice to take such measures," Schwarzschild said.

Another expert agreed. "I would not at this point recommend to any Parkinson's patients that they take inosine as a supplement," said Dr. Ira Shoulson, professor of neurology at the University of Rochester in New York and a member of the research team. "I would not for several reasons, mostly to do with safety but also about whether it is beneficial. These are things we have to sort out in future years."

As for natural sources of urate, they are mostly things that people are told to avoid for other reasons, Schwarzschild said -- fructose, the sugar often blamed for an epidemic of obesity; alcohol; and even smoking. "There is a lot of it in liver, but who wants to eat that much liver?" Shoulson added.

Parkinson's disease is a degenerative neurological illness in which deterioration of brain cells causes steadily worsening symptoms such as trembling and slowed motion. Indications that urate might affect the course of Parkinson's began to emerge from epidemiological studies decades ago, Schwarzschild said. More solid evidence came from a study reported last year, which led the researchers of the new study to look back at a two-decades-old study of 800 people with Parkinson's disease.

"They had donated spinal fluid as well as blood, so we were able to test for urate levels in spinal fluid, which surrounds the brain cells," Schwarzschild said.

Analysis showed that the one-fifth of participants with the highest urate levels had a 36 percent lower risk of disease progression compared to the one-fifth with the lowest levels.

"Urate is actually one of the major antioxidants that circulates in humans," Schwarzschild said. "Brain cell degeneration in Parkinson's, Alzheimer's disease or ALS [amyotrophic lateral sclerosis, Lou Gehrig's disease], is caused by oxidative damage."

But another expert agreed it's too early for dietary or treatment recommendations.

"This finding is very exciting, but not yet ready for applicability to individual patients," said Dr. Melissa Nirenberg, assistant professor of neurology and neuroscience at Weil Cornell Medical College in New York City, who was not involved in the study.

She said that the previous report had not generated many queries about urate from her patients. "This one may generate more buzz, but it is very, very concerning that uric acid is a risk factor for cardiovascular disease and other diseases," she said.

If she were asked about inosine, "I would never recommend it to a patient at this stage because we don't know whether it is cause-and-effect rather than just a relationship and whether the potential benefits outweigh the risks," Nirenberg said.

SOURCES: Michael A. Schwarzschild, M.D., Ph.D, associate professor, neurology, Harvard Medical School, director, MassGeneral Institute for Neurodegenerative Diseases, Boston; Ira Shoulson, M.D., professor, neurology, University of Rochester, N.Y.; Melissa Nirenberg, M.D., Ph.D., assistant professor, neurology and neuroscience, Weil Cornell Medical College in New York City; online Oct. 12, 2009, and December 2009 print edition of Archives of Neurology