Parkinson's is a degenerative brain disorder that can cause tremors, slowed movements, stiff limbs and gait or balance problems.
Researchers at Montreal's McGill University and investigators in Toronto and Brazil randomly assigned 61 people with Parkinson's disease to take up to 200 milligrams of caffeine or a placebo twice a day for six weeks. The amount of caffeine was the equivalent of between two to four cups of coffee a day.
The study, published in Wednesday's online issue of the journal Neurology, was designed to test whether caffeine helps with the daytime sleepiness often experienced by those who have Parkinson's.
The stimulant didn't seem to help daytime sleepiness. But on average, those in the caffeine group showed a five-point improvement in symptom severity ratings compared with those who weren't taking caffeine.
Checking for caffeine tolerance
Those using caffeine also showed improvements in the speed of their movements and stiffness.
"It is too early to say whether it has any long-lasting effect, but at least caffeine does not need to be avoided," said study author Ronald Postuma, a neuroscientist at the McGill University Health Centre.
"Patients can perhaps use coffee like anybody else, and there may be a short-term additional benefit on their motor symptoms."
Before the study, participants drank about one cup of coffee a day.
The researchers did not find any changes in quality of life, depression or sleep quality.
Adverse events such as gastrointestinal upset were similar for both groups.
The study was short in duration and caffeine's effects may wear off in the long-term if people become tolerant to it, the researchers cautioned.
They called for longer-term trials on a wider variety of Parkinson's patients.
Caffeine seems to block a malfunctioning brain signal in Parkinson's disease, said Dr. Michael Schwarzschild of Massachusetts General Hospital in Boston, who wrote an accompanying journal editorial.
Earlier Parkinson's studies were small and used much higher or lower doses of caffeine, Schwarzschild noted.
"Although current data do not warrant a recommendation of caffeine as a therapeutic intervention in Parkinson's disease, they can reasonably be taken into consideration when discussing dietary caffeine use," Schwarzschild concluded.
The stimulant is safe and inexpensive, but that's actually a drawback for further research, Postuma said.
"Given that it is widely available, no pharmaceutical company will be able to make profits," Postuma said in an email. "This essentially rules them out as funders. So moving forward will rely on government and foundations."
The study was supported by the Canadian Institutes of Health Research and the Webster Foundation.