Drinking too much coffee can give the average Joe the jitters, but scientists say caffeine may have the opposite effect on people with Parkinson's disease.
The Canadian study found that drinking between two and four cups of coffee a day can help control tremors, opening the door to new treatment options for the progressive neurodegenerative condition that affects more than 10,000 Kiwis.
Symptoms can include tremors, stiffness of muscles, depression, disturbance of normal sleep, fatigue and lack of sense of smell.
Parkinson's New Zealand chief executive Deirdre O'Sullivan said she was excited by the research but expressed caution at the small scale of the study.
The effect of caffeine on the healthy human brain was widely known but she had not heard any research into its effects regarding Parkinson's, she said.
Coffee could also lead to negative effects, so she said it was probably not wise for those suffering from the disease to dramatically increase their intake until more research had been done.
The study was one of the first in humans to show that caffeine can help with movement impairment in people who had the disease, said study author Ronald Postuma, of McGill University in Montreal.
Previous studies have found that people who drink caffeine are less likely to develop Parkinson's.
Sixty-one sufferers - whose symptoms included daytime sleepiness and some motor symptoms - were given either a caffeine supplement or placebo pill.
Members of the caffeine group were given 100 milligrams of caffeine twice a day for three weeks, then 200 milligrams twice a day for three weeks, which is the equivalent of between two and four cups of coffee a day.
After six weeks, the half that took the caffeine supplement experienced an improvement in their motor symptoms compared with the placebo group, Dr Postuma said.
"This was due to improvement in speed of movement and a reduction in stiffness."
Caffeine had borderline effects on sleepiness, and did not affect depression or night-time sleep quality in the study participants.
Dr Postuma said larger-scale studies need to be carried out over a longer period to clarify the caffeine-related improvements.
"Caffeine should be explored as a treatment option for Parkinson's disease. It may be useful as a supplement to medication and could therefore help reduce patient dosages."
The study was published yesterday in Neurology, the journal of the American Academy of Neurology.