Exercising for less than three hours per week is linked with a slower decline in Parkinson's disease, according to a new study.

Parkinson's is a progressive neurological disease, the symptoms of which include tremors, stiffness and slow movement. An estimated six to seven thousand people in Ireland are affected and there is currently no cure.

Previous research has suggested that physical activity can delay decline in patients, so US researchers decided to investigate this further.

They looked at 3,400 people with Parkinson's over a two-year period and found that those who exercised regularly recorded significantly slower declines in relation to their quality of life and mobility.

"We found that people with Parkinson's disease who maintained exercise 150 minutes (2.5 hours) per week had a smaller decline in quality of life and mobility over two years compared to people who did not exercise or exercised less.

"The smaller decline was significant for people who started the study as regular exercisers, as well as for people who started to exercise 150 minutes per week after their first study-related visit," explained the study's lead investigator, Dr Miriam Rafferty, of Northwestern University and the Rehabilitation Institute of Chicago.

The study did not determine what type of exercise is best for Parkinson's patients, however it did suggest that any type of exercise that is undertaken for at least 150 minutes per week is better than not exercising.

"People with Parkinson's disease should feel empowered to find the type of exercise they enjoy, even those with more advanced symptoms," Dr Rafferty said.

The study also found that when it came to quality of life, the biggest benefits associated with exercising were seen in those with advanced Parkinson's.

The researchers called for exercise and physical activity to be made more accessible to people with severe disabilities, as those with advanced Parkinson's may have poor access to regular exercise.

"The most important part of the study is that it suggests that people who are not currently achieving recommended levels of exercise could start to exercise today to lessen the declines in quality of life and mobility that can occur with this progressive disease," Dr Rafferty added.

Details of these findings are published in the Journal of Parkinson's Disease.