A study from Newcastle University has found that patients with Parkinson's frequently experience urinary urgency, drooling, anxiety and a reduced sense of smell years before motor symptoms appear.
But patients often fail to tell their GP about such issues, despite the effect on their quality of life, researchers said. They urged patients and doctors to discuss such symptoms, because many can be treated.
There are around 127,000 patients with Parkinson's disease in the UK, one in every 500 people.
Around one patient in five first presents with non-motor symptoms and these have the greatest impact on quality of life, the authors said. The symptoms can be treated, but many go unreported and unrecognised by patients and doctors.
In the study, researchers screened 159 patients with recently diagnosed Parkinson's and 99 healthy controls using the Non-Motor Symptom Questionnaire and other tests.
Patients with Parkinson's had 8.4 non-motor symptoms on average, compared with 2.8 among controls.
The most commonly experienced symptoms were excessive saliva and dribbling, urinary urgency, hyposmia, anxiety and constipation, all of which were more common than in the healthy controls.
Researchers were surprised by the high rate of visual hallucinations among Parkinson's patients.
Lead author Tien Khoo PhD, from Newcastle University, said: 'These results show that Parkinson's affects many systems in the body, even in its earliest stages.
'Often these symptoms affect people's quality of life just as much as, if not more than, the movement problems that come with the disease.'
He added: 'Both doctors and patients need to bring these symptoms up and consider available treatments.'