These findings, published in the Journal of the American Medical Association Network Open Researchers add to a growing body of evidence that ageing-related or neurodegenerative disease, long thought to originate in the brain, could begin in the gut.
Gastrointestinal problems are known to be common in patients suffering from neurodegenerative disorders, the authors said.
The researchers at the Beth Israel Deaconess Medical Center, US, said that gastrointestinal troubles experienced by patients of Parkinson's disease often appear up to two decades before symptoms such as tremors or stiffness in arms or legs, which interfere with one's movement and are usually the grounds for diagnosis.
They said that digestive issues can involve constipation, drooling, difficulty in swallowing and a delayed emptying of the stomach.
Constipation and difficulty in swallowing were strong risk factors related with a more than doubling of Parkinson's disease risk, the authors said.
One of the possible biological mechanisms underlying these relationships between the gut and risk of Parkinson's disease could be problems in regulating dopamine, a brain chemical known to play a key role in digestion, they said.
The authors also proposed that gastrointestinal conditions could trigger the building up of the protein 'alpha-synuclein', which is how Parkinson's disease presents in the brain.
Future research could help understand these mechanisms better, they added.