Another finding that suggests that the asymptomatic phase of the disease is very long

American researchers at the Mayo Clinic at Rochester, Minnesota (US) analyzed the health records of people living at Olmsted from 1976  to 1995.

They found 196 patients with Parkinson’s disease and compared them with 196 subjects without the disease,  matched by age and gender, in terms of their history of constipation.  They found that 36% of the patients had a history of constipation before onset, whereas only 20% of the subjects did.  The difference remained large even after correction for other risk factors, such as smoking and consumption of coffee and when the analysis was restricted to only long-term history of constipation (20 years or more).

Source:  Savica et al Neurology 2009; 73: 1752-1758