Frequent nightmares are a precursor to Parkinson's disease.

Scientists came to such conclusions during a long-term study involving almost four thousand men over 67 years old. None of the volunteers had Parkinson's disease at the start of the observation. Seven years later, 91 people were diagnosed with it. Most in the first five years. Those who had frequent nightmares were three times more likely to develop Parkinson's within five years than the rest.