Risk Factors

Parkinson's disease affects about 3% of Americans over 65 years old. Experts estimate that this percentage could double in the next 30 to 40 years. The symptoms of parkinsonism (tremor, gait disturbance, bradykinesia, and rigidity) occur in even more people, estimated to be 8 million over 65. In a study that included very mild symptoms, parkinsonism occurred in about 15% of people 65 to 74 years of age, about 30% in those 75 to 84, and over half of people older than 85.

Age

The average age of onset of Parkinson's disease is 55. About 10% of Parkinson's cases are in people younger than 40 years old. Older adults are at higher risk for both parkinsonism and Parkinson's disease. There is some evidence, however, that the risk declines significantly after 75 and that the very elderly are at low risk.

Gender

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Some research indicates that men may face up to twice the risk as women. Estrogen may offer some protection for women up until menopause. A 2001 study, for example, reported a higher rate of Parkinson's disease in women who had undergone hysterectomy. One study suggested that the disease also progresses more rapidly in men than women. Older women seem to be more at risk for gait disturbance and men for rigidity and tremor.

Family History of PD

People with siblings or parents who developed Parkinson's at a younger age are at higher risk for Parkinson's disease, but relatives of those who were elderly when they had the disease appear to have an average risk.

Ethnicity

African- and Asian-Americans have a lower risk than European-Americans. Some evidence suggests that non-Caucasians may be more vulnerable to an atypical form of PD, which causes early impairment in thinking and has a poor response to levodopa, the primary PD treatment.

Middle-Age Weight Gain

Increasing fatness in middle age was associated with a higher risk of PD in a 2002 study.