Prenatal and early life factors and risk of Parkinson's disease.

Few studies have investigated the relation between early life factors and risk of Parkinson's disease (PD), although a potential role of exposures during pregnancy and childhood has been hypothesized. The study population comprised participants in two prospective cohorts: the Nurses' Health Study (121,701 female nurses followed up from 1976-2002) and the Health Professionals Follow-up Study (51,529 male health professionals followed up from 1986-2002). PD risk was examined in relation to season of birth, birthweight, parental age at birth, preterm birth, multiple birth, ever having been breast-fed, and handedness. We identified 659 incident PD cases. No significant relation with PD was observed for birthweight, paternal age, preterm birth, multiple birth, and having been breast-fed. A modest nonsignificant association was suggested for season of birth (30% higher risk of PD associated with spring versus winter birth) and for older maternal age at birth (75% increased risk among those with mothers aged 30 years and older versus younger than 20 years). Left-handedness was associated with a 62% increased risk of PD in women but not in men. Further investigation of the relation between prenatal, perinatal, or neonatal factors and PD in other study populations is suggested.