| Summary: | Objectives: To determine the risk of early onset Parkinson's disease (PD) associated with well water consumption and other risk factors. Design: A case control study with strata matching by age group, gender and current urban or rural residence. Setting: Republic of Ireland, between 1993 to 1995. Participants: Cases with Parkinson's disease, fulfilling at least two of the four cardinal features, with date of birth from 1st January 1926 and disease onset before 56 years. Controls were selected using stratified random sampling from the electoral register. Outcome measures: Odds ratio and 95% confidence interval for well water consumption and other risk factors. Results: Increased risk was associated with well water consumption (odds ratio per 20 years exposure 1.33, 95% CI 1.00 to 1.77), family history of PD (odds ratio 2.15, 95% CI 1.09 to 4.27), and serious head injury (odds ratio 3.08, 95% CI 1.66 to 5.71). Decreased risk was associated with childhood contact with a dog (odds ratio 0.44, 0.25 to 0.78), recall of chicken pox (odds ratio 0.51, 95% CI 0.32 to 0.83), smoking status (odds ratio for 30 or more pack years for smokers 0.19, 95% CI 0.07 to 0.57), exposure to insecticides (odds ratio 0.44, 95% CI 0.25 to 0.77), glue (odds ratio 0.52, 95% CI 0.29 to 0.93), paints (odds ratio 0.37, 95% CI 0.22 to 0.60) and cumulative socioeconomic position (odds ratio for a point reduction in socioeconomic position 0.74, 95% CI 0.61 to 0.90). Conclusions: These results have identified a wide range of exposures from childhood to adulthood that may influence the risk of PD across the life course. Because of potential biases, it is important that these results are replicated in other designs such as occupational or population based cohort studies.
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