Associations of Young Adult Intelligence, Education, Height, and Body Mass Index with Subsequent Risk of Parkinson's Disease and Survival: A Danish Cohort Study

Background: The underlying disease mechanisms of Parkinson's disease (PD) are still unknown and knowledge about risk and prognostic factors is sparse. Objective: To examine the association between intelligence, education, body height, and body mass index (BMI) in young adulthood and risk of PD and subsequent survival. Methods: In total, 656,751 men born 1939-1959 with information from conscription examinations around age 19 years were followed for PD and mortality from 1977-2018 in Danish registries. Cox proportional hazard regression was used to conduct the analyses. Results: During follow-up, 5,264 (0.8%) men were diagnosed with PD. Higher intelligence, education, and body height conferred a higher hazard of PD, independent of age at disease onset. BMI above compared to below the mean (22.8 kg/m(2)) was associated with slightly higher hazard of late-onset PD (>60 years). During follow-up, 2,125 (40.5%) men with PD died, corresponding to a 2.55 (95% confidence interval:2.44-2.66) times higher mortality compared to men without PD. Intelligence was inversely associated with mortality in men with and without PD. Higher education and body height were also inversely associated with mortality in men without PD, whereas the estimates were less pronounced and imprecisely estimated for men with PD. Having an obese BMI was associated with higher mortality in men with PD. Conclusion: Intelligence, education, and body height in young adulthood are positively associated with risk of PD later in life among men. BMI above the mean only confer a higher risk for late-onset PD. For men diagnosed with PD, high intelligence is the only early life indicator associated with better survival, whereas obese BMI predicts poorer survival.

Automated summary

The study found that intelligence, education, and body height in young adulthood are positively associated with the risk of developing Parkinson's disease later in life among men, while being obese may only increase the risk of late-onset PD. For men diagnosed with PD, high intelligence is the only early life indicator associated with better survival.