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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/m2) 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. [ABSTRACT FROM AUTHOR]

Introduction: Cannabis is by far the most widely used and abused drug listed on the Drug Enforcement Administration's Schedule I, which includes drugs with a high potential for abuse. There is evidence of short‐term negative effects of cannabis use on cognition, but only a limited number of studies have explored the association between cannabis use and age‐related cognitive decline. The aim of the present study was to investigate the relationship between cannabis use and age‐related cognitive decline from early adulthood to late midlife. Methods: The study population consisted of 5162 men who had participated in Danish follow‐up studies on cognitive aging. These studies included scores on the military intelligence test Børge Prien's Prøve from both the conscription assessment (mean age = 20 years; p1 and p99: 18 and 26 years) and from the follow‐up (mean age = 64 years; p1 and p99: 55 and 72 years) as well as extensive data on lifestyle and health from the follow‐up questionnaires. The association between cannabis use and age‐related cognitive decline was investigated in linear regression models. Results: Men with a history of cannabis use had less cognitive decline from early adulthood to late midlife compared to men without a history of cannabis use. Among cannabis users, neither age of initiation of cannabis use nor frequent use was significantly associated with a greater age‐related cognitive decline. Discussion and Conclusions: In a sample of more than 5000 men followed for a mean of 44 years, we found no significant harmful effects of cannabis use on age‐related cognitive decline. [ABSTRACT FROM AUTHOR]