Interesting stuff indeed...dose dependent effect and significance differences observed up to two decades prior to diagnosis. To my knowledge this is the first study that has suggested depression precedes PD by this length of time but anxiety has been shown to antedate PD by a similar length of time...
Neurology. 2015 May 20. pii: 10.1212/WNL.0000000000001684. [Epub ahead of print]
Gustafsson H, Nordström A, Nordström P.
OBJECTIVE:
To investigate the long-term risk of Parkinson disease (PD) after depression and evaluate potential confounding by shared susceptibility to the 2 diagnoses.
METHODS:
The nationwide study cohort included 140,688 cases of depression, matched 1:3 using a nested case-control design to evaluate temporal aspects of study parameters (total, n = 562,631). Potential familial coaggregation of the 2 diagnoses was investigated in a subcohort of 540,811 sibling pairs. Associations were investigated using multivariable adjusted statistical models.
RESULTS:
During a median follow-up period of 6.8 (range, 0-26.0) years, 3,260 individuals in the cohort were diagnosed with PD. The multivariable adjusted odds ratio (OR) for PD was 3.2 (95% confidence interval [CI], 2.5-4.1) within the first year of depression, decreasing to 1.5 (95% CI, 1.1-2.0) after 15 to 25 years. Among participants with depression, recurrent hospitalization was an independent risk factor for PD (OR, 1.4; 95% CI, 1.1-1.9 for ≥5 vs 1 hospitalization). In family analyses, siblings' depression was not significantly associated with PD risk in index persons (OR, 1.1; 95% CI, 0.9-1.4).
CONCLUSIONS:
The time-dependent effect, dose-response pattern for recurrent depression, and lack of evidence for coaggregation among siblings all indicate a direct association between depression and subsequent PD. Given that the association was significant for a follow-up period of more than 2 decades, depression may be a very early prodromal symptom of PD, or a causal risk factor.
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