Professional occupation and the risk of Parkinson's disease

This research article investigates the link between occupation and risk of PD... it is not just another paper linking farming to Parkinson's (although I find that link interesting too)... instead it uses a classification model called RIASEC which divides occupations according to personality characteristics. 
This topic has always fascinated me... in part because it plays out in clinical practice and is apparent in the patients one sees in clinic... and in part because if dopaminergic deficit influences choice of occupation, then susceptibility really does begin decades before one gets the diagnosis.
Some of the former observation may be down to selection bias... after all the patients I saw in 5 years at Queen Square generally represent a different demographic to that of patients I see at the Royal London... but my overall clinical impression is still consistent with what the authors observe here.
The link between farming and Parkinson's has always been put down to cumulative  pesticide (or other similar toxin) exposure... but in this paper these are very broad occupational categories seemingly driven by personality traits. The authors attempt to explain the association by the notion that higher dopaminergic activity is associated with creative behaviour (and perhaps occupation) and also offers relative protection against Parkinson's. They present alternative possibilities that relate to smoking (and other substance abuse) potentially being protective against Parkinson's and more common in creative occupations OR that creative occupations generate higher dopaminergic reserve which in turn acts as a buffer against neurodegeneration. 
I would like to propose an alternative possibility... and that is circadian clock function has both a strong influence on our behaviour and also potentially on our choice of occupation, as well as having a strong influence on the regulation of normal cellular processes. 'Morning persons' are more likely to pursue conventional occupations than 'evening persons', who I am willing to bet are more likely to be creative... we have recently shown that a lifetime averaged tendency towards one extreme of chronotype (that is being a 'morning person') is causally linked with PD (preprint here). The role that circadian clock function might have in explaining the fascinating work reported in this paper warrants further exploration...

- Alastair Noyce

Eur J Neurol. 2018 Jul 14. doi: 10.1111/ene.13752. [Epub ahead of print]
Darweesh SKL, Ikram MK, Faber MJ, de Vries NM, Haaxma CA, Hofman A, Koudstaal PJ, Bloem BR, Ikram MA.

https://onlinelibrary.wiley.com/doi/abs/10.1111/ene.13752

BACKGROUND AND PURPOSE: Creativity in Parkinson's disease (PD) is strongly related to dopaminergic activity and medication. We hypothesized that patients with PD, including those who are in the pre-diagnostic phase of PD, are prone to choose highly structured 'conventional' professional occupations and avoid highly creative 'artistic' occupations.

METHODS: At baseline of the population-based Rotterdam Study, we asked 12 147 individuals aged ≥45 years about their latest occupation and categorized occupations according to the RIASEC model. Participants underwent baseline and follow-up (median 11 years) examinations for PD. We determined associations of artistic (versus any other occupation) and conventional (versus any other occupation) occupations with PD. Additionally, we pooled our results with a recently published case-control study (Radboud Study).

RESULTS: At baseline, conventional occupations were common [n = 4356 (36%)], whereas artistic occupations were rare [n = 137 (1%)]. There were 217 patients with PD, including 91 with prevalent PD and 126 with incident PD. The risk of PD varied substantially across occupational categories (chi-square, 14.61; P = 0.01). The penalized odds ratio (OR) of artistic occupations for PD was 0.19 [95% confidence interval (CI), 0.00-1.31; P = 0.11], whereas the OR of conventional occupations for PD was 1.23 (95% CI, 0.95-1.66; P = 0.10). The direction and magnitude of ORs were similar in cross-sectional and longitudinal subsamples. Pooled ORs across the Rotterdam and Radboud Studies were 0.20 (95% CI, 0.08-0.52; P < 0.001) for artistic and 1.23 (95% CI, 0.92-1.67; P = 0.08) for conventional occupations.

CONCLUSIONS: The risk of PD varies substantially by choice of professional occupation. Our findings suggest that dopaminergic degeneration affects choice of occupation, which may start in the pre-diagnostic phase of PD.