Introduction
Parkinson’s disease (PD) is a progressive neurodegenerative disease with
significant negative consequences on health and quality-of-life despite
of pharmacotherapies [1,2]. While its etiology remains largely
unknown, numerous factors have been associated with risk of PD [3].
Statins are indicated for primary and secondary prevention of
atherosclerotic coronary and cerebrovascular events, but it has also
been suggested that due to their pleiotropic effects they could modify
the progression of neurodegenerative diseases [4]. Meta-analyses of
observational studies have reported a lower risk of PD among statin
users [5,6]. However, confounding by indication and healthy user
effect might have affected on findings [7]. Furthermore, the inverse
risk has not been unequivocally demonstrated, as four studies have shown
an increased risk of PD in statin users [8-11]. Based on these
earlier observations, studies in specific populations that can better
account for confounding by indication are needed.
Risk of atherosclerotic events is particularly increased in persons with
diabetes and the 2019 American College of Cardiology and American Heart
Association guidelines recommend at least moderate-intensity statin
therapy for all persons with diabetes aged 40–75 years old [12].
Persons with diabetes may also have an elevated risk of PD [13,14].
Therefore, investigation of PD risk factors in this population is
needed. Yet, there are only few studies on the association of statin use
and risk of PD in persons with diabetes, all three of them reporting
lower risk of PD among statin users than nonusers [8-10]. However,
in these studies even short-term statin exposure was associated with
lower risk [8,10], two of the studies were based on same population
[8,10], and one that was published as a short commentary in response
to Lin et al. [8] compared risk of PD among users of simvastatin and
metformin to metformin only users [9]. We investigated whether
statin use in persons with diabetes is associated with a risk of PD and
whether there is a dose-response relationship.