Diabetes and risk of Parkinson's disease: an updated meta-analysis of case-control studies.
BACKGROUND
Whether diabetes increases the risk of Parkinson's disease (PD) is still inconclusive. The objective of this updated meta-analysis is to synthesize evidence from case-control studies that evaluated the association between diabetes and the risk of PD.


METHODS
Seven databases were searched to identify case-control studies that evaluated the association between diabetes and PD. The methodological quality of included studies was assessed using Newcastle-Ottawa scale. All data were analyzed using Review Manager 5.1 software. Subgroup analyses were also adopted, according to stratification on gender, geographic location, source of the control group, smoking, anti-diabetes drug prescription and duration of DM.


RESULTS
Fourteen studies fulfilled inclusion criteria for meta-analysis, yielding a total of 21395 PD patients and 84579 control subjects. Individuals with diabetes were found to have a negative association with future PD (OR 0.75; 95% CI 0.58-0.98) in spite of significant heterogeneity. In subgroup analyses, the negative correlation was still found in studies from North America, non-PD control groups from general population, never smoking individuals, and DM ascertainment based on questionnaire or self-report. Stratification of gender and DM duration showed no significant association. No association was also found in European and Asian individuals, hospital-based controls, ever smoking subjects, DM assessment by medical record or physician diagnosis, and insulin prescription for DM.


CONCLUSIONS
Evidence from case-control studies suggested that diabetic individuals may have a decreased incidence of PD despite significant heterogeneity. More researches are warranted to clarify an understanding of the association between diabetes and risk of PD.
Department of Neurology, the Second Affiliated Hospital of Wenzhou Medical University, Wenzhou, China.
Lin
L
Lu
Department of Neurology, the Second Affiliated Hospital of Wenzhou Medical University, Wenzhou, China.
Deng-Lei
DL
Fu
Department of Neurology, the Second Affiliated Hospital of Wenzhou Medical University, Wenzhou, China.
Hui-Qin
HQ
Li
Department of Neurology, the Second Affiliated Hospital of Wenzhou Medical University, Wenzhou, China.
Ai-Ju
AJ
Liu
Department of Neurology, the Second Affiliated Hospital of Wenzhou Medical University, Wenzhou, China.
Ji-Huang
JH
Li
Department of Neurology, the Second Affiliated Hospital of Wenzhou Medical University, Wenzhou, China.
Guo-Qing
GQ
Zheng
D000368:Aged; D016022:Case-Control Studies; D048909:Diabetes Complications / Q000150:complications*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D010300:Parkinson Disease / Q000209:etiology*; D017594:Publication Bias; D012307:Risk Factors