Table 1b:

Diabetes (Case-control studies)

Author (Year)	Source population	Country	Sample size	Definition of Diabetes & PD, covariates	Results	Adjusted variables	Remarks
Skeie et al. 201370	Norwegian ParkWest Study from western and southern Norway	Norway	212 PD patients	PD: Incident PD cases, identified through neurology departments according to Gelb criteria162 DM: Medical and drug history by self-report, referral letters, medical records from hospital and GPs, medical examination	OR 1.94 (95% CI 0.82–4.57)	Not stated
Savica et al. 201243	Records-linkage system of the Rochester Epidemiology Project All residents from Olmsted County	USA	196 PD patients	PD: Incident PD cases, 2 of four cardinal signs, no other cause and responsive to L-Dopa (validated approach) DM: Review of medical records (physician’s diagnosis or use of antidiabetic drugs)	OR 0.67 (95% CI 0.31–1.48)	Age, sex, smoking, coffee consumption	No recall bias possible since diagnoses of comorbidities were documented before the onset of PD
Schernhammer et al. 2011163	Nationwide hospital records (Danish Hospital Register)	Denmark	1’931 PD patients	PD: Hospitalization or outpatient visit for PD plus ≥1 antiPD medication DM: Had to be present at least 2 ys before PD Diagnosis recorded in the Danish Hospital Register Prescription for antidiabetic medication recorded in the Danish Prescription Database	Exposure: DM diagnosis: OR 1.36 (95% CI 1.08–1.71) OR 1.50 (95% CI 1.02–2.22) women OR 1.29 (95% CI 0.97–1.72) men Onset of PD <60 y: OR 2.68 (95% CI 1.04–6.91) Exposure: antidiabetic drug use >2ys prior to PD diagnosis: OR 1.35 (95% CI 1.10–1.65) Onset of PD <60 y: OR 3.07 (95% CI 1.65–5.70)	Age, sex	Exclusion of PD patients with diagnosis of Alzheimer <2 y before PD and with prescription of PD inducing medication 180 days prior to PD: similar results
Miyake et al. 201044	PD cases and controls recruited from hospitals in two regions	Japan	249 PD patients	PD: Cases included within 6 y of onset of PD, diagnosed by neurologists according to the UK PD Society Brain Bank clinical diagnostic criteria DM: Based on antidiabetic drug treatment (information from questionnaires)	OR 0.38 (95% CI 0.17–0.79) Women: OR 0.39 (95% CI 0.11–1.20) Men: OR 0.34 (95% CI 0.11–0.91)	Age, sex, region of residence, smoking, education, physical activity, BMI, alcohol/coffee consumption, dietary glycemic index
D’Amelio et al. 2009164	Outpatients consecutively recruited at the Neurological Department	Italy	318 PD patients	PD: 2 of four cardinal signs, exclusion criteria: 2nd-ary causes of parkinsonism, DIP 180 days prior to PD Dx, or cognitive decline within one yr after PD Dx DM: Self-report (questionnaire) validated by review of medical records (80% valid), plus antidiabetic drug use	OR 0.4 (95% CI 0.2–0.8)	Age, sex, BMI, smoking, alcohol/coffee consumption, years of education
Becker et al. 2008165	Primary care database representative of UK population	UK	3’637 PD patients	PD: Dx recorded by GP plus ≥2 Rx for anti-PD drugs, no drugs inducing parkinsonism 6 months prior to PD Dx DM: Dx recorded by GP	OR 0.95 (95% CI 0.80–1.14)	Age, sex, smoking, BMI, diabetes, Asthma/COPD, ischemic heart disease, heart failure, stroke, arrhythmia, hyperlipidemia, epilepsy, affective and neurotic disorders, schizophrenia, dementia
Scigliano et al. 200647	Hospitalized patients to neurology department	Italy	178 PD patients	PD: Bradykinesia plus tremor, rigidity, or postural instability + good response to L-Dopa 58% with PD duration ≤1yr 30% 1–4ys, 12% ≥4ys DM: Patients with antidiabetic medication in medical records	OR 0.30 (95% CI 0.13–0.72)	Age, sex	Exclusion of patients with atypical parkinsonism and with DIP Control from the hospitalized population potentially more unwell than the general population
Powers et al. 200646	From neurology and general practice clinics of the Group Health Cooperative HMO	USA	362 PD patients	PD: Incident cases, diagnosed by neurologist or GP (2 of 4 cardinal signs), no drugs causing PD within 12 months prior to PD Dx DM: Questionnaire + chart review	Men: OR 0.52 (95% CI 0.28–0.97) Women: OR 0.80 (95% CI 0.35–1.83)	Age, sex, ethnicity, smoking, education
Ho et al. 198951	Individuals living at homes for the elderly	HongKong	35 PD patients (not necessarily incident cases)	PD: Clinical examination by 3 examiners plus assessment at geriatric clinic, positive response to L-Dopa Exclusion criteria: history of cerebrovascular disease, DIP DM: Self-reported	OR 1.6 (95% CI 0.5–5.1)	Age, sex	Very low number of included/exposed cases (6 patients with DM)

BMI = Body mass index; CI = Confidence interval; COPD = Chronic obstructive pulmonary disease; DIP = Drug induced parkinsonism; DM = Diabetes mellitus; Dx = Diagnosis, GP = General Practitioner; HMO = Health maintenance organization; OR = Odds ratio; PD = Parkinson disease; Rx = Prescription; UK = United Kingdom; yr/ys = year(s)