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Table 2 Summary characteristics of studies included in the analysis of vitamin D deficiency and risk of dementia

From: Vitamin D deficiency as a risk factor for dementia and Alzheimer’s disease: an updated meta-analysis

 Author& Publication year Study Type Sex Age (Mean) No.Patients (totle) Follow-up duration (year) 25(OH)D (ng/m) OR 95% CI Quality score Vitamin D assessment method Adjustment
 Karakis, 2016, US Prospective cohort W/M 72.4 1663 9 < 10 1.06 0.57–1.98 8 Competitive protein-binding assay and radioimmunoassay Age, gender, smoking, HTN, DM, prevalent CVD, homocysteine, BMI, and vitamin D supplement use.
 Knekt, 2014, Finland Prospective cohort W/M 56.4 5010 17 < 10 1.74 0.64–3.01 8 Radioimmunoassay Age, month of blood drawn, education, marital status, physical activity, smoking status, alcohol consumption, BMI, BP, FPG, serum TG, and serum TC.
 Licher, 2017, Netherlands Prospective cohort W/M 69.2 6087 13.3 < 10
10–20
1.22 1.06 0.97–1.52 0.90–1.26 9 Electrochemiluminescence binding assay Age, sex, season of blood collection, BMI, SBP, DBP, educational level, smoking, alcohol use, calcium serum levels, ethnicity, eGFR, TC, HDL, history of DM, HF, stroke, MI, depressive symptoms, outdoor activity, and APOE-4 carrier status.
 Schneider, 2014, US Prospective cohort W/M 62.0 1652 16.6 < 10 10–20 1.53 1.22 0.84–2.79 0.68–2.19 8 Liquid chromatography-tandem mass spectrometry Age, sex, education, income, physical activity, smoking, alcohol use, BMI, WC, and vitamin D supplementation.
 Feart,2017, France Prospective cohort W/M 73.3 916 11.4 < 10 ng/ml 10–20 2.96 1.43–6.11 8 One-step immunoassay Gender, education, income,
       ng/ml 2.29 1.14–4.58    depressive symptomatology, number of drugs per day, apolipoprotein E e4 allele, BMI, practice of physical exercise, DM, history of CVD and stroke, HTN, hypercholesterolemia, hypertriglyceridemia, smoking status, and Mediterranean diet score
 Olsson, 2017, Sweden Prospective Cohort M 71.0 1182 12 < 10 10–20 1.22 1.06 0.97–1.52 0.90–1.26 8 HPLC atmospheric pressure chemical ionization-mass spectrometry Age, season of blood collection, BMI, education, physical activity, smoking, DM, HTN, hypercholesterolemia, use of vitamin D supplements, and alcohol intake.
 Littlejohns, 2014,US Prospective Cohort W/M 73.6 1615 5.6 < 10 10–20 2.25 1.53 1.23–4.13 1.06–2.21 9 Liquid chromatography tandemmass spectrometry (LC-MS) Age, season of vitamin D collection, education, sex, BMI, smoking, alcohol consumption, and depressive symptoms
 Annweiler, 2011, France Cross-sectional W/M 86.0 288 Not report < 10 2.57 1.05–6.27 7 Radioimmunoassay (DiaSorin, Inc.,Stillwat er, MN,USA) on fastingblood sample Fully adjusted but without detailed information
 Nagel, 2015, Germany Cross-sectional M/W 75.6 1373 Not report < 20 1.08 1.06–2.21 8 ELISA(ImmunodiagnosticSystems Inc., Fountain Hills, AZ,USA) Adjusted for age, sex, school education, smoking status, season, alcohol consumption, BMI, and history of depression
 Buell, 2010, USA Cross-sectional M/W 73.5 318 Not report < 20 2.21 1.13–4.32 7 Radioimmunoassay (DiaSorin, Inc., Stillwater, MN,USA) on fasting blood sample Age, race, sex, body mass index, and education, kidney function, multivitamin use, season, diabetes, hypertension, plasma homocysteine, and ApoE allele status
 Nourhashemi,2018,French Cross –sectional M/W 76.2 1680 Not report < 20 1.038 0.421–2.557 9 a commercially available electro-chemiluminescencecompetitive binding assay gender, BMI, season of blood collection, educational level, and ApoE ε4 genotype