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Table 1 Summary characteristics of studies included in the analysis of vitamin D deficiency and risk of AD

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

 Author, Publication year& country Study Type Sex Age (Mean) No.Patients (totle) Follow-up duration (year) 25(OH)D (ng/ml) OR 95% CI Quality score Vitamin D assessment method Adjustment
 Karakis, 2016, US Prospective cohort W/M 72.4 1663 9 < 10 0.97 0.47–2.00 8 Competitive protein-binding assay and radioimmunoassay Age, gender, smoking, HTN, DM, prevalent CVD, homocysteine, BMI, and vitamin D supplement use.
 Afzal, 2014, Denmark Prospective cohort W/M 58.0 4087 21 < 10 10–20 1.25 1.12 0.95–1.64 0.90–1.40 9 Not report Age, sex, month of blood sample, smoking status, body mass index, leisure time and work-related physical activity, alcohol consumption, income level, education, baseline diabetes mellitus, hypertension, cholesterol, high-density lipoprotein cholesterol, and creatinine
 Littlejohns 2014, US Prospective Cohort W/M 73.6 1547 5.6 < 10 10–20 2.22 1.69 1.02–4.83 1.06–2.69 8 Liquid chromatography tandemmass spectrometry (LC-MS) Age, season of vitamin D collection, education, sex, BMI, smoking, alcohol consumption, and depressive symptoms
 Feart, 2017, France Prospective cohort W/M 73.3 916 11.4 < 10 10–20 2.21 1.65 1.28–3.80 0.98–2.77 8 One-step immunoassay Gender, education, income, 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
 Buell, 2010, US Cross-sectional W/M 73.5 318   < 20 2.65 0.99–7.16 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
 Licher, 2017, Netherlands Prospective cohort W/M 69.2 6087 13.3 < 20 1.10 1.00–1.19 9 Electrochemilumin-escence 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.