Table 1.
Characteristics of the 19 studies included in this meta-analysis
| Study | Study design | Sample size | Age (year, mean or median) | Male (%) | Country/Race | Control setting | Outcome of interest | ||||
|---|---|---|---|---|---|---|---|---|---|---|---|
| Total | AA | Control | AA | Control | AA | Control | |||||
| Marahatta S, 2019 | Case-control study | 60 | 30 | 30 | 28.37+10.070 | 30.50 + 9.032 | 16 (51.6%) | 15 (48.4%) | Nepal | Age- and sex-matched healthy controls from hospital staffs | Vitamin D level, Vitamin D deficiency |
| Rehman F, 2019 | Case-control study | 270 | 135 | 135 | 26 ± 12.89 | 26 ± 13.20 | 91 (67.41%) | 91 (67.41%) | India | Age- and sex-matched healthy controls | Vitamin D level, Vitamin D deficiency, serum calcium level |
| Siddappa H, 2019 | Case-control study | 200 | 100 | 100 | 24.52 ± 10.06 | 28.96±11.49 | 72 (72%) | 58 (58%) | India | Age- and sex-matched healthy controls without any history of alopecia areata or other autoimmune/systemic diseases | Vitamin D level, Vitamin D deficiency |
| Daroach M, 2018 | Case-control study | 60 | 30 | 30 | 28.9 ± 9.96 | 31.17 ± 9.43 | 11 (36.67%) | 16 (53.33%) | India | Age- and sex-matched healthy controls | Vitamin D level, Vitamin D deficiency |
| Gade V.K.V., 2018 | Case-control study | 90 | 45 | 45 | 32.73 ± 10.43 | 33.98 ± 8.48 | 14 (31.1%) | 14 (31.1%) | India | Age- and sex-matched healthy volunteers | Vitamin D level, serum calcium level |
| Unal M, 2018 | Case-control study | 54 | 20 | 34 | 12.4 ± 4.2 | 16.6 ± 0.8 | 14 (70%) | 15 (44.12%) | Turkey | Pediatric healthy controls recruited from individuals who visited to the outpatient clinic | Vitamin D level |
| Bhat Y.J., 2017 | Cross-sectional study | 85 | 50 | 35 | 22.4 ± 8.6 | 29.2 ± 7.6 | NR | NR | India | Age- and sex-matched individuals selected randomly from outpatient department with no history of AA | Vitamin D level, serum calcium level |
| Conic R.Z., 2017 | Case-control study | 756 | 584 | 172 | 35.54 ± 19.28 | 35.80 ± 15.56 | 184 (31.50%) | 46 (26.75%) | USA | Age-matched patients given a diagnosis of seborrheic dermatitis without hair loss was randomly selected | Vitamin D deficiency |
| Darwish NMM, 2017 | Case-control study | 50 | 30 | 20 | 28.67 ± 10 | 24.8 ± 6 | 13 (43.3%) | 10 (50%) | Egypt | Age- and sex matched healthy controls | Vitamin D level, serum calcium level |
| Erpolat S, 2017 | Case-control study | 73 | 41 | 32 | 32.8 ± 7.5 | 32.7 ± 7.5 | 26 (63.4%) | 18 (56.3%) | Turkey | Healthy control | Vitamin D level, Vitamin D deficiency, serum calcium level |
| Ghafoor R, 2017 | Case-control study | 60 | 30 | 30 | 23.77 ± 8.86 | 24.03 ± 8.62 | 12 (40%) | 12 (40%) | Pakistan | Healthy volunteers and patients coming to dermatology department for other disorders like acne, melasma, etc. | Vitamin D level |
| Attawa E, 2016 | Cross-sectional study | 46 | 23 | 23 | 26.44 ± 10.87 | 29.39 ± 8.10 | 15 (65.2%) | 14 (60.9%) | Egypt | Healthy controls | Vitamin D level, Vitamin D deficiency |
| Bakry O.A., 2016 | Case-control study | 120 | 60 | 60 | 20.7 ± 10.85 | 23.71 ± 7.45 | 36 (60%) | 28 (46.7%) | Egypt | Age, gender, skin phototype, and body mass index-matched healthy subjects | Vitamin D level, Vitamin D deficiency |
| Fattah N.S.A.A., 2015 | Case-control study | 60 | 30 | 30 | 26.8 ± 6.9 | 25.1 ± 6.9 | 18 (60%) | 18 (60%) | Egypt | Healthy volunteers, matched for age, sex, Fitzpatrick skin phototype, the approximate daily amount of vitamin D intake from food source, the occupation (indoor or outdoor), and time of blood sampling | Vitamin D level, Vitamin D deficiency |
| Aksu Cerman A, 2014 | Cross-sectional study | 144 | 86 | 58 | 32.21 ± 9.60 | 32.55 ± 9.78 | 56 (47.9%) | 34 (29.1%) | Turkey | Age- and sex-matched volunteers from the hospital staff. | Vitamin D level, Vitamin D deficiency |
| Mahamid M, 2014 | Case-control study | 43 | 23 | 20 | 24.2 ± 12.3 | 27 ± 11.26 | 14 (60.87%) | 13 (65%) | Israel | Individuals without a history of AA who were enrolled randomly from clinics | Vitamin D level, Vitamin D deficiency |
| d’Ovidio R, 2013 | Case-control study | 304 | 156 | 148 | 37.8 | 34.5 | 45 (28.85%) | 18 (12.16%) | Italy | Healthy individuals | Vitamin D deficiency |
| El-Mongy NN, 2013 | Case-control study | 140 | 70 | 70 | 27.79 ± 9.116 | 30.49 ± 11.059 | 37 (52.9%) | 44 (62.9%) | Egypt | Normal controls | Vitamin D level, Vitamin D deficiency |
| Yilmaz N, 2012 | Case-control study | 84 | 42 | 42 | 30.8 ± 8.2 | 29.3 ± 7.4 | 14 (33.33%) | 13 (30.95) | Turkey | Healthy individuals | Vitamin D level, serum calcium level |
AA Alopecia areata, NR not reported