Table 1.
Characteristics of study participants from the included studies
| Study | Study design | Country | Groups | Sample size | Age, mean±SD or median (IQR)/range y | Sex, male (%) | Definition of vitamin D status | Levels of vitamin D, mean±SD or median (IQR/range) | Comorbidities | Quality Index |
|---|---|---|---|---|---|---|---|---|---|---|
| D’Avolio et al., 2020 [20] | Retrospective cohort | Switzerland | COVID-19 positive | 27 | 74 (65–81) | 19 (70.4) | NR | 11.1 (8.2–21.0) | NA | Fair |
| COVID-19 negative | 80 | 73 (61–82) | 39 (48.8) | 24.6 (8.9–30.5) | ||||||
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| Darling et al., 2020 [25] | Prospective cohort | UK | COVID-19 positive | 580 | 57.5 (8.7) | 336 (57.5) | NR | 43.3 (32.1) | NA | Fair |
| COVID-19 negative | 723 | 57.9 (8.7) | 377 (52.1) | 44.1 (31.2) | ||||||
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| Raisi-Estabragh et al., 2020 [51] | Prospective cohort | UK | COVID-19 positive | 1326 | 68.11±9.23 | 696 (52.5) | NR | 33.88±27.01 | Diabetes, hypertension, high cholesterol | Good |
| COVID-19 negative | 3184 | 68.91±8.72 | 1,505 (47.3) | 35.45±26.78 | ||||||
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| Hastie et al., 2020 [21] | Retrospective cohort | UK | COVID-19 positive | 449 | 49 (40–58) | 265 (59.0) | Deficiency (<25 nmol/L), Insufficiency (<50 nmol/L) | 28.7 (10.0–43.8) | Diabetes | Good |
| COVID-19 negative | 348 149 | 49 (38–57) | 168 391 (48.4) | 32.7 (10.0–47.2) | ||||||
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| Merzon et al., 2020 [46] | Retrospective cohort | Israel | COVID-19 positive | 782 | 68.11±9.23 | 385 (49.2) | Low (<30 ng/mL) | 19.00 (18.41–19.59) | Diabetes, hypertension, high cholesterol, depression, schizophrenia, dementia, cardiovascular disease, coronary artery disease, chronic lung disorder | Good |
| COVID-19 negative | 7025 | 68.91±8.72 | 397 (50.8) | 20.55 (20.32–20.78) | ||||||
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| De Smet et al., 2020 [26] | Retrospective cohort | Belgium | COVID-19 positive | 186 | 69 (52–80) | 109 (58.6) | Deficiency (<20 ng/mL) | 18.6 (12.6–25.3) | Cardiovascular disease, coronary artery disease, | Good |
| COVID-19 negative | 2717 | 68 (49–82) | 999 (36.8) | 21.5 (13.9–20.8) | ||||||
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| Hernández et al., 2021 [38] | Retrospective case-control | Spain | COVID-19 positive | 197 | 61 (47.5–70) | 123 (62.4) | Deficiency (<20 ng/mL) | 13.8±7.2 | Hypertension, diabetes, cardiovascular disease, chronic lung disease | Fair |
| COVID-19 negative | 197 | 61 (56–66) | 123 (62.4) | 20.9±7.4 | ||||||
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| Abdollahi et al., 2021 [35] | Case-control | Iran | COVID-19 positive | 201 | 24 (19–29) | 66 | Deficient (<10 ng/mL), insufficient (10–30 ng/mL), sufficient (>30–100 ng/mL) | 24 (19–29) | Hypertension, diabetes, chronic lung disease | Fair |
| COVID-19 negative | 201 | 26 (21–35) | 66 | Sufficiency (>30 ng/mL) | 26 (21–35) | |||||
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| Sulli et al., 2021 [41] | Case-control | Italy | COVID-19 positive | 65 | 7.9 (15) | 30 (46.2) | Insufficiency (between 20 and 30 ng/mL), Deficiency (between 10 and 20 ng/mL), and severe deficiency (<10 ng/mL) | 7.9 (15) | Hypertension, diabetes, cardiovascular disease, coronary artery disease, chronic lung disease | Fair |
| COVID-19 negative | 65 | 16.3 (19) | 30 (46.2) | 16.3 (19) | ||||||
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| Alguwaihes et al., 2021 [36] | Retrospective case-control | Saudi Arabia | COVID-19 positive | 150 | 35.8±1.5 | 97 (64.7) | Deficiency (<50 nmol/L) and severe deficiency (<12.5 nmol/L) | 35.8±1.5 | Hypertension, diabetes, cardiovascular disease | Fair |
| COVID-19 negative | 72 | 42.5±3.0 | 38 (52.8) | 42.5±3.0 | ||||||
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| Livingston et al., 2021 [45] | Retrospective cohort | UK | COVID-19 positive | 47 | 38.9±28.2 | 20 (42.6) | Deficiency (<30 nmol/L) | 38.9±28.2 | NA | Fair |
| COVID-19 negative | 57 | 51.0±31.4 | 19 (33.3) | 51.0±31.4 | ||||||
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| Gaudio et al., 2021 [44] | Retrospective cohort | Italy | COVID-19 positive | 50 | 12.5 (2–42) | 26 (52.0) | Deficiency <12 ng/mL (30 nmol/L) and insufficiency 12–20 ng/mL (50 nmol/L) | 12.5 (2–42) | NA | Good |
| COVID-19 negative | 100 | 20.5 (5–46) | 44 (44.0) | 20.5 (5–46) | ||||||
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| Ferrari et al., 2021 [39] | Retrospective cohort | Italy | COVID-19 positive | 188 | 25.1±13.2 | 101 (53.7) | Deficiency (<20 ng/mL) | 25.1±13.2 | NA | Fair |
| COVID-19 negative | 1185 | 26.7±13.3 | 547 (46.1) | 26.7±13.3 | ||||||
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| Al-Daghri et al., 2021 [37] | Case-control | Saudi Arabia | COVID-19 positive | 138 | 55.0±28.8 | 79 (57.2) | Deficiency (<50 nmol/L) | 55.0±28.8 | Hypertension, diabetes, high cholesterol, cardiovascular disease | Fair |
| COVID-19 negative | 82 | 61.8±22.8 | 41 (50.0) | 61.8±22.8 | ||||||
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| Li et al., 2021 [40] | Cohort | USA | COVID-19 positive | 900 | 25 (18–33) | 252 (28.0) | Levels below 20 or 30 ng/mL as low | 25 (18–33) | NA | Good |
| COVID-19 negative | 17 248 | 27 (20–36) | 5726 (33.2) | 27 (20–36) | ||||||
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| Raesi et al., 2021 [52] | Case-control | Iran | COVID-19 positive | 91 | 73.16±23.59 | 55 (60.4) | NR | 73.16±23.59 | Hypertension, diabetes, high cholesterol, cardiovascular disease, chronic lung disorder | Fair |
| COVID-19 negative | 169 | 76.02±23.48 | 113 (66.9) | 76.02±23.48 | ||||||
COVID-19, coronavirus disease 2019; NA, not available; NR, not reported SD, standard deviation; IQR, interquartile range.