Vitamin D deficiency among outpatients and hospitalized patients with diabetic foot ulcers: A systematic review and meta-analysis

Table 1 Basic characteristics of patients with and without diabetic foot ulcers

Ref.	Study type	Country	Duration	Diabetes	Control	Results
Afarideh et al[18], 2016	Cross-sectional, 30, and 30	Iran	-	41.93 ± 45.48	39.94 ± 26.07	Non-significant, 0.487
Çağlar et al[19], 2018	Prospective, 58 interventions and 47 controls	Turkey	12 mo	7.9 ± 6.3	11.6 ± 6.5	Lower among diabetes, < 0.001
Dai et al[20], 2020	Prospective, 21, and 30	China	9 mo	11.21 ± 5.20	17.73 ± 3.20	Lower among diabetes, < 0.001
Danny Darlington et al[21], 2019	Cross-sectional, 67, and 66	India	-	19.38 ± 5.32	21.91 ± 5.16	No significant difference, 0.306
Feldkamp et al[22], 2018	Cross-sectional, 104, and 103	Germany	-	11.8 ± 11.3	19 ± 14.4	Lower among diabetes, < 0.001
Gupta et al[23], 2016	Retrospective, 50, and 50	India	-	14.25 ± 8.46	21.28 ± 10.98	Lower among diabetes, < 0.001
Tang et al[24], 2021	Prospective, 547, and 1174	China	8 yr	35.8 ± 10.98	45.48 ± 12.91	Lower among diabetes, < 0.001
Tiwari et al[25], 2014	Cross-sectional, 112 cases, 107 controls	India	-	40.2 ± 3.7	49.4 ± 3.2	Lower among diabetes, 0.06
Todorova et al[26], 2020	Cross-sectional, 73, and 169	Bulgaria	-	11.6	13.5	Lower among diabetes, 0.001
Tsitsou et al[27], 2021	Cross-sectional, 33, and 35	Greece	-	17.9 ± 6.7	19.8 ± 8.7	Non-significant, 0.329
Wang et al[28], 2022	Retrospective, 242, 187	China	34 mo	26.89	35.64	Lower among diabetes, < 0.001
Xiao et al[29], 2020	Cross-sectional, 245, and 4039	China	-	36.96 ± 18.03	40.97 ± 17.82	Lower among diabetes, 0.001

Table 2 Age, sex, duration of diabetes, and hemoglobin of patients with and without diabetic foot ulcers

Ref.	Study type	Country	Age	Sex	DM duration	HbA1c
Afarideh et al[18], 2016	Cross-sectional, 30, and 30	Iran	Matched	Matched	Matched	Matched
Çağlar et al[19], 2018	Prospective, 58 interventions and 47 controls	Turkey	Controls younger	Matched	Controls newly diagnosed	Matched
Dai et al[20], 2020	Prospective, 21, and 30	China	Matched	Matched	Matched	Matched
Danny Darlington et al[21], 2019	Cross-sectional, 67, and 66	India	Matched	Matched	Matched	Poor glycemic among foot ulcer
Feldkamp et al[22], 2018	Cross-sectional, 104, and 103	Germany	Matched	Matched	Matched	Matched
Gupta et al[23], 2016	Retrospective, 50, and 50	India	Control was younger	Males high among DM	Lon among diabetes	Poor glycemic among foot ulcer
Tang et al[24], 2021	Prospective, 547, and 1174	China	Control was younger	Higher females in control	Lon among diabetes	Matched
Tiwari et al[25], 2014	Cross-sectional, 112 cases, 107 controls	India	Matched	Matched	Matched	Matched
Todorova et al[26], 2020	Cross-sectional, 73, and 169	Bulgaria	Control was younger	Matched	Matched	NA
Tsitsou et al[27], 2021	Cross-sectional, 33, and 35	Greece	Matched	Matched	Matched	Matched
Wang et al[28], 2022	Retrospective, 242, 187	China	Control was younger	Males higher among DM	Lon among diabetes	NA
Xiao et al[29], 2020	Cross-sectional, 245, and 4039	China	Matched	Females more	Matched	Poor glycemic among foot ulcer

DM: Diabetes mellitus; HbA1c: Hemoglobin A1c; NA: Not available.

Table 3 Newcastle Ottawa scale risk of bias of the included studies

Ref.	Country	Selection bias	Comparability bias	Outcome	Total score
Afarideh et al[18], 2016	Iran	4	2	2	8
Çağlar et al[19], 2018	Turkey	4	2	2	8
Dai et al[20], 2020	China	4	2	2	8
Danny Darlington et al[21], 2019		4	1	2	7
Feldkamp et al[22], 2018	India	4	2	2	8
Gupta et al[23], 2016	Germany	4	2	2	8
Tang et al[24], 2021	India	4	2	2	8
Tiwari et al[25], 2014	China	4	1	2	7
Todorova et al[26], 2020	India	4	2	2	8
Tsitsou et al[27], 2021	Bulgaria	4	1	2	7
Wang et al[28], 2022	Greece	4	2	2	8
Xiao et al[29], 2020	China	4	1	2	7