Subgroup analysis
1. Results of main meta‐analysis	Number of studiesa	HbA1c [MD (95% CI)] (number of participants) [trials]	Knowledge [SMD (95% CI)] (number of participants) [trials]	Total cholesterol [MD (95% CI)] (number of participants) [trials]
	14 (3 mo)	‐0.36 [‐0.53, ‐0.18] (n = 1442) [14]	0.35 [0.10, 0.59] (n = 936) [10]	NSS (n = 888) [6]
	22 (6 mo)	‐0.53 [‐0.72, ‐0.35] (n = 1972) [14]	0.50 [0.33, 0.68] (n = 994) [9]	NSS (n = 802) [7]
	12 (1 year)	‐0.19 [‐0.34, ‐0.04] (n = 1966) [9]	0.35 [0.13, 0.57] (n = 328) [2]	NSS (n = 1019) [5]
	4 (2 years)	‐0.33 [‐0.61, ‐0.06] (n = 2268)	no data	no data
2. Type of intervention	Number of studies	HbA1c	Knowledge	Total cholesterol
a. Group education	6 (3 mo)	‐0.14 [‐0.46, 0.18] (n = 703) [5]	0.56 [0.34, 0.77] (n = 557) [4]	NSS (n = 577) [3]
	11 (6 mo)	‐0.46 [‐0.74, ‐0.19] (n = 1075) [5]	NSS (n = 211) [2]	8.92 [7.03, 10.81] (n = 334) [2]
	6 (1 year)	‐0.68 [‐1.19, ‐0.17] (n = 354) [2]	Only 1 study	NSS (n = 356) [2]
	1 (2 years)	One study	No data	No data
b. One‐to‐one education	3 (3 mo)	NSS (n = 204) [3]	NSS (n = 74) [2]	No data
	4 (6 mo)	‐0.41 [‐0.71, ‐0.10] (n = 305) [2]	Only 1 study	One study
	3 (1 year)	NSS (n = 496) [2]	No data	One study
	3 (2 years)	‐0.29 [‐0.57, ‐0.01] (n = 2159)	No data	No data
c. Combined approach	4 (3 mo)	‐0.62 [‐0.99, ‐0.25] (n = 535)	NSS (n = 305)	NSS (n = 390)
	7 (6 mo)	‐0.56 [‐0.76, ‐0.36] (n = 705)	0.47 [0.29, 0.65] (n = 591) [6]	NSS (n = 276) [4]
	3 (1 year)	NSS (n = 511)	Only 1 study	NSS (n = 338) [2]
	0 (2 years)	No data	No data	No data
3. Type of educator	Number of studies	HbA1c	Knowledge	Total cholesterol
a. Link worker/community worker	7 (3 mo)	‐0.36 [‐0.59, ‐0.13] (n = 876)	0.29 [0.04, 0.53] (n = 533) [5]	NSS (n = 399) [3]
	9 (6 mo)	‐0.58 [‐0.89, ‐0.27] (n = 1271)	0.55 [0.29, 0.80] (n = 607) [5]	NSS (n = 668) [5]
	6 (1 year)	‐0.33 [‐0.59, ‐0.07] (n = 1164)	0.35 [0.13, 0.57] (n = 328) [2]	‐0.39 [‐0.64, ‐0.14] (n = 1019) [5]
	4 (2 years)	‐0.33 [‐0.61, ‐0.06] (n = 2268)	No data	No data
b. Diabetes nurse	6 (3 mo)	‐0.49 [‐0.96, ‐0.03] (n = 684)	0.54 [0.24, 0.84] (n = 513) [4]	NSS (n = 536) [4]
	4 (6 mo)	‐0.78 [‐1.18, ‐0.39] (n = 443)	NSS (n = 104) [2]	NSS (n = 334) [3]
	3 (1 year)	NSS (n = 901)	One study	‐0.39 [‐0.64, ‐0.14] (n = 550) [2]
	3 (2 years)	‐0.18 [‐0.34, ‐0.02] (n = 2124)	No data	No data
c. Dietician	4 (3 mo)	NSS (n = 515)	0.53 [0.22, 0.84] (n = 492) [4]	NSS (n = 514) [4]
	7 (6 mo)	‐0.57 [‐0.85, ‐0.29] (n = 815)	0.31 [0.12, 0.50] (n = 451) [5]	NSS (n = 531) [5]
	3 (1 year)	NSS (n = 505)	0.35 [0.13, 0.57] (n = 328) [2]	NSS (n = 336) [2]
	0 (2 years)	No data	No data	No data
4. Duration of the intervention	Number of studies	HbA1c	Knowledge	Total cholesterol
Less than 3 months	9 (3 mo)	NSS (n = 638)	NSS (n = 497) [7]	NSS (n = 304) [3]
	5 (6 mo)	‐0.43 [‐0.64, ‐0.23] (n = 737)	0.43 [0.11, 0.76] (n = 483)	NSS (n = 80) [2]
	0	No data	No data	No data
	1 (2 years)	One study	No data	No data
More than 3 months	5 (3 mo)	‐0.51 [‐0.92, ‐0.11] (n = 804)	0.39 [0.05, 0.73] (n = 439) [3]	NSS (n = 663) [4]
	8 (6 mo)	‐0.65 [‐1.00, ‐0.30] (n = 955)	0.52 [0.34, 0.70] (n = 511) [4]	NSS (n = 530) [4]
	8 (1 year)	‐0.22 [‐0.38, ‐0.05] (n = 1686)	0.35 [0.13, 0.57] (n = 328) [2]	‐0.39 [‐0.64, ‐0.14] (n = 1019) [5]
	3 (2 years)	‐0.29 [‐0.57, ‐0.01] (n = 2159)	No data	No data
5. Health system	Number of studies	HbA1c	Knowledge	Total cholesterol
United States of America and Canada	14 (3 mo)	‐0.47 [‐0.73, ‐0.20] (n = 1442)	0.35 [0.10, 0.59] (n = 936) [10]	NSS (n = 967) [7]
	11 (6 mo)	‐0.62 [‐0.88, ‐0.36] (n = 1387)	0.49 [0.34, 0.65] (n = 722) [7]	NSS (n = 610) [6]
	7 (1 year)	‐0.26 [‐0.45, ‐0.07] (n = 1361)	0.35 [0.13, 0.57] (n = 328) [2]	NSS (n = 694) [4]
	3 (2 years)	NSS (n = 795)	No data	No data
Europe	0 (3 mo)	No data	No data	No data
	2 (6 mo)	‐0.41 [‐0.71, ‐0.10] (n = 305)	NSS (n = 272) [2]	One study
	1 (1 year)	One study	No data	One study
	1 (2 years)	One study	No data	No data
6. Ethnic group	Number of studies	HbA1c	Knowledge	Total cholesterol
a. African American	5 (3 mo)	NSS (n = 482)	NSS (n = 301) [3]	NSS (n = 279) [2]
	4 (6 mo)	‐0.93 [‐1.66, ‐0.21] (n = 400)	0.39 [0.17, 0.60] (n = 346) [3]	NSS (n = 172) [2]
	3 (1 year)	NSS (n = 633)	One study	One study
	2 (2 years)	NSS (n = 651)	No data	No data
b. Hispanic	8 (3 mo)	‐0.33 [‐0.56, ‐0.11] (n = 881)	0.26 [0.03, 0.49] (n = 556) [6]	NSS (n = 609) [4]
	6 (6 mo)	‐0.49 [‐0.77, ‐0.22] (n = 1084)	NSS (n = 297) [3]	NSS (n = 255) [2]
	4 (1 year)	‐0.50 [‐0.77, ‐0.24] (n = 728)	Only 1 study	NSS (n = 583) [3]
	1 (2 years)	One study	No data	No data
c. South Asian	0 (3 mo)	No data	No data	No data
	2 (6 mo)	‐0.41 [‐0.71, ‐0.10] (n = 305)	NSS (n = 272) [2]	One study
	1 (1 year)	One study	No data	One study
	1 (2 years)	One study	No data	No data
aNumber of studies if different from initially stated. CI: confidence interval; HbA1c: glycosylated haemoglobin A1c; MD: mean difference; mo: month; NSS: not statistically significant; SMD: standardised mean difference