Table 1.

Characteristics of and Risk of Bias in the Included Studies.

Study ID	Study Design and Follow-up Period	Characteristic of the Participants	Intervention Arm/Control Arm	Outcome(s)	Allocation Bias	Performance Bias	Detection Bias	Attrition Bias	Reporting Bias	Other Biases
Johnston 2004	Randomized crossover trial; 1-week washout period Follow-up: 60 minutes	T2DM; n = 10; not on OADs From United States	20 g apple cider vinegar, standard test meal Placebo, standard meal	Plasma glucose at 30 and 60 minutes Plasma insulin at 30 and 60 minutes Whole-body insulin sensitivity	?	↓	↓	↓	↑	↓
Johnston 2008	RCT Follow-up: 12 weeks	T2DM; n = 27; on OADs; age range = 20-80 years; mean age = 63.0 (±4.1) From United States	2 table spoons apple cider vinegar (1400 mg acetic acid); pickle containing 700 mg acetic acid (2.5% acidity) Vinegar pill with 15 mg acetic acid	ALT at 12 weeks AST at 12 weeks Plasma glucose at baseline AEs at <6 weeks and at 6-12 weeks	↓	↑	↓	↓	↓	↓
Johnston 2009	RCT Follow-up: 12 weeks	T2DM; n = 27; on OADs; age range = 20-80 years; mean age = 63.0 (±4.1) From United States	2 table spoons apple cider vinegar (1400 mg acetic acid); pickle containing 700 mg acetic acid (2.5% acidity) Vinegar pill with 15 mg acetic acid	Change in HbA1c at 12 weeks	↓	↑	↓	↓	↓	↓
Johnston 2010	Randomized crossover trial; 1-week washout period Follow-up: 2 hours	T2DM; n = 9; on OADs; mean age = 69 (±2) years From United States	20 g vinegar (1 g acetic acid) Placebo	Change in plasma glucose at 30, 60, 90, and 120 minutes AUC of plasma glucose	?	?	↓	↓	↓	↓
Liatis 2010	Before-after (2 groups—low and high GI mixed meal); 1 week (±2 days) washout period Follow-up: 2 hours	T2DM; n = 16; on OADs or diet alone Low GI group: Mean age = 57.4 (±8.0) years; mean duration of DM = 3.6 (±4.0) years High GI group: Mean age = 61.4 (±8.4) years; mean duration of DM = 4.8 (±3.5) years From Greece	20 g wine vinegar (1.2 g acetic acid), low GI meal; 20 g wine vinegar (1.2 g acetic acid), high GI meal Low GI meal without vinegar; high GI meal without vinegar	Plasma glucose at 30, 60, 90, and 120 minutes Plasma insulin at 30, 60, 90, and 120 minutes AUC of plasma glucose AUC of plasma insulin	↓	↓	↓	↓	↓	↓
Mahmoodi 2013	Nonrandomized controlled trial Follow-up: 1 month	T2DM; n = 60; on OADs; age range = 30-60 years From Iran	15 mL vinegar, standard meal Placebo, standard meal	Plasma glucose at 1 month HbA1c at 1 month	↑	↑	↓	↓	↑	↑
Mitrou 2010	RCT Follow-up: 4 hours	T1DM; n = 10; on insulin; mean age = 32 (±3) years; mean HbA1c = 6.7% (±0.2%); mean duration of DM = 14 (±3) years From Greece	50 mL diluted vinegar Placebo	Plasma glucose at 4 hours AUC of plasma insulin at 4 hours	?	?	↓	↓	↓	↓
Van Dijk 2012	Randomized crossover trial; 1-week washout period Follow-up: 1 week	T2DM; n = 12; on OADs; mean age = 65 (±1) years; mean HbA1c = 6.6% (±0.2%) From Netherlands	25 g white vinegar, glucose beverage Placebo, glucose beverage	Plasma glucose at 30, 60, 90, and 120 minutes Plasma insulin at 30, 60, 90, and 120 minutes	?	?	↓	↓	?	↓
White 2007	Randomized crossover trial; 3-5 days washout period Follow-up: 2 days	T2DM; n = 11; on OADs; age range = 40-72 years; FPG = 7.6 (±0.3) mmol/L; mean HbA1c = 6.2% (±0.2%); mean duration of DM = 4.9 (±1.0) years From United States	2 table spoons of apple cider vinegar, standard meal Placebo, standard meal	Change in fasting plasma glucose at day 2	↑	?	↓	↓	↑	↓
Yoon 2012	RCT Follow-up: 8 weeks	T2DM; n = 72; not on OADs; mean age = 52.8 (±9.9); FPG of 7.0-15.0 mmol/L and HbA1c of 7.0% to 12.0% From South Korea	1500 mg (500 mg tid) ginsam; 2000 mg (1000 mg bid); ginsam 3000 mg (1000 mg tid) ginsam Placebo	HbA1c at 8 weeks Fasting plasma glucose at 8 weeks 2-hour postload plasma glucose at 8 weeks ALT, AST, urinary pH, and leptin at 8 weeks	↓	↓	↓	↓	↓	↓
Ebrahimi 2009	RCT Follow-up: 8 weeks	T2DM; n = 65; mean age = 55.8 (±11.4) From Iran	770 mL apple vinegar; processed Berberis vulgaris No treatment	Fasting plasma glucose at 8 weeks Fasting plasma insulin at 8 weeks BMI, total cholesterol, triglycerides, HDL-C, LDL-C, HOMA-IR at 8 weeks	?	↑	↓	↓	?	↓
Nosrati 2013	Randomized crossover trial; 1-week washout period Follow-up: 90 minutes	T2DM; n = 32; on OADs; mean age = 47.25 (±16.82) From Iran	20 g apple cider vinegar, 40 g water, standard meal Placebo, standard meal	Plasma glucose at 90 minutes Plasma insulin at 90 minutes	↓	?	↓	↓	↓	↓

Abbreviations: T2DM, type 2 diabetes mellitus; OAD, orally administered drug; RCT, randomized controlled drug; ALT, alanine aminotransferase; AST, aspartate aminotransferase; AE, adverse event; AUC, area under the curve; GI, glycemic index; FPG, fasting blood/plasma glucose; BMI, body mass index; HDL-C, high-density lipoprotein cholesterol; LDL-C, low-density lipoprotein cholesterol.