What clinical trials have compared apple cider vinegar to placebo for A1c outcomes in type 2 diabetes?
Executive summary
A small but growing set of controlled clinical trials has directly compared apple cider vinegar (ACV) to placebo or control and reported hemoglobin A1c (HbA1c) outcomes in people with type 2 diabetes; several individual randomized trials reported reductions in HbA1c while recent systematic reviews caution that results are inconsistent and limited by heterogeneity and small sample sizes [1] [2]. The evidence base includes at least a half-dozen controlled trials referenced across reviews and meta‑analyses, but firm clinical guidance is precluded by variable designs, comparators and quality concerns [3] [4].
1. What the randomized trials say: named studies and their findings
A prominent randomized controlled trial published in 2023 by Jafarirad and colleagues tested daily ACV (30 mL/day) versus control in adults with type 2 diabetes and reported a significant between‑group difference in HbA1c after eight weeks (p < 0.001), along with improvements in LDL and cholesterol ratios in the ACV arm [1] [5]. Other single‑center randomized trials cited in the literature include a 2019 “randomized placebo controlled design” reported by Kausar et al. (Int J Med Res Health Sci) and older trials such as Mohammadpourhodki & Sargolzaei (Prensa Medica Argentina) that are listed in systematic reviews as having measured glycosylated hemoglobin [6] [7] [4]. Systematic searches and narrative reviews also identify additional parallel and crossover trials that tested vinegar (including ACV) against placebo and measured A1c or long‑term glycemic outcomes [8] [9].
2. How many trials and participants have been pooled by reviewers
A dose‑response, GRADE‑assessed systematic review and meta‑analysis published in January 2025 assembled controlled clinical trials of ACV in type 2 diabetes but concluded that the evidence is conflicting; earlier meta‑analytic summaries reported a small number of trials—meta‑analyses have pooled roughly six relevant trials including several hundred patients in aggregate in prior reviews (for example, “six studies, 317 patients” is reported in one synthesis cited in the literature) [2] [3]. These pooled efforts identify HbA1c and fasting glucose as common endpoints but also flag that trials differ in duration, dose and control selection [3] [4].
3. Design heterogeneity that complicates interpretation
Trials vary widely: some are parallel randomized double‑blind trials using water or inert solutions as placebo, others are crossover studies investigating acute postprandial responses, and at least one trial compared multiple doses of vinegar to placebo rather than a single standardized ACV regimen [8] [9] [4]. Durations range from single meal/crossover experiments to multi‑week interventions (e.g., eight weeks in Jafarirad et al.), and concomitant diabetes treatments and diet advice were handled inconsistently across studies, producing heterogeneity that limits definitive pooling [1] [9] [10].
4. Quality signals, language and publication considerations
Systematic reviewers note that trials include non‑English reports (Persian, others) and small sample sizes, and that some trials are published in regional journals with varying reporting standards—issues that trigger GRADE downgrades and caution about overinterpreting single positive trials [4] [3]. The most recent GRADE‑assessed meta‑analysis explicitly states evidence is conflicting and of variable certainty, even while individual trials report significant HbA1c changes [2] [4].
5. Bottom line for A1c outcomes
Multiple controlled clinical trials have directly compared ACV or vinegar to a placebo or control and reported HbA1c outcomes—some trials (for example Jafarirad et al.) show statistically significant reductions in HbA1c over short follow‑up, while systematic reviews that pool these trials conclude that the overall evidence is inconsistent and limited by heterogeneity, small N and study quality concerns [1] [2] [3]. Given these constraints, ACV cannot yet be endorsed as a reliably effective, evidence‑backed intervention for lowering A1c in type 2 diabetes; further larger, well‑blinded, standardized RCTs are explicitly called for in the reviews [2] [4].