Johnston, C. S., Kim, C. M., & Buller, A. J. (2004). Vinegar improves insulin sensitivity to a high-carbohydrate meal in subjects with insulin resistance or type 2 diabetes. Diabetes Care, 27(1), 281-282. In a small crossover trial, ~20 g vinegar taken with a high-carbohydrate meal improved postprandial insulin sensitivity and blunted the glucose/insulin response, most in insulin-resistant subjects. 10.2337/diacare.27.1.281
Kondo, T., Kishi, M., Fushimi, T., Ugajin, S., & Kaga, T. (2009). Vinegar intake reduces body weight, body fat mass, and serum triglyceride levels in obese Japanese subjects. Bioscience, Biotechnology, and Biochemistry, 73(8), 1837-1843. In a 12-week double-blind RCT, 15 or 30 mL/day vinegar produced small reductions in body weight (~1-2 kg), visceral fat, waist, and triglycerides vs placebo; effects regressed after intake stopped. 10.1271/bbb.90231
Hlebowicz, J., Darwiche, G., Bjorgell, O., & Almer, L. O. (2007). Effect of apple cider vinegar on delayed gastric emptying in patients with type 1 diabetes mellitus: a pilot study. BMC Gastroenterology, 7, 46. Ultrasound showed apple cider vinegar slowed gastric emptying of a starchy meal, a plausible mechanism for its blunting of postprandial glycaemia (and a caution in gastroparesis). Pilot: 10 patients with type 1 diabetes and diabetic gastroparesis, investigator-blinded crossover; 300 g rice pudding with 200 ml water, with or without 30 ml apple cider vinegar; median gastric emptying rate 27% without vs 17% with vinegar (p < 0.05). The authors conclude the further slowing might be a disadvantage for glycaemic control in these patients (abstract, PMID 18093343). 10.1186/1471-230X-7-46
Gambon, D. L., Brand, H. S., & Veerman, E. C. I. (2012). Ongezond afslanken. Erosie door appelazijn [Unhealthy weight loss: erosion by apple cider vinegar]. Nederlands Tijdschrift voor Tandheelkunde, 119(12), 589-591. Case report of severe dental erosion in a 15-year-old who drank undiluted apple cider vinegar daily as a weight-loss aid; vinegar pH ~2-3 is well below the enamel demineralization threshold (~5.5). pubmed.ncbi.nlm.nih.gov/23373303