The purpose of this open-label non-controlled study is to evaluate the effects of black vinegar intake over the course of 8 weeks on anthropometric measures, cardiometabolic profiles, and insulin sensitivity among adults with impaired glucose tolerance.
After screening, we recruited 32 impaired fasting glucose subjects (14 males and 18 females) with the mean age of 56.3 (from 25 to 65). Black vinegar 50 ml was diluted to 500 ml with drinking water and was given to all subjects for 8 weeks. At baseline and 8-week, all study subjects received 75 grams of Oral Glucose Tolerance Test (OGTT) after 10 hours of fasting. Venous blood was collected at 0, 30, 60, 90 and 120 minutes. Plasma glucose and insulin levels were measured using the glucose oxidase method and radioimmunoassay method. Anthropometric variables including body height, body weight, waist circumference, hip circumference, and body fat were measured using standard methods. BMI and wait-to-hip ratio were calculated to represent body fat distribution. Blood pressure was measured under sitting position after resting for five minutes. Blood lipid profiles including total cholesterol, triglyceride, HDL-C and LDL-C were measured. The Wilcoxon signed-rank test was used to compare the difference between baseline and after eight weeks.
After eight weeks, the body weight and BMI decreased from 68.2±14.4 kg to 67.6±14.2 kg and 26.3±4.5 kg/m2 to 26.0±4.4 kg/m², respectively, with statistical significance (p<0.05). For lipid profiles, triglyceride level decreased from 152.5±134.7 mg/dl to 140.6±93.8 mg/dl but without statistical significance. The blood glucose levels at 120 minutes of OGTT decreased from 178.8±57.0 mg/ dl to 173.7±57.5 mg/dl and the insulin levels at 120 minutes of OGTT increased from 117.5±74.2 IU/L to 126.4±95.9 IU/L but not statistically significant (p>0.05).
From these results, we found that there is a slight decrease of body weight and BMI, but no significantly change in blood pressure, lipid profiles and insulin sensitivity after eight weeks of black vinegar intake among impaired fasting glucose adults. However, further large-scale and longer studies are needed to explore the effects of black vinegar on cardiometabolic profiles and insulin sensitivity.
Keywords: Black vinegar; Anthropometric measures; Lipid profiles; Insulin sensitivity; Impaired glucose tolerance
Obesity and type 2 diabetes mellitus are the most important chronic diseases around the world. They are associated with huge medical expenditure and with increasing morbidity and mortality among related cardio-metabolic diseases in developing and developed countries [1,2].
Vinegar was first reported to have anti-glycemic effects since 1988 in animal and human studies . Vinegar may be associated with improved insulin sensitivity and delayed gastric emptying that accompanied improved glycemic control and reduced body weight [4,5].
Some studies have demonstrated that vinegar intake has some effects in increasing insulin sensitivity and decreasing blood glucose levels in either healthy adults or diabetes subjects [4,6-8]. Vinegar intake with meals can reduce fasting blood glucose levels in healthy adults . A small cross-over study had shown that the postprandial glucose and insulin levels reduction and vinegar can improve insulin sensitivity in healthy and insulin resistant subjects but not for diabetic patients .
But a later study has shown that vinegar can reduce HbA1c level up to 0.16% in diabetes after 12 weeks of regular daily ingestion of vinegar and the positive effects of vinegar intake was found in diabetic subjects .
Whether vinegar is an effective treatment for controlling body weight and improving insulin sensitivity is still controversial . This suggests that the effects of vinegar on weight loss, insulin sensitivity and blood glucose or insulin levels have not been consistent and further studies are needed in different metabolic status subjects.
In total, 32 adults (14 males and 18 females) who have impaired fasting glucose or glucose intolerance were recruited from the outpatient clinic of the Tri-Service General Hospital at Taipei, Taiwan. The criteria for inclusion into this trial were as follows: ages 25–65, absence of infection within the previous three weeks, and no history of malignant tumors. The exclusion criteria were pregnancy, current or a history of cerebrovascular accident, myocardial infarction, heart failure, renal failure, hepatic failure, autoimmune disorders, endocrine diseases, or psychiatric conditions, including mood disorders and alcohol abuse. The subjects allergic to vinegar are also excluded.
All study participants consumed black vinegar 50 ml diluted to 500 ml with drinking water every day for eight weeks. All participants provided written informed consent and agreed to take black vinegar for eight weeks and have their blood samples taken for this study. The institutional review board of our hospital approved this study (Number: TSGHIRB-2-106-65-010).
Body Weight (BW) was measured to an accuracy of 0.1 kg using a standard beam balance scale for participants in barefoot and wearing light indoor clothing. Body height was recorded to the nearest 0.5 cm using a stadiometer.
using a segmental body composition analyzer (TBF-410, Tanita Corp., Tokyo, Japan).
Waist Circumference (WC) was measured to the nearest 0.1 cm at the midpoint between the inferior margin of the last rib and the iliac crest of ilium. Hip circumference (HIP) was measured to the widest of the pelvic region. Body Mass Index (BMI) was calculated using BW (kg) divided by the square of the height (m²). Waist to Hip Ratio (WHR) was also calculated using waist circumference (cm) divided by hip circumference (cm) .
Blood pressures were measured after the subjects had rested for five minutes with cuffs of appropriate sizes and under sitting position. The subjects’ arms were placed at the same height as the heart. Two measurements were recorded and the mean values of two pressures were used for data analyses.
After 10-12 hours of fasting overnight, a 10mL venous blood specimen was collected using venous containers from participants at baseline and after 8-weeks of ingestion of black vinegar while maintaining their usual dietary pattern of the past three days.
Plasma and serum were separated from blood within one hour and stored at −80oC until measurement.
We measured serum total Cholesterol (Chol) using an esterase oxidase method , triglyceride using an enzymatic procedure  on a Hitachi 7150 auto-analyzer (Hitachi, Tokyo, Japan). High- Density Lipoprotein (HDL) and Low-Density Lipoprotein (LDL) cholesterol were measured using an enzymatic method  with magnesium precipitation with the Synchron CX5 analyzer (Beckman Instruments, Palo Alto, California, USA).
We also determined the ratio of total cholesterol to HDL cholesterol (Chol/HDL) as atherogenic index for statistical purposes .
The 75-gm oral glucose tolerance test was conducted after 10 hours of fasting at baseline and after eight weeks of black vinegar intake. 15 ml venous blood specimens were obtained by tail bleeding, before and 30, 60, 90 and 120 minutes after the glucose load to measure glucose and insulin levels.
The plasma glucose concentrations were analyzed immediately after blood sampling and other assays were performed within a 2-week period of the sampling. Plasma glucose concentrations were determined using the glucose oxidase method on a Beckman Glucose Analyzer II (Beckman Instruments, Fullerton, CA) . Plasma insulin concentrations were measured using a commercially available immunoradiometric kit (BioSource Europe S.A., Nivelles, Belgium). The intra-assay and inter-assay coefficients of variance for the insulin measurements were 2.2% and 6.5%, respectively.
Areas under curve were calculated by the trapezoid rule from the start of the meal to 120 min (AUC0–120) .
We used SPSS ver-22 to conduct all statistical analyses. Continuous variables, anthropometric measures, cardiometabolic profiles and insulin sensitivity were described by sample means and SD. The Wilcoxon signed-rank test was used to compare the difference between baseline and after eight weeks of black vinegar intake for each subject. A two-tailed p value less than 0.05 is considered statistically significant.
Table 1 shows the general characteristics of the study subjects at baseline and after eight weeks of vinegar intake. After eight weeks of vinegar intake, the body weight and BMI decreased from 68.2±14.4 kg to 67.6±14.2 kg and 26.3±4.5 kg/m² to 26.0±4.4 kg/m², respectively (p<0.05). For lipid profiles, the triglyceride level also reduced from 152.5±134.7 mg/dl to 140.6±93.8 mg/dl but not statistically significant.
Table 2 compares the difference of insulin sensitivity and metabolic-related profiles between baseline and after eight weeks of vinegar intake. The fasting glucose levels decreased from 106.9±14.7 mg/dl to 105.0±15.0 mg/dl but not statistically significant (p>0.05). The under-curve area of glucose decreased from 448.8±76.6 to 440.1±81.7 (units) but not statistically significant (p>0.05). The AGE level decreased from 7.6±3.9 to 7.1±5.0 but not statistically significant (p>0.05).
Figure 1 shows the change of blood glucose and insulin levels during OGTT at baseline and after eight weeks of vinegar intake. The blood glucose levels at 120 minutes of OGTT decreased from 178.8±57.0 mg/dl to 173.7±57.5 mg/dl and the insulin levels at 120 minutes of OGTT increased from 117.5±74.2 IU/L to 126.4±95.9 IU/L but not statistically significant (p>0.05). The AUC-glucose decreased from 448.8 to 440.1 and AUC-insulin increased from 222.8 to 234.9 but not statistically significant (p>0.05).
Figure 1: Mean blood glucose and insulin levels during oral glucose tolerance test at baseline and after eight weeks of vinegar intake, n=32.
Vinegar is the product of acetic acid and is reported to have anti-glycemic effects in either animal or human studies . The mechanisms of vinegar are based on improved insulin sensitivity and delayed gastric emptying accompanied with improved glycemic control and reduced body weight [5,17-19].
In this study, we found there is a slight decrease of body weight and BMI, but no significantly change in blood pressure, lipid profiles and insulin sensitivity after eight weeks of black vinegar intake among impaired fasting glucose adults. It may be due to the short study period or those subjects are in impaired glucose tolerance but not in diabetic status.
A systemic review and meta-analysis study show that the consumption of vinegar can decrease postprandial glucose and insulin level . Samad et al, reviewed the therapeutic effects of vinegar and shown that daily consumption of vinegar is associated with improvement of chronic disease status such as high blood pressure, hyperlipidemia and obesity. More interestingly, different types of vinegar, such as persimmon or tomato vinegar, is associated with anti-obesity and anti-diabetic effects .
In our study, the results of body weight and BMI reduction were similar to that of the Halima et al study  and Seo et al, study , which showed that apple cider intake could reduce body weight and BMI significantly. However, there is no reduction of lipid profiles in our results, which is not consistent with the Halima et al, and Seo et al, study.
Johnston et al,  showed that fasting glucose level was reduced after 750 mg acetic acid intake per day for 12 weeks, whereas our results indicate that there is no change in fasting glucose and insulin levels. This may be due to insufficient vinegar intake in our study. Larger dosage of vinegar intake may be conducted in the future.
Our results showed that the change of glucose and insulin response and under area curve of OGTT before and after black vinegar intake for eight weeks is not statistically significant. It is not consistent with the results of the Johnston et al study , which indicated that vinegar intake can improve insulin sensitivity for insulin resistant or type 2 diabetes subjects. These inconsistent results may be due to the short duration of study period or the study population with minor cardiometabolic abnormalities. Further studies and larger sample size may be needed to explore the possible mechanism of vinegar on insulin and glucose metabolism.
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