Hey there, folks! If you’re one of those health nuts (like me) who swears by a daily shot of apple cider vinegar—y’know, that funky, tangy stuff we call ACV—you might be wonderin’ if it’s cool to keep sippin’ it right before a blood test. Well, lemme cut to the chase: nah, it’s generally best to skip it. Why? ‘Cause ACV can mess with stuff like your blood sugar and electrolytes, potentially throwin’ off your test results. And trust me, you don’t wanna risk a doc misreadin’ your health stats over a lil’ vinegar habit.
At our lil’ corner of the internet here, we’re all about keepin’ things real and practical. So, I’m gonna break down why you might wanna hold off on that ACV before your blood draw, how it could impact different tests, and what you should do instead to prep like a pro. Plus, we’ll chat about some other blood test tips and even dive into the whole ACV craze—why folks love it, and if it’s really all it’s cracked up to be. Stick with me, ‘cause we’ve got a lotta ground to cover!
Why Avoid Apple Cider Vinegar Before a Blood Test?
Alright, let’s get into the nitty-gritty. Blood tests are like a snapshot of what’s goin’ on inside ya—your sugar levels, cholesterol, electrolytes, all that jazz. Anything you eat or drink can tweak that picture, and ACV ain’t no exception. Here’s why it’s a risky move to down some before headin’ to the lab:
- Blood Sugar Shenanigans: ACV’s got this rep for helpin’ with insulin sensitivity and lowerin’ blood glucose in some folks. Sounds great, right? But if you’re gettin’ a glucose test, that effect could make your levels look lower than they really are. For peeps with diabetes or on meds for blood sugar, this could even be mistaken for somethin’ serious like hypoglycemia. Even if you ain’t diabetic, it might still mess with how docs read your sugar tolerance.
- Electrolyte Interference: ACV has acetic acid, which can play around with stuff like potassium levels in your blood. Now, it’s usually a tiny change, but even a small swing in electrolytes can raise eyebrows on a test result. Potassium outta whack can be a big deal, and you don’t want no false alarms.
- Other Weird Effects: There’s also some trace minerals and acids in ACV that might nudge other blood markers. It ain’t super common, but why gamble with accuracy when it’s your health on the line?
Bottom line? If you wanna make sure your blood test shows the real you, lay off the ACV for at least 24 hours before the needle comes out. That gives your body time to clear it outta your system and not mess with the numbers.
How Long Should You Stop Drinkin’ ACV Before the Test?
So, you’re probably thinkin’, “Okay, I’ll skip it, but for how long?” Good question! As a general rule of thumb, stop takin’ ACV—whether it’s the liquid kind or them fancy capsules—at least a full day (24 hours) before your blood test. That’s plenty of time for your body to process it and get back to baseline. If you’re takin’ big ol’ doses daily or got specific health stuff goin’ on, your doc might even say to pause it for longer. When in doubt, chat with ‘em.
And hey, if you’re usin’ ACV for somethin’ like weight loss or digestion, don’t stress—skippin’ it for a day or two ain’t gonna derail your goals You can pick right back up after the test is done.
Does the Amount of ACV Matter?
Now, you might be wonderin’ if a tiny splash in your water is as bad as chuggin’ a whole shot. Fair point! The truth is, yeah, the amount does play a role. A small sip prob’ly won’t rock the boat as much as a hefty dose, but it still could nudge your glucose or potassium just enough to throw things off. Larger amounts are way more likely to cause noticeable changes, so play it safe and just avoid it altogether before the test. Better safe than sorry, ya know?
What If I Already Drank Some ACV? Panic Time?
Oops, did ya accidentally sip some ACV this mornin’ before rememberin’ your test? Don’t freak out just yet First thing, tell the person drawin’ your blood or your doc about it as soon as you can They’ll figure out if it’s a big deal based on what kinda test you’re havin’. They might go ahead with it, or they might reschedule to make sure the results ain’t funky. Honesty’s the best policy here—don’t try to hide it, ‘cause that could mess with how they read your health.
How ACV Impacts Specific Blood Tests
Not all blood tests are the same and ACV might mess with some more than others. Let’s break down a few common ones and how that vinegar could stir the pot
- Glucose Tests: Like I said earlier, this is the biggie. ACV can lower blood sugar, so if you’re testin’ for diabetes, prediabetes, or just checkin’ your levels, it could make things look off. This includes fastin’ glucose tests or them oral glucose tolerance ones (especially for pregnant folks checkin’ for gestational diabetes).
- Electrolyte Panels: If your doc’s lookin’ at stuff like potassium or sodium, ACV might cause a lil’ blip in the readings. Ain’t usually a huge shift, but enough to maybe confuse things.
- Cholesterol Tests (Lipid Panels): Some folks think ACV can help with cholesterol over time, but a quick dose before a test prob’ly won’t change much. Still, it’s best to avoid it since these tests often need you to fast anyway.
- Liver or Kidney Function Tests: There ain’t much proof that ACV directly tweaks these results in a short window, but if you’ve got existin’ issues or take it a ton, it’s worth mentionin’ to your doc. Long-term overuse might stress kidneys a bit, though.
- Thyroid Tests: Limited info says ACV messes with thyroid hormones, but we ain’t takin’ chances. Tell your healthcare peeps you use it.
- Vitamin Deficiency Tests: ACV’s got trace nutrients like potassium. If you’re testin’ for deficiencies in somethin’ it contains, hold off for a day so it don’t skew the numbers even a smidge.
When you ain’t sure what test you’re gettin’, or if ACV could mess with it, just skip it for 24 hours and ask your doc. They’ll steer ya right.
General Prep Tips for a Blood Test (Beyond Skippin’ ACV)
While we’re on the topic of blood tests, let’s talk about gettin’ ready in general. ACV ain’t the only thing that can mess with results—there’s a buncha stuff to keep in mind. I’ve been through my fair share of these tests, and lemme tell ya, followin’ the rules makes a big diff. Here’s what we’ve learned over at our camp:
- Fasting Rules: Some tests, like lipid panels (cholesterol) or glucose checks, need you to fast for 8-12 hours beforehand. That means no food, no drinks—nada, except plain water. Check with your doc if you gotta fast, and for how long.
- Hydrate Like Crazy: Drink plenty of water in the days leadin’ up to the test. Bein’ dehydrated can mess with blood volume and make electrolyte levels look weird. Just stick to plain H2O, no flavored or fizzy stuff.
- Skip the Booze and Caffeine: Lay off alcohol and too much coffee for at least a day before. They can mess with hydration and other markers.
- Medications and Supplements: Ask your doc if you should pause any meds or vitamins before the test. Some can alter results, and you don’t wanna risk it.
- Timing Your Test: If fastin’ is tough for ya, book an early mornin’ slot. That way, you sleep through most of the no-eatin’ part. If it’s later, have a hearty meal with protein and good fats before the fast starts to keep ya full.
Here’s a quick lil’ table to sum up fastin’ needs for common tests:
| Test Type | Fasting Needed? | How Long? | What’s Allowed? |
|---|---|---|---|
| Lipid Panel (Cholesterol) | Yes | 12 hours | Water only |
| Blood Glucose Test | Yes | 8 hours minimum | Water only |
| Basic Metabolic Panel | Sometimes | 8-12 hours if yes | Water only |
| Liver Function Test | Sometimes | 8-12 hours if yes | Water only |
| Kidney Function Test | Sometimes | 8-12 hours if yes | Water only |
Always double-check with your healthcare crew, ‘cause rules can vary based on what they’re lookin’ for.
Why’s Everyone So Crazy About Apple Cider Vinegar Anyway?
Okay, let’s take a quick detour and chat about why so many of us are guzzlin’ ACV in the first place. I mean, it’s got this weird, sharp taste, yet folks swear by it! I’ve tried it myself for a spell, and here’s the deal on why it’s such a hot topic—and why it’s tough to skip even for a day before a test.
ACV is basically fermented apple juice, and it’s been hyped up for all kinda health perks. Some peeps say it helps with digestion, boosts weight loss, clears up skin, and even keeps blood sugar in check. I ain’t gonna lie, I started mixin’ a spoonful in water every mornin’ hopin’ it’d help with bloat, and it kinda did feel like it worked. But here’s the catch—there ain’t a ton of hard proof for all these claims. Some small studies back up the blood sugar thing, especially for folks with insulin issues, but a lotta the other benefits are more like old wives’ tales than science.
Still, it’s cheap, easy to find, and feels like a “natural” fix, so we keep comin’ back to it. Problem is, that same stuff that might help day-to-day can be a pain when you need accurate medical results. So, while I get the love for ACV, sometimes ya gotta put it on hold for the bigger picture.
Risks of Overdoin’ It With ACV (Even Outside of Tests)
While we’re at it, let’s talk about usin’ ACV too much in general. I know some folks who go hardcore, takin’ shots of it straight up multiple times a day. That ain’t always a great idea, fam. Here’s why overdoin’ it can backfire:
- Tooth Enamel Damage: That acid in ACV can wear down your teeth over time if you ain’t dilutin’ it or rinsin’ your mouth after. I learned that the hard way with some sensitivity—ouch!
- Stomach Irritation: Too much can irritate your gut, givin’ ya heartburn or nausea. Always mix it with water, don’t go raw.
- Potassium Drops: Drinkin’ loads long-term might lower potassium too much, which is risky for your heart and muscles.
- Drug Interactions: If you’re on meds for diabetes or diuretics, ACV could mess with how they work. Gotta check with your doc.
Moderation’s the name of the game. A tablespoon or two a day, mixed in water, is usually fine for most of us. But again, pause it before bloodwork to keep things straight.
Common Questions About ACV and Blood Tests
I’ve heard a lotta the same worries pop up when peeps ask about ACV and blood tests. So, let’s tackle some FAQs to clear the air. If you’ve got these on your mind, I gotchu covered!
- Can I drink water with ACV before the test? Nope, sorry. Even in water, it’s still ACV doin’ its thing. Stick to plain water to be safe.
- Does it matter if it’s liquid or capsules? Kinda, but not really. Liquid might hit your system faster, but both can affect results if taken close to the test. Avoid ‘em both for 24 hours prior.
- What if I’m usin’ ACV for weight loss—do I gotta stop forever? Nah, just for a day before the test. It won’t mess up your progress. Pick it back up after.
- Will ACV mess with every single blood test? Not necessarily, but since it can impact glucose and electrolytes, it’s a risk for many common ones. Play it safe and ask your doc if you ain’t sure.
- Is it cool to take ACV right after the test? Yup, once the blood’s drawn, you’re usually good to go back to your routine. Just keep an eye on sugar levels if you’ve got diabetes or related meds.
Got more questions? Drop ‘em to your healthcare provider. They’ll give ya the straight dope for your specific sitch.
Wrappin’ Up: Play It Safe With ACV and Blood Tests
So, there ya have it—everything we could think of about whether you should drink apple cider vinegar before a blood test. To sum it up, it’s best to skip it for at least 24 hours before headin’ to the lab. It could mess with your blood sugar, electrolytes, and maybe other stuff, leadin’ to results that don’t show the real you. And when it comes to your health, accuracy is everythin’.
We’ve covered how ACV works, why folks dig it, how to prep for blood tests in general, and even some risks of overusin’ it. My advice? Always chat with your doc or the lab peeps about what you’re takin’—be it ACV or anything else. Follow their rules to a T, stay hydrated, and don’t sweat skippin’ your vinegar fix for a day. Your test results (and peace of mind) are worth it.
Got any weird blood test stories or ACV hacks? I’d love to hear ‘em! Drop a comment below, and let’s keep this convo rollin’. Stay healthy out there, y’all!
Amir Hadi1Department of Clinical Nutrition, School of Nutrition and Food Science, Isfahan University of Medical Sciences, Isfahan, Iran Find articles by
Received 2020 Oct 14; Accepted 2021 Jun 8; Collection date 2021. © The Author(s) 2021
Open AccessThis article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The s or other third party material in this article are included in the articles Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the articles Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated in a credit line to the data.
Elevated lipid profiles and impaired glucose homeostasis are risk factors for several cardiovascular diseases (CVDs), which, subsequently, represent a leading cause of early mortality, worldwide. The aim of the current study was to conduct a systematic review and meta-analysis of the effect of apple cider vinegar (ACV) on lipid profiles and glycemic parameters in adults.
A systematic search was conducted in electronic databases, including Medline, Scopus, Cochrane Library, and Web of Knowledge, from database inception to January 2020. All clinical trials which investigated the effect of ACV on lipid profiles and glycemic indicators were included. Studies were excluded if ACV was used in combination with other interventions or when the duration of intervention was < 2 weeks. To account for between-study heterogeneity, we performed meta-analysis using a random-effects model.
Overall, nine studies, including 10 study arms, were included in this meta-analysis. We found that ACV consumption significantly decreased serum total cholesterol (− 6.06 mg/dL; 95% CI: − 10.95, − 1.17; I2: 39%), fasting plasma glucose (− 7.97 mg/dL; 95% CI: − 13.74, − 2.21; I2: 75%), and HbA1C concentrations (− 0.50; 95% CI: − 0.90, − 0.09; I2: 91%). No significant effect of ACV consumption was found on serum LDL-C, HDL-C, fasting insulin concentrations, or HOMA-IR. The stratified analysis revealed a significant reduction of serum TC and TG in a subgroup of patients with type 2 diabetes, those who took ≤15 mL/day of ACV, and those who consumed ACV for > 8-weeks, respectively. Furthermore, ACV consumption significantly decreased FPG levels in a subgroup of studies that administered ACV for > 8-weeks. Further, ACV intake appeared to elicit an increase in FPG and HDL-C concentrations in apparently healthy participants.
We found a significant favorable effect of ACV consumption on FPG and blood lipid levels.
The online version contains supplementary material available at 10.1186/s12906-021-03351-w.
Keywords: Apple cider vinegar, Lipid profiles, Clinical trials, Meta-analysis, Glycemic indices
Cardiovascular diseases (CVDs), collectively, are regarded as the number one cause of early mortality, worldwide [30]. According to the World Health Organization (WHO), approximately 17.7 million deaths were attributable to CVD in 2015, and it is projected to account for more than 23.6 million by 2030 [2]. Indeed, given the high economic costs of CVDs on healthcare systems, especially in developing countries, prevention and management of CVDs is of high priority.
Dyslipidemia, in particular hypercholesterolemia, and hyperglycemia are regarded as the most important contributors to CVD events [24, 25]. Lifestyle modifications (dietary changes and physical activity), along with pharmacological interventions, such as statins, fibrates, and insulin sensitizers, are routinely used to manage these metabolic disorders [1, 14, 19, 26]. However, low adherence to lifestyle recommendations and reported adverse reactions of synthetic agents [38, 41] highlights the necessity of discerning novel and efficacious approaches. In this line, the benefical effect of nutraceutics and fuctional foods on human health have been well-documented [8, 36]. In contemporary research and practice, plants and their derivatives have attracted a lot of interest for their beneficial effects in controlling lipid profile and glycemic status [5, 15, 37]. Indeed, one of the most popular plant derivatives in this regard is vinegar.
Apple cider vinegar (ACV) is one of the three most common types of vinegar, produced by fermenting apples [3]. This acidic solution is consumed throughout the world as a flavoring and preservative agent in foods [22]. ACV contains a variety of flavonoids, such as gallic acid, catechin, caffeic acid, and ferulic acid [11, 31]. Animal experiments have reported that ACV has a variety of pharmacological functions, including anti-oxidant, anti-inflammatory, anti-diabetic, anti-hypertensive, and anti-hyperlipidemic properties [7, 18, 32, 39]. The effects of ACV on serum lipid parameters and glycemic markers have been investigated in several randomized clinical trials [4, 12, 16, 22, 23, 27, 33]; however, the results are equivocal. Indeed, some investigations have reported beneficial effects following ACV consumption on the aforementioned parameters [16, 22, 23, 27], although others failed to detect any effects [4, 12, 33]. It is conceivable that such contradictory findings might be due to the differences in study design and/or characteristics of participants (age, sex, clinical condition).
To the best of our knowledge, there has been no systematic compilation of the previously reported effects of ACV on lipid profiles and glycemic status. Therefore, in the current study, we performed a systematic review and meta-analysis of all published clinical trials to provide a more precise estimation of the effects of ACV on serum lipid parameters and glycemic markers in adults.
The present systematic review and meta-analysis was planned, conducted, and reported according to the guidelines of the 2009 Preferred Reporting Items for Systematic Reviews and Meta- Analysis (PRISMA) statement [29].
A comprehensive literature search was performed to identify and appraise investigations that had assessed the effects of ACV supplementation on lipid profiles and glycemic parameters. Electronic databases, including Medline, Scopus, Cochrane Library, and Web of Knowledge, were searched from database inception to January 2020. The relevant keywords were used in combination with the Medical Subject Heading (MeSH) terms, search tag, and boolean operators (AND, OR, NOT) (Supplemental Table 1). The search keywords were seldom based on vinegar and related phrases to minimize the chance of missing studies which reported lipids or glycemic related markers as secondary outcomes. Additionally, the reference lists of related review articles and the retrieved studies were also hand-searched to detect eligible trials that might have been missed.
After excluding duplicate studies, two authors (AH and MP) independently reviewed articles based on titles, abstracts, or full-texts to identify relevant studies. Eventually, original studies were included in the present meta-analysis if they: 1) were randomized clinical trials; 2) administered ACV as the intervention; 3) enrolled adult participants (aged ≥18 years); 4) reported lipid and glycemic parameters as the outcomes of interest. Studies that met the following criteria were excluded: 1) ACV was used in combination with other interventions; 2) studies with an intervention duration of fewer than 2 weeks; 3) studies that did not report relevant effect sizes. Table 1 shows the PICOS (participants, intervention/exposure, comparisons, outcomes, and study design) criteria which was used to define the research question.
PICO (participants, intervention/exposure, comparison, outcomes, and study design) criteria for inclusion and exclusion of studies
| Parameters | Descriptions |
|---|---|
| Participants | Adult |
| Intervention | Apple cider vinegar supplementation |
| Comparison | Any comparator/control that incorporated a nonintervention group |
| Outcomes | lipid profile levels and glycemic indices |
| Setting | Randomized controlled trials |
Risk of bias assessment
The author’s judgment on each criterion of the risk of bias assessment is presented in Table 3. In summary, 8 trials [4, 12, 16, 20, 22, 23, 28, 33] were randomized, however, only 3 studies [20, 22, 33] had provided enough information regarding allocation concealment. Three studies [20, 23, 33] were blinded. Seven studies [4, 12, 20, 22, 23, 28, 33] had low attrition bias and/or described the reason of participants’ withdrawal. Three trials had reported the controlling of other factors that may influence outcomes [4, 20, 22].
The summary of review authors’ judgments about each risk of bias item for included studies
| Study | Random sequence generation | Allocation concealment | Blinding | Incomplete outcome data | Selective reporting | Other bias |
|---|---|---|---|---|---|---|
| Bashiri et al. [4] | L | U | H | L | L | L |
| Halima et al. [16] | L | U | U | U | L | U |
| Kondo et al. [23] | L | U | L | L | L | U |
| Mahmoodi et al. [27] | U | H | U | U | L | U |
| Panetta et al. [33] | L | L | L | L | L | U |
| Khezri et al. (2018) [22] | L | L | H | L | L | L |
| Ebrahimi-Mamaghani et al. [12] | L | U | H | L | L | U |
| Mohammadpourhodki et al. (2019) [28] | L | U | H | L | L | U |
| Kausar et al. (2019) [20] | L | L | L | L | L | L |
Findings from 8 studies, with 9 effect sizes, revealed that ACV consumption significantly decreased serum TC concentrations (− 6.06 mg/dL; 95% CI: − 10.95, − 1.17, P = 0.02; I2: 39%). In addition, a trend toward a significant reduction in serum TG levels was also seen following ACV consumption (− 33.66 mg/dL; 95% CI: − 67.87, 0.54, P = 0.05; I2: 95%). No significant effect of ACV consumption on serum LDL-C (− 2.12 mg/dL; 95% CI: − 10.09, 5.85, P = 0.60; I2: 81%) and HDL-C concentrations was found after ACV consumption (0.92 mg/dL; 95% CI: − 0.42, 2.27, P = 0.18; I2: 22%) (Fig. 2).
The meta-analysis results of the effect of apple cider vinegar administration on lipids profiles. Kondo et al. study administrated apple cider vinegar in 2 different dosages which showed as “L” (lower dose) and “H” (higher dose) in figure
To discern the source of heterogeneity, we performed subgroup analyses based on participant’s condition, dose of ACV consumption, and the duration of intervention. In these analyses, we found a notable decrease in both TG and TC concentrations in studies conducted on type 2 diabetic patients (TG: − 22.46 mg/dL; 95% CI: − 40.27, − 4.65; I2: 0%; TC: − 11.51 mg/dL; 95% CI: − 18.16, − 4.86; I2: 0%), as well as in studies with an ACV dose of ≤15 mL/day (TG: − 21.91 mg/dL; 95% CI: − 35.23, − 8.60; I2: 0%; TC: − 10.22 mg/dL; 95% CI: − 16.46, − 3.98; I2: 0%) and studies with > 8-weeks of intervention (TG: − 48.22 mg/dL; 95% CI: − 92.83, − 3.60; I2: 96%; TC: − 7.61 mg/dL; 95% CI: − 14.29, − 0.94; I2: 49%). However, no significant reduction in these variables was found in studies conducted on non-diabetics, studies that administered > 15 mL/day, and those with a duration of intervention of ≤8-weeks. In addition, a significant increase in serum HDL-C levels was observed in studies that recruited non-diabetics (HDL-C: 1.73 mg/dL; 95% CI: 0.28, 3.18; I2: 0%) (Table 4).
| Variables | Subgroup analysis based on | Number of trials | Mean difference (95%CI) | Within study heterogeneity | Between study heterogeneity | |
|---|---|---|---|---|---|---|
| TG | Participants condition | Type 2 diabetes | 5 | −22.46 (−40.27, −4.65) | 0% | 0.001 |
| Other condition | 4 | −40.86 (−93.61, 11.88) | 97% | |||
| Amount of apple vinegar | > 15 mL/day | 5 | − 47.59 (−101.58, 6.67) | 96% | < 0.001 | |
| ≤ 15 mL/day | 4 | −21.91 (−35.23, −8.60) | 0% | |||
| Duration | > 8 weeks | 4 | −48.22 (−92.83, − 3.60) | 96% | < 0.001 | |
| ≤ 8 weeks | 5 | −9.51 (− 33.63, 14.60) | 32% | |||
| TC | Participants condition | Type 2 diabetes | 5 | −11.51 (− 18.16, −4.86) | 0% | 0.01 |
| Other condition | 4 | −3.21 (−8.81, 2.40) | 47% | |||
| Amount of apple vinegar | > 15 mL/day | 5 | −4.00 (−10.19, 2.19) | 46% | 0.03 | |
| ≤ 15 mL/day | 4 | −10.22 (− 16.46, −3.98) | 0% | |||
| Duration | > 8 weeks | 4 | −7.61 (−14.29, −0.94) | 49% | 0.75 | |
| ≤ 8 weeks | 5 | −5.71 (−14.33, 2.92) | 49% | |||
| LDL-C | Participants condition | Type 2 diabetes | 5 | −5.39 (− 14.31, 3.53) | 48% | 0.002 |
| Other condition | 4 | 1.62 (−9.85, 5.85) | 87% | |||
| Amount of apple vinegar | > 15 mL/day | 5 | −0.59 (−11.73, 10.55) | 85% | 0.003 | |
| ≤ 15 mL/day | 4 | −4.34 (−12.51, 3.84) | 38% | |||
| Duration | > 8 weeks | 4 | −1.41 (− 16.36, 13.55) | 90% | 0.02 | |
| ≤ 8 weeks | 5 | −1.66 (−8.83, 5.51) | 38% | |||
| HDL-C | Participants condition | Type 2 diabetes | 5 | 0.21 (−2.17, 2.60) | 34% | 0.10 |
| Other condition | 4 | 1.73 (0.28, 3.18) | 0% | |||
| Amount of apple vinegar | > 15 mL/day | 5 | 0.39 (−1.78, 2.57) | 56% | 0.49 | |
| ≤ 15 mL/day | 4 | 1.61 (−0.52, 3.75) | 0% | |||
| Duration | > 8 weeks | 4 | 1.62 (− 0.07, 3.30) | 0% | 0.32 | |
| ≤ 8 weeks | 5 | 0.52 (−1.75, 2.79) | 48% | |||
| FPG | Participants condition | Type 2 diabetes | 5 | −16.28 (−33.02, 0.47) | 83% | 0.69 |
| Other condition | 2 | −3.53 (−6.70, −0.37) | 0% | |||
| Amount of apple vinegar | > 15 mL/day | 3 | −16.12 (−41.31, 9.07) | 87% | 0.15 | |
| ≤ 15 mL/day | 4 | −4.10 (−8.98, 0.76) | 52% | |||
| Duration | > 8 weeks | 3 | −3.78 (− 6.90, −0.66) | 0% | 0.55 | |
| ≤ 8 weeks | 4 | −17.14 (−38.15, 3.86) | 86% | |||
| HbA1C | Participants condition | Type 2 diabetes | 3 | −0.77 (−1.56, 0.02) | 88% | 0.001 |
| Other condition | 3 | −0.07 (− 0.32, 0.18) | 0% | |||
| Amount of apple vinegar | > 15 mL/day | 3 | −0.60 (−1.54, 0.33) | 92% | 0.13 | |
| ≤ 15 mL/day | 3 | −0.24 (− 0.51, 0.03) | 10% | |||
| Duration | > 8 weeks | 3 | −0.72 (−1.58, 0.15) | 90% | 0.01 | |
| ≤ 8 weeks | 3 | −0.14 (− 0.43, 0.15) | 23% | |||
Pooled effect size from 6 studies, with 7 effect sizes, revealed a significant reduction in FPG (− 7.97 mg/dL; 95% CI: − 13.74, − 2.21, P = 0.007; I2: 75%) after ACV consumption. The same findings were obtained for HbA1C, when we combined 6 effect sizes from 5 studies (− 0.50 mg/dL; 95% CI: − 0.90, − 0.09, P = 0.02; I2: 91%). No significant effect of ACV consumption was found on serum insulin levels (− 0.85 mg/dL; 95% CI: − 2.73, 1.02, P = 0.37; I2: 0%) and HOMA-IR (− 0.31 mg/dL; 95% CI: − 0.80, 0.17, P = 0.21; I2: 18%) (Fig. 3).
The meta-analysis results of the effect of apple cider vinegar administration on glycemic related factors. Kondo et al. study administrated apple cider vinegar in 2 different dosages which showed as “L” (lower dose) and “H” (higher dose) in figure
Subgroup analysis revealed a significant reduction in FPG in studies recruited non-diabetics (− 3.53 mg/dL; 95% CI: − 6.70, − 0.37; I2: 0%). Such an effect was not observed in studies that enrolled diabetic patients (− 16.28 mg/dL; 95% CI: − 33.02, − 0.47; I2: 83%). Furthermore, when studies were stratified based on duration of intervention, the lowering effect of ACV on FPG was found in studies with an intervention of > 8-weeks follow-up (− 3.78 mg/dL; 95% CI: − 6.90, − 0.66; I2: 0%). No significant effect of ACV consumption on FPG was seen in studies with a low or high dose of ACV. When we excluded the study of Mohammadpourhodki et al. (36), between-study heterogeneity became non-significant (− 3.09 mg/dL; 95% CI: − 5.83, − 0.35; I2:23%). In addition, the lowering effect of ACV on HbA1C was non-significant in all subgroups (Table 4). Due to the low number of trials in each subgroup, stratified analysis was not conducted for serum insulin levels and HOMA-IR.
Findings from the meta-regression indicated an inverse association between change in FPG and HbA1C levels and baseline levels of these indicators (FPG: coefficient: -0.24; 95% CI: − 0.40, − 0.07; HbA1C: coefficient: -0.21; 95% CI: − 0.39, − 0.03). However, the effect of ACV intake on FPG and HbA1C was independent of the dose of ACV and duration of the study. Furthermore, no association was observed between change in other outcomes of interest following ACV intake and baseline measures, the dose of intervention, and duration of follow-up (Supplemental Table 2).
Sensitivity analysis was performed by excluding individual studies from the meta-analysis. We found that our findings about serum TG was influenced by 3 studies, and when we removed each of these studies from the analysis, the findings did change [excluding Panetta et al. [33] WMD: − 39.38 mg/dL; 95% CI: − 73.18, − 5.59; excluding Mahmoodi et al. [27] WMD: − 39.46 mg/dL; 95% CI: − 75.37, − 3.55; and excluding Khezri et al. [22] WMD: − 20.76 mg/dL; 95% CI: − 36.86, − 4.65]. This was also the case when we removed the study of Bashiri et al. [4] in our analysis on serum HDL-C levels (WMD: 1.68 mg/dL; 95% CI: 0.44, 2.92); such that serum HDL-C levels were significantly increased by ACV consumption. With regards to HbA1C, we found that the study by Mohammadpourhodki et al. [28] had a significant effect on the overall finding; such that after removing that study from the analysis, no significant effect on HbA1C was seen following ACV consumption (− 0.04%; 95% CI -0.18, 0.10).
In addition, when we excluded studies with a high-risk of bias [12, 16, 27, 28], no alterations in findings occurred. Except for the findings of HbA1C, which became non-significant (− 0.03%; 95% CI: − 0.16, 0.10) (Supplemental Figure 1).
Funnel plot showed a slight to moderate asymmetry in some variables (Supplemental Figure 2). Based on Egger’s regression asymmetry and Begg’s rank correlation test, we found no evidence of publication bias in studies on TG, TC, HDL-C, and HbA1C. However, a significant asymmetry was found in studies on serum LDL-C (P = 0.005) and FPG (P = 0.04) according to Egger’s regression test, although, such results were not confirmed by Begg’s rank-correlation test (LDL-C: P = 0.40; FPG: P = 0.17).
The present systematic review and meta-analysis suggested that ACV consumption yielded beneficial effects on serum TC and FPG levels. In addition, a trend toward a significant favorable effect was also observed in serum TG concentrations.
Hyperlipidemia and hyperglycemia are common metabolic disorders that affect many people around the world [34, 36]. In spite of several strategies to manage these abnormalities, lifestyle modifications are the first line of therapy in these conditions. Indeed, findings from the present meta-analysis highlight the application of ACV, as a dietary agent, may be helpful in controlling these metabolic abnormalities [9].
The present study showed that ACV consumption improved serum levels of FPG. With regard to HbA1C, despite the significant overall effect of ACV, we found that the exclusion of one study resulted in a non-significant finding, indicating that the overall findings were study-dependent. The mechanism of the ACV effect on lipid profiles and glycemic related markers has not been well defined; however, empirical studies have suggested several potential mechanisms. Indeed, ACV can improve glycemic status by delaying gastric emptying, enhancing cellular glucose utilization and lipolysis, suppressing hepatic glucose production and lipogenesis, and facilitating insulin secretion [21, 35]. Furthermore, in our study, the beneficial effect of ACV on FPG levels was more pronounced when the duration of studies lasted > 8 weeks. Subgroup analysis revealed that the FPG lowering effect of ACV was not significant in non-diabetic patients. On the other hand, the meta-regression results indicated a negative association between changes in both HbA1C and FPG levels, and their baseline measures. These findings suggest that higher baseline values of FPG and HbA1C might contribute to a greater reduction in these markers following ACV intake.
This study revealed that ACV consumption might reduce serum TC concentrations; where the effect of ACV on lipid profiles might be attributed to its stimulation of acid bile excretion, increasing lipolysis and decreasing lipogenesis [21, 35]. Subgroup analysis indicated a greater beneficial effect on both TC and TG levels among type 2 diabetics patients. In addition, the effect on TG and TC was more notable when interventions lasted > 8 weeks. The results from subgroup analysis also showed a greater lowering effect of ACV on TG and TC levels in doses of ≤15 ml/day. Therefore, 15 ml/day might represent the optimum effective dose of ACV. However, our findings from meta-regression analysis did not indicate an association between the dosage of ACV intake and serum alterations of these parameters. Nevertheless, the null results from meta-regression analysis might be due to the paucity of data in terms of ACV doses in published studies. We also found a significant improvement in HDL-C among non-diabetic participants. Given that diabetic patients are susceptible to higher levels of oxidative stress and the reductions of the expression and/or activity of HDL-C’s anti-oxidative enzymes, such as paraoxonase, in these patients, it is reasonable to expect a higher dosage of ACV would be more effective in these individuals. Therefore, further investigations would be required to shed light on this issue in diabetic patients.
ACV appears to be a safe natural supplement with a functional role in controlling glycemic and lipid profiles. Only two studies [4, 20] had reported some side effects (such as stomach burning and ACV intolerance) following consumption of this supplement. The present systematic review and meta-analysis has some limitations which must be taken into account. The number of included studies, in particular in terms of insulin and HOMA-IR, was relatively low, thereby precluding reliable conclusions to be drawn. Between-study heterogeneity was high for some outcomes, and although we endeavoured to find the source of heterogeneity in subgroup