Apple cider vinegar: what is the evidence?
Miracle ingredient or harmful to health? We put apple cider vinegar to the test.
Few ingredients have been as hyped as apple cider vinegar. Scarlett Johansson claims that washing her face with diluted apple cider vinegar keeps her skin clear; the explorer Sir Ranulph Fiennes swears by it, claiming he beat his arthritis thanks to a regular vinegary drink (four parts apple cider vinegar to one-part raw honey). So which of its health benefits, if any, have evidence to support them?
Claim: Apple cider vinegar can bring down your blood sugar
Verdict: Correct, but likely to be true for all vinegars
As part of the BBC TV series, ‘Trust Me I’m a Doctor’, we teamed up with Dr James Brown from Aston University to find out whether apple cider vinegar could live up to the claim, often made, that it can help to bring down your blood sugar.
We started by recruiting some healthy volunteers and asking them to eat two bagels. We measured their blood sugar levels before and after eating and, as expected, bagel consumption was followed by a large and rapid rise in their blood sugar levels.
The next day we asked them to consume another two bagels, but this time we asked them to knock back a diluted shot of apple cider vinegar just before doing so. Finally, we repeated the test a few days later, but this time we got our brave volunteers to gulp down some dilute malt vinegar before the bagel.
It turned out that the apple cider vinegar, but not the malt vinegar, had a big impact, reducing the amount of sugar going into our volunteers’ blood by 36 per cent.
Our small experiment reproduces the findings of a substantial number of studies pointing towards the ability of vinegar to reduce carbohydrate load. Researchers in Sweden1, for example, found that when healthy volunteers ate a test meal of bread, butter and yoghurt, substituting a vinegar-pickled cucumber for a plain cucumber lowered the GI of the meal by a whopping 30%.
One explanation for this could be that the acetic acid in vinegar has, in tests, been shown to suppress the activity of enzymes that normally break down starches and complex sugars, slowing down the rate at which the sugar gets absorbed.
Vinegars can vary in the level of acetic acid that they contain, which might go some way to accounting for the greater impact on blood sugar, in our experiment, of the apple cider vinegar compared to malt vinegar.
Reviewing the body of scientific evidence overall, we can confidently state that consuming vinegar with meals can help reduce blood sugar after eating.
Claim: Apple cider vinegar can bring down your cholesterol
Following on from our successful bagel trial, we devised a more extended test to measure apple cider vinegar against four further claims made for it: that it can help with weight loss, reduce inflammation, and bring down cholesterol.
We recruited 30 volunteers and divided them into two groups. For eight weeks, the first group had to consume two tablespoonfuls of apple cider vinegar diluted in 200 ml water before lunch and dinner. We asked the second group to do the same with malt vinegar and the final group got a placebo of coloured water.
Two months later, we tested their weight, blood levels of CRP (a marker that doctors use to measure inflammation), and blood fats.
None of our test group lost any weight, and although some of the volunteers consuming apple cider vinegar did see falls in their CRP levels, the numbers were not large enough to be statistically significant.
When we looked at blood lipids (blood fats), however, we saw a marked improvement in the apple cider vinegar group alone: a reduction of fully 13% in total cholesterol, with a particularly big reduction in triglycerides (a form of fat closely linked to cardiovascular disease).
This was particularly striking because our volunteers were all healthy at the start, with relatively normal cholesterol levels. Dr Brown was surprised and pleased by this result. “Bringing cholesterol levels down”, he commented, “even by a small amount like ten per cent, can significantly reduce your chances of having a heart attack in the future. So we were really excited to see that finding.”
An increasing body of research2 3 4 suggests that the effect of apple cider vinegar on blood fats is likely due to its antioxidant properties, being rich in a family of plant-based substances, known as polyphenols.
Claim: Apple cider vinegar can benefit your microbiome
Verdict: Probably true
Apple cider vinegar is produced using a two-step process. First, yeasts and bacteria ferment the natural food sugars present in apple juice to produce alcohol. Whilst acetic acid bacteria convert most of the alcohol into vinegar.
The accumulated yeast and bacteria form a cloudy substance known as “mother of the vinegar”, or “mother” for short. Laboratory tests on “mother” have shown that it contains a wide variety of probiotics, including lactobacillus, which is well-known for its role in promoting a healthy gut biome, and oenococcus, which has been found to have anti-inflammatory effects. In unfiltered and unpasteurized apple cider vinegar, the “mother” remains fully bioactive, and organic apple cider vinegar has the widest microbial range of all.
There are, at present, no published experimental studies assessing the benefits of apple cider vinegar on the human gut microbiome. However, linking the established evidence showing that probiotics can benefit gut health together with the evidence that they are present in apple cider vinegar, it is likely to lead to a happier, healthier gut.
Are there any risks to consuming apple cider vinegar?
Verdict: Yes, if you overdo it
Before you stock up, you might want to check: can apple cider vinegar cause harm? The case of a 28-year-old Austrian woman suggests that when consumed to excess, it can. After about six years of drinking a quarter of a litre of apple cider vinegar (neat) each day, she fell ill. Medical tests showed that the repeated high doses of acid had wreaked havoc upon her body, depleting her body of potassium, and leaching calcium from her bones.5
The body is not well-adapted to consuming large doses of undiluted acid, and has to send the kidneys into overtime to bring body pH back to a safe level. This, in turn, causes the loss of key minerals suffered by the woman in the case study. Vinegar consumed straight, on a regular basis will, may also damage tooth enamel. Although well-diluted apple cider vinegar is harmless from this point of view, people with impaired kidney function in particular should avoid drinking it neat.
So, what is the verdict?
Evidence points to some health benefits in apple cider vinegar. In common with all vinegars, it can lower blood sugar after meals. Uniquely however, anti-inflammatory plant compounds present in apple cider vinegar can also bring down blood fats. Tests have also shown the presence in apple cider vinegar of microbes known to be beneficial to gut health.
However, as it is an acid, it is best to consume it in dilute form and in moderation; probably no more than 1 medium sized glass diluted a day, usually before a meal.
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1Ostman, Granfeldt et al – ‘Vinegar supplementation lowers glucose and insulin responses and increases satiety after a bread meal in healthy subjects’ https://www.ncbi.nlm.nih.gov/pubmed/16015276
2Halima, Sonia et al, ‘Apple Cider Vinegar Attenuates Oxidative Stress and Reduces the Risk of Obesity in High-Fat-Fed Male Wistar Rats’, https://www.ncbi.nlm.nih.gov/pubmed/29091513
3Naziroglu, Güler et al, ‘Apple cider vinegar modulates serum lipid profile, erythrocyte, kidney, and liver membrane oxidative stress in ovariectomized mice fed high cholesterol’, https://www.ncbi.nlm.nih.gov/pubmed/24894721
4Budak, Kumbul et al, ‘Effects of apple cider vinegars produced with different techniques on blood lipids in high-cholesterol-fed rats’, https://www.ncbi.nlm.nih.gov/pubmed/21561165
5Lhotta, Höfle et al, Hypokalemia, hyperreninemia and osteoporosis in a patient ingesting large amounts of cider vinegar. https://www.ncbi.nlm.nih.gov/pubmed/9736833 [referenced in Johnston & Gaas, ‘Vinegar: Medicinal Uses and Antiglycemic Effect’, https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1785201/#R53