Feeling peckish one day in 2017, Darshna Yagnik, an immunologist and lecturer in biomedical science at Middlesex University, took a punt on something that had been lurking at the back of the fridge. She soon regretted it and started feeling queasy. Desperate to avoid food poisoning, she racked her brains for something that might help – and remembered the bottle of apple cider vinegar (ACV) in the cupboard. She decided to glug a diluted shot. “Immediately, I felt like there was something going on, combating the bacteria,” she says. “My stomach was gurgling and after about 10 minutes it started feeling soothed. After about half an hour or an hour, I felt much better.”

At that moment, she realised she was using her own body for research. “I was thinking: what is going on with this apple cider vinegar? This is possibly having an effect on E coli. Let me test it in the laboratory.” She went on to do “a multitude of experiments” throughout the pandemic, resulting in a 2021 paper demonstrating that ACV kills E coli and MRSA in petri dishes almost as effectively as common antibiotics. However, it is not clear how this would translate to the human body.

Nonetheless, this is one of the many promising results in recent studies into the benefits of ACV, once the preserve of health-food-shop aficionados. It is said to help normalise blood-sugar levels, reduce inflammation, aid weight loss and improve cholesterol levels. Even before the research, its popularity as a folk cure-all was growing quietly, but it is now being touted by health influencers as a quick fix for gut health.

Deep down, of course, we all know that there are no quick fixes when it comes to health. A few swigs of vinegar can’t counter a sedentary lifestyle spent munching ultra-processed foods.

Nevertheless, research into some of the health claims made for the fermented apple juice is promising, but without large, robust clinical trials, medical staff can’t countenance recommending the stuff. Nichola Ludlam-Raine, a registered dietitian, says that while ACV has a reputation for aiding digestion, “there is no evidence supporting that”. However, organic, unfiltered ACV is probiotic, she points out, as long as there is a brown, blobby fog called “the mother” floating around in it. This, she says, “includes different proteins, enzymes and bacteria. Some people believe that this is responsible for the health benefits of consuming apple cider vinegar, although there are no studies documenting this.”

ACV also contains 5% to 6% acetic acid, says Ludlam-Raine. “Some believe this plays a key part in the health claims. Acetic acid is found in most fruits, which are also key sources of vitamins, minerals and fibre – unlike apple cider vinegar.”

With Yagnik’s work, too, much more research is needed before the vinegar can be recommended officially for fighting pathogens, but what she has found so far is compelling. “I started researching different ways the vinegar might be acting on the bacteria,” she says. “I wasn’t surprised at the results, but it was amazing how it was working – it just destroyed them. Even my microbiologist friends were amazed.”

Handily, so far, it seems only to kill nasty bugs. “It has different effects on different microbes,” she says. “The effects seem to vary according to the microbe type, whether it is E coli or candida.”

Yagnik also doused white blood cells in ACV. Lo and behold, they were able to clear infections much more quickly than normal, “so it seems to be working on immunity as well”, she says. Her hypothesis may explain why so many people claim anecdotally that ACV makes them feel better in general (although this could be the placebo effect): “Vinegar that contains the mother has enzymes and antioxidants that support cell metabolism and function ... It’s high in flavonoids and beneficial bacteria, which contribute to the human microbiome – vital for cellular immunity and defence.”

In a nutshell, she is suggesting that ACV has a two-pronged approach to fighting bugs: killing the bugs and strengthening our cellular defences. That said, the effects always depend on the individual, she says: “Everyone’s got a different immunity.”

While studying the effects on cells, she saw signs that ACV could help reduce inflammation, too. Again, Yagnik suspects this is due to many components working together, from the enzymes to the flavonoids. “All of these in combination would optimise cells, boosting their function, and bring immune balance.”

The evidence on ACV controlling blood sugar is also intriguing. A 2019 meta-analysis of six small studies found that taking it daily resulted in lower fasting blood-glucose levels, as well as reduced cholesterol. A study in 2004 of people with insulin resistance or type 2 diabetes found that taking ACV after a high-carb meal reduced blood-sugar spikes (regular blood-sugar spikes and subsequent crashes are associated with chronic disease).

This means that it could be helpful, alongside medication, in controlling blood sugar for people with type 2 diabetes. At present, however, it is not medically recommended and could cause problems in blood-sugar control for people with type 1 diabetes.

The cholesterol finding from one of the blood-sugar studies is backed up by a meta-analysis of nine trials, which concludes that taking one tablespoon of ACV daily is most effective after doing so for eight weeks or more.

While the weight-loss studies are small and inconsistent, and give only a short-term picture, one found that, with two groups on a calorie-controlled diet for 12 weeks, the half that also took 30ml of vinegar every day lost on average 1.5kg more. Another found that overweight participants lost 1kg to 2kg over 12 weeks with no dietary restrictions. But all of these results should be interpreted with caution.

“Drinking apple cider vinegar should not replace medicines for diabetes management and could be bad news for teeth health,” says Ludlam-Raine. “Apple cider vinegar is strongly acidic, so there are risks of enamel erosion – and reflux [heartburn], too.”

There have also been warnings that people with kidney disease or ulcers should avoid such acidity. Ludlam-Raine says: “Evidence is minimal at present regarding appetite suppression and improving blood-sugar levels following a high-carb meal. You’re better off eating an apple (there’s more fibre, to keep gut bacteria happy, and it contains antioxidants, too).

“However, if you want to include AVC in your diet, use it in a salad dressing – alongside olive oil and black pepper – rather than drinking it.”

Of course, it is up to individuals whether they want to experiment on themselves with ACV. The key is to know the risks, to keep exercising and to eat a varied diet.

Yagnik – along with many others – now swears by a daily dose of ACV. “I carry it around with me in a small bottle,” she says, in case she feels suddenly as though she is coming down with an infection. “I just feel better with it. I think it’s really important to have the right nutrition and to boost your immunity, because of what we’ve seen with the pandemic – it has affected a lot of people’s immunity.”

She dilutes it one to one with water or juice and takes it after a meal, “so I’m not absorbing it on an empty stomach. Because some people might feel a little bit sick.”

Since her first study, Yagnik has started testing ACV’s impact on healthy people and those with infections; she says her findings show that “it does help clear infections, with no side-effects” – unless you count not enjoying the strong taste.

Informally, too, since her lab experiments, friends, family and colleagues have started taking it. “And they haven’t stopped. They just take it routinely, like a supplement, every day, because they feel the health benefits,” she says.

She concedes that much more research needs to be done; her own work continues. “There are so many different pathways that it’s acting on and it’s very exciting,” she says. “I think we’ve only scratched the surface.”