KOMBUCHA, A FERMENTED, slightly effervescent tea, has been consumed for more than 2,000 years. It is likely to have originated in Northeast China.

Hailed for its health benefits, it quickly became popular across Asia before eventually making its way to Europe in the early 20th century. It took another century for it to be discovered by Hollywood.

Touted by celebrities such as Gwyneth Paltrow on the pages of Goop and Kourtney Kardashian’s on Poosh, its popularity has exploded in the last decade.

Health claims include its ability to protect against inflammation, lower cholesterol and blood pressure, slow cancer growth and boost the immune system.

But is any of this actually true?

Many of the claims come from animal studies – so far, the evidence from human studies is limited.

Here’s what we know so far…

Kombucha is a fermented drink made from tea (either black or green), water, sugar and something called a SCOBY, which is a disc-shaped symbiotic culture of bacteria and yeast.

Ingredients such as lavender, ginger, blueberry, or lemon can be added for a variety of flavours.

Kombucha is made by steeping in tea in boiling water and adding sugar. After the sweetened tea is cooled, the SCOBY is added. The yeast in the SCOBY reacts with the sugar in the tea, fermenting the mixture. It then ferments at room temperature for several days, or until it reaches the desired flavour and chemical properties.

The Kombucha SCOBY, which generates the bacteria changes. Alamy Stock Photo Alamy Stock Photo

After the addition of flavours, it is bottled and continues to ferment for another couple of weeks. This allows the bottle to trap the carbon dioxide produced in fermentation, carbonating the drink.

Health benefits

Fermented foods such as yoghurts, sauerkraut and kefir all contain live microorganisms. One of the by-products of fermentation is acetic acid. It is thought that this, as well as other compounds found in green and black tea, may suppress the growth of less desirable bacteria and yeast whilst promoting more beneficial strains.

At certain concentrations, these probiotic microbes can help to balance levels of bacteria in the gut and improve digestion. However, so far there have not been enough studies to confirm whether kombucha contains enough of these beneficial bacteria to be classified as an effective probiotic. The amount and strains of probiotic microbes can also vary depending on factors such as how the kombucha was made and the fermentation time.

A review in the American Journal of Gastroenterology (2014) combined the results of more than 20 studies and found that probiotics, such as the ones found in kombucha, might help to relieve the symptoms of Irritable Bowel Syndrome. However, the quality of the evidence was low.

Homemade fermented kombucha. Alamy Stock Photo Alamy Stock Photo

A study published in Nature (2021) linked consumption of kombucha with anti-ageing and anti-inflammatory benefits, as well as promoting a healthy skin microbiome, which are the organisms that live on your skin and play an important part in maintaining health.

One recent review of animal studies published in Critical Review of Food Science and Nutrition (2023) combined the results of 15 studies and suggested that drinking kombucha was linked to slowed inflammation, improved liver function and the promotion of a healthy gut. The researchers also suggested that kombucha might be helpful in the management of obesity. Further research is needed to substantiate these claims.

A paper in BMC Complementary Alternative Medicine (2012) based on animal studies suggested that kombucha may have health benefits in terms of promoting healthy cholesterol levels. Further research published by Cambridge University Press (2017) linked drinking kombucha to slowing the progress of cancer, protecting against heart disease and neurodegenerative diseases such as Alzheimer’s.

However, while these studies cannot be discounted, it is not known whether results in animal studies would translate to similar results in humans.

What is known is that kombucha is loaded with antioxidants and polyphenols that work overtime to protect your body from damage.

Alamy Stock Photo Alamy Stock Photo

Antioxidants are substances that protect the body from the oxidative damage caused by free radicals. Free radicals are a normal by-product of processes in the body, but the key is to minimise their impact by consuming food and drink rich in antioxidants.

Tea, especially green tea, is rich in a group of antioxidants called polyphenols, especially catechins. They act by limiting inflammation that is the precursor of health issues such as heart disease, cancer and arthritis.

However, there are a number of factors that can influence the antioxidant properties of kombucha, including the tea it was made from and the fermentation time.

Kombucha also contains small amounts of vitamins and minerals, which are produced when the yeast breaks down the sugars, including Vitamin C and B vitamins such as B1, B6 and B12, although levels are likely to vary between products.

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A paper in Nutrients (2018) highlighted results from laboratory studies suggesting that kombucha may play a role in controlling blood sugar. However, the different varieties of kombucha on the market vary in their sugar content, and some products with a higher sugar content could lead to spikes in blood sugar.

Is kombucha safe for everyone?

Kombucha is classified as a functional food because of its potentially beneficial effects when enjoyed as part of a varied and balanced diet. However, it may not be suitable for everyone, and there may be some risks.

Kombucha contains small amounts of alcohol, secondary to the fermentation process so that people with liver problems or those who are pregnant or breastfeeding, as well as those who have a compromised immune system, may want to talk to a health professional before drinking it.

It is important to highlight that there have not been many clinical studies to prove its safety and efficacy. There have been reports that drinking too much can lead to unpleasant side effects like nausea, dizziness or stomach pains. Prolonged fermentation in home brews can lead to the accumulation of organic acids, which might reach harmful levels.

Commercially produced kombucha is subject to strict health regulations. However, preparing kombucha incorrectly has the potential to let harmful bacteria and moulds contaminate the process, which could lead to illness.

Kombucha is now mass-produced, with some products better than others. Alamy Stock Photo Alamy Stock Photo

Fermented foods, including kombucha, are high in histamine, so those with a histamine intolerance should be aware that consuming kombucha may exacerbate symptoms.

A study published by the Centres for Disease Control (1995) suggested that drinking up to 4 ounces of kombucha per day is probably safe for a healthy adult. Note that most kombucha bottles sold in shops are more than 4 oz. If you are new to kombucha, it’s best to start slow.

Always check with your GP if you are concerned about introducing kombucha to your diet, or if you have any adverse side effects after consuming it.

Limiting the portion size will also help to keep added sugars in check. Check the nutrition label for ‘added sugar’ content, keeping in mind that 4 grams of added sugar equals 1 teaspoon of sugar.

Kombucha has a lot of potential health advantages. Is there an abundance of research to support the widespread health claims? The answer is not yet, but it is hard to argue against there being some benefit.

Dr Catherine Conlon is a public health doctor in Cork.