People all over the world have been drinking tea for centuries, and for many good reasons. A growing field of research is showing how tea has a role to play in reducing the risk of many chronic diseases. And on top of that, a good cup of tea has a real calming and relaxing effect – just what we need in these stressful times. So put the kettle on, sit back, and relax, as I explore the health benefits of tea.
After water, tea is the most popular beverage in the world. Since ancient times, tea drinking has been considered a healthy habit. Now modern medical research is providing a scientific basis for this belief. While some tea brews provide more health advantages than others, there’s plenty of evidence that regularly drinking tea can have a lasting impact on your health. It is the beneficial bioactive compounds found in tea that are linked to reducing the risk of developing chronic diseases such as heart disease, diabetes, some forms of cancer and even improving your mental health.
Types of tea
First, let’s set the scene. For this article, when I refer to tea, I’m specifically referring to the main varieties that came from the plant Camellia sinensis. From this plant comes most of the popular brews including black tea, green tea, white tea and oolong tea. There is a misconception that herbal tea is also tea. However, herbal tea is not made from the plant Camellia sinensis and instead is made from infusions of various herbs and spices like chamomile and peppermint, so I won’t be touching on those types of teas. I’ll just stick to traditional tea and its common varieties.
What makes tea so interesting from a health perspective is its unique mix of a family of bioactive compounds called polyphenols. Two, in particular, called catechins and theaflavins, are the main polyphenolic compounds in tea and are thought to be responsible for most of the physiologic effects of tea. There is also some caffeine in tea. Not as much as coffee, but there enough there to give some level of mental effect.
Black, green and oolong tea all come from the same plant, but each has its own unique flavour profiles. The different flavours and colours come from how tea is processed after picking. Oolong and black teas are oxidised or fermented, so they have lower concentrations of polyphenols than green tea, but the levels are still considered high.
For green tea, tea leaves are harvested then quickly heated and dried to prevent too much oxidation and fermentation from occurring. This needs to be done quickly otherwise the green leaves would turn brown and lose their fresh-picked flavour.
For black tea, tea leaves are exposed to air to allow them to ferment for several hours by natural enzymes found in the leaf. This oxidation process turns the leaves a deep-brown colour and during this process, the flavour is intensified. The leaves are then left as such or are heated, dried and crushed. Black tea has the highest content of caffeine of the different tea varieties but is still much less than a regular cup of coffee.
Oolong tea is produced by partial oxidation of the tea leaf so sits between the processes used to make green and black tea. Because oolong tea is neither a black tea nor a green tea, it can end up with more black tea characteristics or more green tea characteristics depending on the direction the tea master takes in the processing of the tea.
Polyphenols and health
Those polyphenols that I mentioned before are the stars of the show when it comes to the health benefits of tea. A brief reading about tea on the Internet will bring up article after article highlighting its polyphenol content and because polyphenols are antioxidants, that explains the health benefits of tea. Just no. Polyphenols are much more than antioxidants. It should instead be about polyphenols and their multitude of benefits and actions in the body such as:
- Regulating cell growth and death
- Slowing down cancer cell proliferation
- Altering glucose responses and insulin sensitivity
- Increasing activity of enzymes involved in removing harmful substances from the body
- Decreasing inflammation
And to show how complex it all is, our gut microbiota is also involved in the metabolism of polyphenols in tea. A recent review of the research field shows the promise that tea offers in favourably changing the diversity of the gut microbiome. So, a healthy gut microbiome may even help augment the function of polyphenols. See how simplistic it is to just talk about “tea being full of antioxidants and….health!”
A question I’m often asked is whether putting milk in tea will block the absorption of all those beneficial polyphenols. While it was thought in the past that it would do this, current expert opinion is that the effect is negligible. Drink your tea how you like it.
Tea drinkers may be helping to keep their hearts healthy with a meta-analysis from 2019 finding a reduced risk of cardiovascular disease in people who regularly drink tea. Although the findings have been mixed in terms of tea’s effect on lowering cholesterol and blood pressure. It seems that tea can reduce low-density lipoprotein (LDL) cholesterol that can build up in arteries while at the same time increasing the more beneficial high-density lipoprotein (HDL) cholesterol which helps to remove excess cholesterol from the blood.
Several studies have shown that tea may favourably alter glucose metabolism and insulin signalling, which has spurred interest in the health effects of tea consumption in diabetes. Some studies suggest that it is the polyphenol catechins in green tea that may help to keep blood sugar in check, reducing the risk for developing type 2 diabetes. A 2014 meta-analysis of 15 published studies involving more than 545,000 participants found an inverse relationship between tea consumption and the risk of developing type 2 diabetes. For each additional two cups of tea drunk every day, the risk of developing diabetes dropped by almost 5 percent.
Though there is lots of information online about tea as a cancer-fighting beverage, research has not proven that consuming tea helps to reduce the risk of cancer. Some studies suggest that tea drinkers have a lower risk for certain types of cancer, but other studies do not support these findings. At this time, it is unknown if tea drinking can reduce the risk of cancer. If we look at what the World Cancer Research Fund has to say about it, there is only limited suggestive evidence that tea may help lower the risk of bladder cancer, and its crickets for most other forms of cancer.
And following on from the findings of the World Cancer Research Fund, a Cochrane systematic review looked at associations between green tea and the risk of cancer. The review included 51 studies containing more than 1.6 million participants. There was insufficient and conflicting evidence to give any firm recommendations regarding green tea consumption for cancer prevention.
Can tea keep you slim?
And next, we have the claims made about tea being just the tonic to help you lose weight. Well, not all kinds of tea, specifically green tea. Green tea is believed to be able to increase a person’s energy output which could help with weight loss. Many of the commercial green tea weight loss preparations contain higher concentrations of ingredients (specifically catechins and caffeine) than a typical green tea beverage prepared from leaves. That means it is green tea extract supplements that are studied in clinical trials, not the beverage.
So, does popping a green tea pill help someone lose weight? Many clinical trials have been carried out with different findings from each of them. Combining all the research together was the goal of a Cochrane Review. The review looked at 15 weight-loss studies of around 3 months duration each, along with three studies looking at weight maintenance. Each study involved some form of a green tea preparation given to one group with the results compared to a group receiving a placebo pill.
The clear conclusion from the review was that weight loss in people who took a green tea supplement was not statistically different from people taking a placebo. The absolute amount of weight loss seen was very small and was not likely to be clinically important. Studies examining the effect of green tea preparations on weight maintenance did not show any benefit either compared to the use of a placebo. If green tea is a true weight-loss miracle, then most of the miracle will be because a person believes it works and adjusts their eating and activity habits accordingly. That’s it.
Tea and mental health
Tea has long been considered beneficial for mental health, especially for its ability to calm and relax. One recent health condition being associated with tea consumption is depression. Tea, especially green tea, is thought to have a beneficial effect on the prevention and management of depression due to its anti-inflammatory properties. Inflammation is part of the body’s response to stress and as such is thought to affect the production and function of neurotransmitters associated with depression symptoms. Green tea also contains large amounts of an amino acid called theanine which has been shown in laboratory studies to have a relaxing effect on the brain by increasing serotonin and dopamine production so that can help with mental health too.
So, what does the research say about tea and depression? A meta-analysis published in 2016 that included 11 studies involving almost 23,000 participants found that for every three cups of tea consumed per day, the relative risk of depression decreased 37 percent. It seems then that regular drinkers of tea do appear to have lower rates of depression. More definitive research is needed to be able to state with some conviction that the link is a direct one in that it is the tea itself helping to improve mental health. Until such research findings are in, sit back and enjoy a relaxing cup of tea or two.
And adding to the mental health benefits of tea, new research has found that regular tea drinkers have better organised and better functioning brains. With regular tea drinkers observed to have a reduced risk of cognitive decline and a plausible mechanism to explain it, researchers are homing in further to see just how much of a health benefit a daily cuppa can provide.
To look at the brain effects of tea, a research team recruited 36 healthy adults aged 60 years and above. Each person undertook a battery of psychological tests as well as a MRI scan of their brain. The MRI scanning results showed that people who drank green, black or oolong tea at least four times per week over many years had a more efficient structural organisation of their brain. What this means is that brain regions were connected more efficiently. Think of it like car traffic flow where a well-designed road system allows cars to get where they need to as quickly and efficiently as possible. While the results are still observational so cannot prove it is the tea drinking being the main cause of this, it does provide more evidence to support the brain health benefits from a daily cup of tea.
What it all means
At the end of all of this, there are lots of health benefits to drinking tea. But to be honest, when I look at the total research related to tea and compare that to the quantity and quality of research to do with coffee (which I’ve blogged about here), I would have to say that coffee seems to be in front. But it is all a moot point in comparing tea to coffee. They’re both great beverages. If you enjoy coffee, keep drinking it. And if you enjoy tea then just keep drinking it, and carry on.