From boosting brain function to helping you live longer, we present 12 reasons for going green.
Medically reviewed by Dr Roger Henderson and words by Annie Hayes
People in ancient China have known about the health benefits of green tea since as far back as 4,000 years ago. To this day, we still enjoy the boiled leaves of Camellia sinensis as a refreshing, warming beverage.
Over the last few decades, the popularity of green tea has increased, and now it can be found almost everywhere – either as dried leaves in teabags, or as matcha in milky lattes.
12 health benefits of green tea
Early green tea studies are promising, though more research is certainly needed. ‘A lot of this research is done in the lab, so the benefits are not definitive, but still interesting,’ says Hobson.
Here’s what we know about the health benefits of green tea:
- Reduces inflammation
Plant compounds called polyphenols are generally what give green tea its health potential, says Hobson. ‘Polyphenols are compounds found in plants which are thought to have many health benefits – one of which is reducing inflammation in the body, which is thought to be at the root of many diseases.’
The main polyphenol in green tea is epigallocatechin gallate (EGCG), which is a catechin. Around 30 per cent of the weight of freshly-picked tea leaves is catchins.
‘The potency of this catechin lies in its function as a powerful antioxidant,’ Hobson explains. ‘This means it can protect your cell from the damage caused by excess free radicals – called oxidative stress – while also suppressing the activity of chemicals that encourage inflammation in the body, such as TNF-alpha.’
- Boosts brain power
Green tea contains caffeine, a known stimulant, ‘but not as much as coffee – which means you can still get a slight stimulating kick but not enough to leave you jittery,’ says Hobson. ‘Caffeine works by blocking adenosine, which is an inhibitory neurotransmitter – this then leads to an increase in energy. Caffeine has been shown in many studies to help boost brain function, including mood and memory, so there is a benefit as long as you don’t overdo it.’
‘Caffeine is thought to help with memory and alertness, while L-theanine helps to settle an overactive brain by way of GABA.’
The other compound in green tea is L-theanine, an amino acid often associated with relaxation. ‘This amino acid can cross the blood brain barrier, where it increases the activity of GABA – an inhibitory neurotransmitter that helps to quell activity in the brain, hence its association with relaxation and links to anxiety,’ Hobson explains.
Research shows that L-theanine increases dopamine and alpha waves in the brain, he continues, which is thought to relax the brain without inducing drowsiness. Combining caffeine and L-theanine is thought to have a particularly powerful effect on improvement in brain function, Hobson adds. ‘Caffeine is thought to help with memory and alertness, while L-theanine helps to settle an overactive brain by way of GABA.’
- Protects against brain-ageing
Not only can drinking green tea boost your brain function, but it may also protect your brain as you age. Several studies have shown that certain compounds in green tea have neuroprotective properties.
‘This research is lab (test tube) and animal-based, but suggests that the catechins in green tea may help to protect neurons in the brain, which has potential for lowering the risk of dementia,’ says Hobson.
- Assists with weight loss
There’s far more to weight loss than simply drinking a cup of green tea each day, but the drink could complement your efforts. Some research indicates that green tea can help to increase fat burning and boost your metabolic rate.
‘It has been suggested that green tea helps to convert some of the fat stored in the body into free fatty acids, and so increases fat burning,’ says Hobson. ‘More realistically, the caffeine in the tea could help to increase performance. If you train harder you burn more calories, I guess.’
- Boosts endurance exercise
The science on this one is mixed. A rodent study by the American Physiology Society that tested the effect of regularly taking green tea extract (GTE) found that over 10 weeks, endurance exercise performance was boosted up to 24 per cent with an extract supplement that was equivalent to drinking four cups of tea per day.
However, there is no evidence that green tea could induce any athletic benefit in humans. In fact, it may even have the opposite intended effect. ‘Some say that green tea may not be a good thing for endurance athletes as it can impair adaptations to endurance exercise and decrease carb absorption in sports people such as runners and cyclists,’ says Hobson.
- Reduces bad breath
Despite its bitter taste, green tea may also be good for your oral health. This appears to be due to its high catechin content. Test-tube studies suggest that catechins can inhibit the growth of oral bacteria.
‘Research suggests that they may help to reduce the growth of bacteria that can cause a build-up of plaque, leading to tooth decay and bad breath,’ says Hobson. ‘Only a little bit of research linking this to green tea itself, as most is centred around the catechins in isolation.’
- Protects against heart disease
Your morning brew may also be heart-healthy, too. ‘Research has linked green tea consumption to an improvement in some of the risk factors for heart disease,’ says Hobson. ‘This includes lowering total cholesterol and LDL ‘bad’ cholesterol levels. Green tea may also protect LDL from oxidation, which is a crucial step in the development of heart disease.
A study by the European Society of Cardiology found that the consumption of green tea rapidly improves the function of endothelial cells lining the circulatory system, with a peak increase of 3.9 per cent just 30 minutes after consumption. Endothelial dysfunction can cause arteries become clogged with fatty substances (known as atherosclerosis).
- May protect against cancer
There is research to suggest that green tea drinkers are less likely to develop certain cancers – including breast, prostate and colorectal – but this doesn’t mean drinking green tea will prevent you from getting cancer, says Hobson. ‘This protective effect is thought to be a result of the antioxidant potency of green tea,’ he explains.
Laboratory studies have shown that the catechins in green tea inhibit cancer cell growth, motility and invasion, and stimulate cancer cell death. Green tea catechins also prevent and reduce tumor growth in animal models. While this research is certainly interesting, robust human studies are needed before any conclusions can be drawn.
- Boosts immune system
Making green tea your go-to brew could give your immune system a boost, thanks to one of the beneficial plants compounds in green tea – the polyphenol EGCG. ‘Research has suggested that EGCG found in green tea may support immunity by way of its powerful ability to increase the number of T-cells, which play a key role in immune function and suppression of autoimmune disease,’ says Hobson.
- Improves bone health
Test tube studies have shown that green tea contains a group of chemicals that stimulate bone formation and help slow its breakdown. ‘The active components of green tea may benefit bones by promoting an increase in osteoblast – cells that form new bone – numbers and activity,’ explains Hobson.
In an Oregon State University study, scientists exposed a group of bone-forming cells to three major green tea components – epigallocatechin (EGC), gallocatechin (GC), and gallocatechin gallate (GCG) – for several days. They found that EGC boosted the activity of a key enzyme that promotes bone growth by up to 79 per cent. Additionally, high concentrations of ECG blocked the activity of a type of cell that weakens bones.
- Helps you live longer
Drinking green tea could even add years to your life, observational studies show. ‘This is really interesting,’ says Hobson. ‘A large study of Japanese adults over 11 years showed that those who drank the most green tea had a significantly lower chance of dying during the study period.’ Among those who consumed five cups of tea per day, death from all causes was 12 per cent lower in men, and 23 per cent lower in women.
Allergy sufferers, take note. Researchers have identified a compound in green tea that blocks a key cell receptor involved in producing an allergic response. In American Chemical Society lab tests, EGCG was shown to essentially block the production of histamine and immunoglobulin E (IgE) – two compounds in the body are involved in triggering and sustaining allergic reactions. Although promising against allergies, no one knows how much green tea is needed to have a therapeutic effect, or which green tea varieties work best, the researchers said.