Will drinking green tea reduce your risk of heart attacks and strokes?
According to the news headlines, drinking green tea could prevent deaths from heart attacks or strokes. We look behind the headlines.
1 June 2018
A compound found in green tea could help break up plaques that are linked to dangerous blockages, researchers suggest.
The research, part-funded by the BHF, found that a compound in green tea can break up and dissolve potentially dangerous protein plaques found in the blood vessels.
But before you reach for the kettle, it is important to know that to get effective amounts of the compound (called EGCG) into the bloodstream by drinking green tea, you'd need to drink enormous quantities of it - which is not what the researchers are recommending.
The researchers are now looking at other ways that the compound could be used. This could involve changing the chemical structure of EGCG, making it easier to be absorbed from the stomach and more resistant to your metabolism, or developing new methods to deliver the molecule to the plaques – for example via an injection.
The BHF view
Swapping your cuppa for green tea is unlikely to make a big difference with respect to your heart health.
Professor Jeremy Pearson
BHF Associate Medical Director
Professor Jeremy Pearson, Associate Medical Director at the British Heart Foundation, said: “Our bodies are very good at breaking down EGCG, so swapping your cuppa for green tea is unlikely to make a big difference with respect to your heart health.
“But by engineering the molecule slightly, we might be able to make new medicines to treat heart attack and stroke.”
If you want to reduce your risk of heart and circulatory diseases the best way is by adopting a healthy active lifestyle, eating a balanced diet, not smoking, and maintaining a healthy weight, rather than by focusing on a single food or drink.
How was the research carried out?
Atherosclerosis is the build-up of fatty material inside our arteries that can reduce the flow of blood to the heart and brain, and can lead to heart attacks and strokes. In advanced stages of atherosclerosis, a protein called apolipoprotein A-1 (apoA-1) can form amyloid deposits, which are similar in structure to those associated with Alzheimer’s disease. These deposits build up within atherosclerotic plaques. Here, they increase the size of the plaques, further restricting blood flow, and may also make the plaques less stable, increasing the risk of a heart attack or stroke.
The scientists, from Lancaster University and the University of Leeds, have discovered that EGCG, binds to the amyloid fibres of apoA-1. This converts the fibres to smaller soluble molecules that are less likely to be damaging to blood vessels.
The findings can’t be applied to people yet, so we cannot say that drinking green tea is good for you
A weakness of the research is that it was carried out in a laboratory rather than real-life setting. This is as the effect of EGCG could not be demonstrated in humans because the compound is poorly absorbed and quite unstable in the body . While the lab setting means that the results are more reliable as the study can be more carefully controlled, the findings can’t be applied to people yet, so we cannot say that drinking green tea is good for you.
The chemists also carried out a complex process to prepare the green tea, in order to isolate certain compounds from the green tea, which wouldn’t be done at home. A household brand of green tea was added to a small amount of water (40ml, whereas a mug of water is around 350ml). The solution was microwaved for six cycles in total, of either 30 or 15 seconds, with a minute in between, and then filtered twice and freeze-dried until further use.
People who had the flavanol drink had lower blood pressure, lower cholesterol levels and less arterial stiffness than the control group. The study's authors say that this would lead to a lower risk of coronary heart disease, including , and cardiovascular disease.
The media coverage
The research was covered in The Independent, The Guardian and The Mirror.The Guardian’s coverage was good, and make it clear in the first paragraph that the researchers weren’t recommending that everyone drinks green tea to reduce their risk of heart attacks.
The Independent’s story was more sensational, stating that ‘Green tea could hold the key to preventing thousands of deaths each year caused by strokes and heart disease.’ It did acknowledge that more research was needed, but didn’t make it clear that this was research done in test tubes, not in humans, and we can’t say from this research that drinking green tea will have the same effects in the human body.
So is green tea good for me?
Claims have also been made that green tea can help with weight loss, and protection from cancer and Alzheimer’s disease
There have been claims that green tea can help lower your cholesterol and blood pressure. A good-quality review from 2011 found drinking green tea enriched with catechins led to a small reduction in cholesterol.
Similarly, a 2013 review of 11 studies found that having green or black tea daily (either as a drink or capsule) could help lower your cholesterol and blood pressure. But most of the clinical trials they included in this review were short-term, so the authors cautioned that longer term trial were needed to back up their findings.
A 2014 survey of data from previous studies found evidence of a small reduction in blood pressure for people with high blood pressure who consumed green tea. But it is unclear whether this reduction was significant enough to reduce your risk of heart problems or stroke.
Claims have also been made that green tea can help with weight loss, and protection from cancer and Alzheimer’s disease, but there is a lack of evidence to support these claims.