The UK is the instant coffee capital of the world, with 54 per cent choosing it over other forms of the hot drink, according to research by Deloitte this year.

But does the cheap and cheerful drink carry a hidden health risk? A study has found a link between drinking instant coffee and age-related macular degeneration (AMD), the leading cause of blindness in the UK which gradually erodes a person’s central vision, making it difficult to do everyday activities such as reading and driving.

There are two forms of AMD – wet and dry. The dry form, which accounts for 90 per cent of the 700,000 AMD cases in the UK, occurs when tiny deposits of protein build up on the macula, the part of the retina that’s responsible for detailed central vision.

With wet AMD, sight loss is due to abnormal blood vessels growing in the back of the eye, damaging the macula.

Some genes are known to raise the risk of AMD – and the study found that when people with these genes drank more than the average consumption of instant coffee (two cups a day), it increased their risk even further. Going from two cups to four increased their risk almost sevenfold.

So should we be getting out our cafetieres, instead? The scientists behind the study suggest so.

The team from Hubei University in China analysed data from more than half a million people in the UK and Finland which included genes, coffee consumption and health status.

They found a ‘significant’ genetic correlation between those who consumed instant coffee and those who developed dry AMD. (No such links were found with other types of coffee or with wet AMD.)

‘Instant coffee may increase the risk of AMD and reducing its intake could help prevent dry AMD,’ wrote the researchers in the journal Food Science and Nutrition.

‘People at risk for AMD should avoid instant coffee. Clinicians can advise patients to reduce instant coffee intake based on genetic risk profiles. These interventions may significantly contribute to AMD prevention and treatment.’

One theory is that the manufacturing process generates high levels of compounds that can damage the retina, researchers said.

As Denise Voon, a clinical adviser at The College of Optometrists, explains, instant coffee is made by brewing concentrated extracts and then spray-drying (where droplets of hot coffee extract are sprayed through hot air to dry them).

‘This process generates higher levels of acrylamide, advanced glycation end-products [when sugar sticks to body components such as proteins, creating a sticky layer] and other by-products that can cause inflammation and other damage to cells in the retina than when manufacturing other types of coffee.’

In other words, it’s not caffeine that’s the problem but by-products of the manufacturing process of instant coffee.

The industrial manufacturing process means instant coffee is an ultra-processed food (UPF), says Sheraz Daya, an eye surgeon at the private Centre for Sight in London.

‘That means it’s produced industrially, using processes such as spray drying,’ he explains. ‘We all know about problems with UPFs, particularly acrylamide which is really toxic.’

A study of more than 150,000 people aged 50-plus, published in the European Journal of Nutrition last year, found that every 10 per cent increase in UPFs in a person’s diet was associated with an 8 per cent increase in their risk of AMD.

A family history of AMD increases your risk – having a parent or sibling with AMD means you have a 50 per cent risk of developing it, too.

‘If I had a relative with a history of macular degeneration, I’d avoid instant coffee – and other UPFs as much as possible,’ adds Mr Daya.

While the study was thorough, it didn’t prove that instant coffee is harmful and it’s important not to panic, says Denise Voon.

Nevertheless, she advises: ‘If you are at particular risk, such as having a first-degree relative with AMD, you may wish to limit your instant coffee intake, or switch to other forms of coffee – and have a rich diet of green, leafy vegetables and oily fish twice a week.’

Yet other experts are more sceptical about the findings. A spokesman for the Macular Society raised questions about the researchers’ methodology, including the decision to combine data from ‘two different countries with very different habits around coffee consumption’.

They added: ‘The statement about stopping instant coffee to stop people developing AMD isn’t backed by robust evidence. AMD is caused by many factors – one single factor, such as drinking instant coffee, is not the cause of AMD.’

Professor Dan Reinstein, an eye surgeon at the London Vision Clinic concurs, saying that while the study makes an ‘eye-catching claim’, the evidence is too weak to suggest that instant coffee damages vision.

It’s possible that the other lifestyle factors, such as smoking and drinking, are behind the link, he says – and not instant coffee at all.

‘There’s no prior reliable evidence that instant coffee harms your eyes,’ explains Professor Reinstein, ‘and this study does not change that.’

He adds: ‘The real ways to protect your sight are to avoid smoking; eat a balanced diet that’s rich in green vegetables and fish; control blood pressure; and get regular eye checks.

‘Coffee choice doesn’t belong on that list.’