A major new study has identified a causal signal linking genetically predicted higher instant coffee consumption to a significantly greater odds of developing dry age-related macular degeneration (AMD), the main cause of irreversible sight impairment in the UK.

The research, analysing over 1.1 million GWAS samples across two large-scale cohorts, found that a higher predicted intake of instant coffee was associated with an almost seven-to eight-fold higher odds of developing the condition.

Crucially, the study found no significant statistical association for ground or decaffeinated coffee. The finding isolates a specific risk factor to a specific type of coffee and a specific form of the disease, providing a powerful new piece of the puzzle in eye health.

How the link was uncovered

To investigate the connection, researchers used a powerful statistical method called Mendelian randomisation. This approach uses a person's genetic variations as a proxy for their long-term habits to infer a potential causal relationship.

The method found a strong causal signal between predicted instant coffee intake and dry AMD. However, it's important to note that further analysis did not confirm shared causal genetic variants, which means that other complex genetic factors (a concept known as horizontal pleiotropy) cannot be fully excluded.

The science: why instant coffee is different

The leading theory for this link points to the manufacturing process. The high-heat spray-drying used to create instant coffee elevates acrylamide and measured AGE markers (Advanced Glycation End-products); the full spectrum of AGEs in instant coffee is still poorly quantified.

This mechanism is plausible because the damaging effect of AGEs on the eye is well-documented from laboratory studies. Research has shown that AGEs trigger oxidative stress and inflammation in the retinal pigment epithelium (RPE) - the vital support layer for our light-sensing cells. This cellular damage is thought to contribute to dry AMD progression, although direct human evidence remains indirect.

Understanding dry age-related macular degeneration

AMD is a condition that damages the macula, the small central part of the retina responsible for the sharp, detailed vision we need for reading, driving, and recognising faces.

• Dry AMD is the most common form, accounting for around 90% of cases. It involves the slow thinning of the macula and the build-up of waste deposits called drusen, leading to a gradual but profound loss of central vision.

• Wet AMD is less common but more aggressive, caused by leaky blood vessels. The new study found no link between any type of coffee and wet AMD.

Currently, there is no cure for dry AMD. This makes identifying and mitigating risk factors the single most important tool we have to protect against it.

What this means for you

This study does not prove that drinking instant coffee causes AMD in every person. The finding points to a powerful genetic interaction. It suggests that for individuals who already have a genetic susceptibility to the disease, a higher intake of instant coffee could act as a trigger, dramatically increasing their risk.

As the study's authors explained, this information can be used for a more personalised approach to eye health. Clinicians can advise patients with a high genetic risk to reduce or eliminate instant coffee, offering a precision strategy to lower their chances of developing dry AMD.

For anyone concerned about their long-term eye health, the implications are clear:

• If you have a family history of AMD: A family history is a major risk factor. This study suggests that switching from instant to ground coffee would be a sensible, preventative measure.

• For everyone else: Given that a plausible biological mechanism has been identified, moderating your intake of instant coffee or switching to brewed coffee is a low-cost, evidence-based change you can make to reduce your long-term risk.

While this genetic signal must still be confirmed with direct dietary intervention trials, the research provides a clear and compelling warning that is too strong to ignore.

Sources

• Genetic Correlation and Mendelian Randomization Analyses Support Causal Relationships Between Instant Coffee Consumption and Dry Age-Related Macular Degeneration
• Study shows genetic link between instant coffee consumption and increased risk of dry AMD – Ophthalmology Times
• Studies of acrylamide level in coffee and coffee substitutes – laboratory survey of acrylamide concentrations in instant vs roasted coffee
• AGEs promote oxidative stress and induce apoptosis in retinal pigment epithelium ARPE-19 cells – mechanistic cell-culture work
• RNIB data sheet: Key information and statistics on sight loss in the UK (AMD as leading cause of severe sight-impairment)