Instant coffee may damage your eyes, genetic study finds

A new genetic study shows that just one extra cup of instant coffee a day could significantly increase your risk of developing dry AMD, shedding fresh light on how our daily beverage choices may shape long-term eye health.

In a recent study published in the journal Food Science & Nutrition, researchers utilized an extensive genomic dataset comprising more than 500,000 individuals, along with advanced genetic correlation and Mendelian randomization analyses, to investigate the causal associations between coffee consumption and the risk of age-related macular degeneration (AMD).

Study findings revealed a statistically significant genetic causal association between instant coffee intake and the subsequent risk of dry AMD. In contrast, ground coffee and decaffeinated coffee demonstrated no such associations, highlighting that based on this research, adverse coffee-AMD links appear to be exclusive to instant coffee. The study found that each standard deviation increase in instant coffee consumption corresponded to a substantially increased risk of the disease.

Background

Age-related macular degeneration (AMD) is an ocular disease characterized by damage to the macula, resulting in blurry vision that progressively deteriorates. AMD is the leading cause of vision loss among older people worldwide, estimated to impact 8.7% of adults (196 million cases in 2020). As the global population ages, AMD prevalence is expected to surge in the coming decades (~240 million cases by 2040).

While recent genetic research has identified several correlations between individual genotypes (susceptibility genes) and AMD development, the disease’s underlying mechanisms and modifiable risk factors (health behaviors like diet and physical activity) remain comparatively understudied. While dietary supplements and clinical interventions (e.g., laser treatment) can slow AMD progression, the condition is irreversible, underscoring the need for prevention-focused research and policy.

While only a handful of epidemiological studies have investigated the role of coffee, one of the world’s most popular beverages, in the pathology of AMD, they report mixed and sometimes conflicting results. Most of these investigations are cohort studies and are therefore vulnerable to biases (e.g., reverse causation, confounding factors), which limits their clinical reliability. Furthermore, none of these studies have differentiated between coffee subtypes (decaffeinated, ground, or instant).

About the study

Biobank & Finngen) in tandem with genetic correlation and Mendelian randomization (MR) analyses to establish causal associations between different forms of coffee consumption and subsequently AMD risk.

Coffee consumption data were obtained from the UK Biobank GWAS summary statistics, including type (total coffee, n = 105,037; decaffeinated, n = 62,072; ground, n = 72,276; or instant, n = 180,764) and amount of coffee intake. AMD data were obtained from the Finngen GWAS dataset, including wet AMD (case = 5,890, control = 300,152) and dry AMD (case = 7,589, control = 298,486). The study’s Mendelian Randomization approach used genetic variants as a proxy for coffee intake, a method that inherently minimizes the influence of traditional confounding factors like diet and lifestyle. This approach relies on key assumptions, including that the selected genetic variants influence AMD only through their effect on coffee consumption and not through other biological pathways (a concept known as pleiotropy), for which the researchers conducted sensitivity tests.

The study design and analyses adhered to the Strengthening the Reporting of Observational Studies in Epidemiology using Mendelian Randomization (STROBE-MR) guidelines and comprised the following:

First, linkage-disequilibrium score regression (LDSC) analyses were used to quantify whether genetic variants associated with subtype-specific coffee intake also correlate with AMD risk. Second, two-sample univariable Mendelian randomization (UVMR) models were used to assess causality using GWAS-derived single-nucleotide polymorphisms (SNPs). Finally, Bayesian colocalization analysis was used to identify shared genetic variants between subtype-specific coffee consumption and AMD risk.

Study findings

Genetic correlation (LDSC) analyses revealed a significant overlap between the genetic predisposition to instant coffee intake and the subsequent risk of dry AMD, suggesting shared DNA signals between the two traits across the human genome. In contrast, other subtypes of coffee consumption showed no such correlation. Furthermore, no association was observed between coffee intake and the risk of wet AMD.

UVMR analyses confirmed these findings and established a causal link. Specifically, each standard deviation increase in instant coffee consumption was associated with a 7.92-fold increased risk of dry AMD (Odds Ratio [OR] = 7.92; 95% Confidence Interval: 1.79 to 35.15; p = 0.006).  After statistical correction for multiple comparisons, the finding remained significant (adjusted p = 0.048). Sensitivity analyses were also conducted to support the robustness of these results.

Colocalization analysis did not detect any shared genetic variants or genome regions between coffee intake and AMD incidence. These findings suggest that processing byproducts, additives, or chemical alterations resulting from dehydration and reconstitution methods unique to instant coffee may contribute to the risk of dry AMD. The paper suggests that instant coffee can contain acrylamide, oxidized lipids, and other compounds not present in fresh brews.

Conclusions

The present study establishes a statistically significant causal genetic association between the consumption of instant coffee and the risk of dry AMD, though the precise magnitude of this risk has a wide margin of uncertainty, as indicated by the broad confidence interval. While the study datasets were derived from a predominantly European cohort, thereby limiting their global generalizability, the causal nature of the observed results prevents their dismissal due to dietary confounds.

Study results suggest that patients with early-stage AMD and individuals with a genetic predisposition to AMD might consider reducing their intake of instant coffee, opting instead for fresh brews. Clinicians and public health policymakers should weigh this evidence when advising patients about the potential drawbacks of highly processed foods like instant coffee.