Study Suggests Instant Coffee May Have Negative Consequences For Long-Term Eye Health – CoffeeTalk

A new genetic study has found that just one extra cup of instant coffee a day could significantly increase the risk of developing dry AMD, shedding fresh light on how our daily beverage choices may shape long-term eye health. The study published in the journal Food Science & Nutrition 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).

The study found that there was 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 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.

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 can slow AMD progression, the condition is irreversible, underscoring the need for prevention-focused research and policy. 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).

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

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. The causal nature of the observed results prevents their dismissal due to dietary confounds.

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