The Missing Link Between Coffee Consumption and AKI–Water

To the Editor:

Using data from the Atherosclerosis Risk in Communities Study, Tommerdahl et al.,¹ recently published in KI Reports findings supporting an inverse association between self-reported daily coffee consumption and incident acute kidney injury (AKI). The authors enrolled a large sample consisting of 14,207 middle-aged and older adults (45–64 years) and adjusted for several covariate factors that may influence the results (e.g., age, sex, race, smoking status, physical activity level, alcohol consumption, etc.). Following adjustments, the authors showed a dose-dependent risk reduction for AKI, in that those who consumed 2 to 3 cups per day of coffee showed the lowest risk of AKI during a hospital stay and drinking any amount of coffee was associated with an 11% reduction of developing AKI. The mechanistic underpinnings of these results were attributed to the potential benefits of caffeine or bioactive compounds in coffee on renal function. However, no discussion was provided on the relationship between fluid balance and renal health, despite a key nutrient of coffee beverages being water. Given that hospitalized patients presenting with fluid deficits or dehydration exhibit a 4-fold greater likelihood of developing AKI, compared to well hydrated patients,² we believe further consideration of the influence daily fluid intake on AKI is warranted in interpretating the results by Tommerdahl et al.¹

For instance, in the USA, greater than 95% of adults aged from 51 to 70 years have poor drinking habits coupled with a greater than 4-fold likelihood of developing a chronic disease within 3 to 6 years.³ Mechanistically, chronic low fluid intake or hypohydration stimulates an increase in arginine vasopressin, which is associated with elevated risk of chronic kidney disease.⁴ Stated otherwise, chronically elevated arginine vasopressin may signal a hemodynamic frailty phenotype, resulting in reduced renal resiliency and increased plasma hypertonicity and opportunity for injury.⁵ Taken together, it is biologically plausible that because daily fluid intake was not adjusted for, and the inherent limitations of varying caffeine content of coffee beverages, the benefits of self-reported daily coffee consumption on AKI development in hospitalized adults may be indicative of adequate fluid consumption behaviors and thus reduced vasopressin renal burden and AKI development.