How Does Coffee, Tea Consumption Impact Estimated GFR?
Consuming multiple cups of coffee a day is likely to be safe for the kidneys in the general population, and is associated with an increase in estimated glomerular filtration rate (eGFR), according to findings of a study from the Netherlands.
The researchers analyzed data from the ‘Doetinchem Cohort Study', a lifestyle and biological risk factors study of inhabitants of the Dutch town Doetinchem. From 1987–1991, 12,405 people completed a health questionnaire and had a physical examination (ages 20–59). Of those, two-thirds of a random sample (n=7,768) were re-invited to be examined in 1993–1997 (round 2; n=6,113), 1998–2002 (round 3; n=4,916), 2003–2007 (round 4; n=4,520), and 2008–2012 (round 5; n=4,017).
Participants' eGFR was assessed by using the Chronic Kidney Disease Epidemiology Collaboration equation based on plasma creatinine and cystatin C.
Results of the age and sex-adjusted analysis showed that coffee consumption was associated with a higher eGFR, with ßs of 1.29, 1.19, and 1.28mL/min/1.73 m2 for participants drinking 3–4, 5–6, or >6 cups a day, respectively, compared with <1 cup a day (P=0.04).
The eGFR levels increased when values were adjusted for magnesium, potassium, and caffeine, demonstrating significant ßs of 1.35, 1.36, and 1.61mL/min/1.73 m2 for those consuming 3–4, 5–6, or >6 cups a day, respectively, compared with <1 cup a day (P=0.01).
The authors assert that their findings display a "clear dose-response relation, with a higher eGFR with increasing intake of coffee." They also note that this relationship is not accounted for by a range of biological risk factors and coffee components, including caffeine. However, given that blood samples in the study were nonfasting, it is not possible to rule out acute effects of caffeine entirely.
Low eGFRs are risk factors signals of early kidney failure, and with the findings from this study, it's possible to speculate that coffee consumption may protect against a decline in kidney function. However, the increase in eGFR is small, and the authors note further research is needed. Specifically, research into coffee compounds, such as quinides and niacin, are needed to possibly explain the slightly higher eGFR seen in coffee drinkers.
They concluded that, “although current findings suggest that coffee consumption seems to influence eGFR, the slightly increased eGFR does not necessarily reflect improved kidney function. The participants in this study had normal eGFR at baseline, and an increase in eGFR may reflect glomerular hyperfiltration.”
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