Higher protein intake in middle age is associated with greater declines in kidney function over time, researchers reported online ahead of print in Nephrology Dialysis Transplantation.
Massimo Cirillo, MD, of the University of Salerno in Salerno, Italy, and colleagues collected data on overnight urinary urea, serum creatinine, estimated glomerular filtration rate (eGFR), and other variables in 1,522 men and women aged 45-64 years. Subjects were participants in the Gubbio study, an ongoing population-based investigation in Gubbio, Italy. The investigators re-assessed serum creatinine, eGFR, and other variables in 1,144 of 1,425 survivors after 12 years of follow-up.
At baseline, the study population had a mean eGFR of 84 mL/min/1.73 m2 as calculated using the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equation and protein intake of 1.34 g/day per kilogram of ideal weight as assessed by measurements of overnight urine excretion of urea nitrogen.
Cross-sectional analyses showed that each 1 g/day increment in protein intake was associated with a 4.7 mL/min/1.73 m2 increment in eGFR. Longitudinal results demonstrated that, after 12 years of follow-up, study subjects had experienced a mean 11.6 mL/min/1.73 m2 decline in eGFR. Each 1 g/day increment in protein intake was associated with a 4.1 mL/min/1.73 m2 decline in eGFR and a 78% increased likelihood of having an eGFR below 60 mL/min/1.73 m2.
“The study reports the first evidence that, in a sample of the middle-age general population, higher protein intake is associated cross-sectionally with higher eGFR and longitudinally with greater eGFR decline over time,” the investigators staged. “Findings were similar for both sexes, independent of several variables, and consistent in subgroup analyses.”
The study’s findings agree with clinical studies demonstrating short-term GFR stimulation by protein intake and unfavorable effects of high protein diet in CKD, Dr. Cirillo’s team said.
The investigators noted that the eGFR decline in their study population averaged rates much slower than observed in the CKD population. “Thus, it is uncertain if the association of protein intake with the slow eGFR decline within the general population is relevant also to the fast eGFR decline in patients with chronic kidney disease,” they wrote.
In addition to the observational design, the authors pointed out, other study limitations included the use of a single overnight urine collection and the lack of information about various types of dietary protein, other nutrients, other age strata, other ethnic groups, and true GFR.