• Greater cardiorespiratory fitness was linked to slower decline of cystatin C eGFR over 5 years.
• More research is needed to explore exercise-based interventions for preserving kidney function.

Increasing levels of cardiorespiratory fitness were linked to slower declines in kidney function, according to study data published in Medicine & Science in Sports & Exercise.

Exercise may help to slow kidney function decline for patients before chronic kidney disease onset, according to Shun Yoshikoshi, PhD, specially appointed assistant professor at the Institute of Health and Sport Sciences at University of Tsukuba in Japan, Keisei Kosaki, PhD, assistant professor at the institute, and colleagues. Thus, the researchers aimed to explore the effect of higher cardiorespiratory fitness on kidney function decline among adults in a prospective cohort study.

“We wanted to examine whether higher cardiorespiratory fitness was associated with better preservation of kidney function over time in individuals with preserved kidney health,” Yoshikoshi told Healio.

In a secondary analysis of the Aging Kidney Study, the researchers assessed baseline cardiorespiratory fitness for 198 adults (median age, 61.4 years; 73.7% women) and analyzed their kidney function for up to 5 years.

At baseline, adults completed a submaximal cycle ergometer test, during which oxygen uptake and carbon dioxide output were measured using a gas exchange analyzer to assess cardiorespiratory fitness. Kidney function was assessed annually for up to 5 years using serum creatinine- and cystatin C-based eGFR.

Results showed that cardiorespiratory fitness was significantly associated with cystatin C-based eGFR slope, but not creatinine-based eGFR slope, according to the researchers.

“Creatinine levels are influenced by muscle mass and other nonkidney factors, particularly in studies involving physical fitness,” Yoshikoshi said. “Our findings highlight the importance of considering how kidney function is assessed when investigating the relationship between physical fitness and kidney health.”

In addition, higher levels of cardiorespiratory fitness were linked to a slower decline of cystatin C-based eGFR (beta coefficient = 0.011; 95% CI, 0.002-0.02). Each 1 standard deviation increase in cardiorespiratory fitness was linked to a lower risk for cystatin C-based eGFR decline of at least 20% (HR = 0.64; 95% CI, 0.43-0.94).

Overall, the findings suggest that higher levels of cardiorespiratory fitness were linked to slower rates of age-related kidney function decline over 5 years, according to the researchers.

“Although our findings cannot establish that improving fitness will prevent kidney function decline, they highlight cardiorespiratory fitness as a potentially important and modifiable factor to consider in the context of healthy kidney aging,” Yoshikoshi said.

Future research is needed to explore how exercise interventions may help preserve kidney function over time, Yoshikoshi said.

“Because detecting subtle changes in kidney function using eGFR may be challenging in individuals with preserved kidney function, future studies incorporating more comprehensive assessments of kidney health, including additional kidney-related biomarkers and measures, would be valuable,” he said.

Shun Yoshikoshi, PhD, can be reached at nephrology@healio.com.