Markers of bone turnover after 12 months of exercise in patients with chronic kidney disease 3-5: a sub-study of RENEXC – a randomized controlled trial

Background Bone and mineral disorders are common in patients with chronic kidney disease (CKD), leading to poor quality of life, high fracture risk, and increased morbidity and cardiovascular mortality. Parathyroid hormone (PTH) and bone-specific alkaline phosphatase (bALP) are frequently used to assess bone turnover, but markers such as procollagen type I N-terminal propeptide (intact PINP) and tartrate-resistant acid phosphatase isoform 5b (TRAP5b), which reflect bone formation and resorption, may provide more specific insights into bone remodeling. This study aims to investigate the effects of balance and strength exercises on bone turnover markers in patients with CKD not undergoing kidney replacement therapy. Methods This study is a sub-analysis of the RENEXC trial, a randomized controlled exercise intervention lasting 12 months. A total of 151 CKD stage 3–5 patients were randomly assigned to either strength or balance exercise, both combined with endurance exercise. Exercise intensity was monitored using the Borg Rating of Perceived Exertion (RPE) scale. Bone turnover markers, including intact PINP and TRAP5b, were measured at baseline and after 12 months. Results After 12 months of exercise both groups significantly improved physical performance, no significant changes were observed in intact PINP or TRAP5b across the entire cohort. However, subgroup analysis revealed that women in the balance group experienced a significant reduction in TRAP5b, indicating a potential decrease in bone resorption. Additionally, both exercise groups showed an increase in the proportion of patients with TRAP5b values indicative of low bone turnover, suggesting a protective effect on bone resorption. Higher phosphate and PTH levels were associated with positive Δ intact PINP as well as positive Δ TRAP5b, while higher 25(OH)D levels were associated with negative Δ TRAP5b values. Conclusions While no significant changes in bone turnover markers were observed in the overall cohort, the results suggest that balance exercise may reduce bone resorption in women with CKD. Additionally, both strength and balance exercises appeared to diminish bone resorption as indicated by TRAP5b levels. These findings warrant further investigation into the long-term effects of exercise on bone health in CKD, with a particular focus on the mechanisms underlying these responses. Trial registration NCT02041156 at www.ClinicalTrials.gov. Date of registration January 20, 2014. Retrospectively registered.