Acid-base balance affects muscle quality in older adults leading to less muscle mass and strength. Individuals with knee osteoarthritis (OA) have less muscle mass and strength. It is unknown if OA’s effect on function and strength is mediated by acid-base balance.
Purpose: This study examined associations between dietary acid production, physical function, muscle strength, and body composition in older obese adults with knee osteoarthritis. Higher acid load is hypothesized to be associated with lower physical function, strength and lean body mass (LBM).
Methods: Baseline data from the Intensive Diet and Exercise for Arthritis (IDEA) trial were used for this analysis. Measurements from IDEA included a 3-day food record to calculate daily potential renal acid load (PRAL)PRAL, 6-min walk distance, LBM via dual energy x-ray absorptiometry, and concentric knee extensor and flexor strength. Estimated potential renal acid load (PRAL in mEq H+ ions) = (0.49*mg protein) + (.037*mg phosphorus) - (.021*mg potassium) - (.026*mg magnesium) - (.013*mg calcium). Associations were determined by Pearson correlations.
Results: Data obtained from 388 participants (age=65.8±6.1 yrs; 70.4% female; body mass index=33.7±3.8 kg/m²) were used in the analysis. Mean values were: PRAL score (8.9±13.8 mEq/d); LBM (56.0±12.0 kg); 6-min walk distance (476.5±82.6 m); concentric knee extensor (60.2±26.0 Nm) and knee flexor (30.2±14.7 Nm) strength. PRAL showed significant positive associations with concentric knee extensor strength (r=.19; p=.011), knee flexor strength (r=.19; p=.012), and LBM (r=.22, p<.001).
Conclusion: The physiological importance of the statistical relationship observed for high PRAL (higher acid load) and high physical function and knee extensor and flexor strength, although minimal (r~.2), opposes our hypothesis. These discrepant findings may be from using an indirect measure acid production, presence of OA in this cohort, and the accuracy of self-reported dietary records.