Serum levels of C-Terminal Telopeptide (CTX) are Associated with Muscle Function in Community-Dwelling Older Adults

Abstract

Background
Markers of bone metabolism have been associated with muscle mass and function. Whether serum cross-linked C-terminal telopeptides of type I collagen (CTX) is also associated with these measures in older adults remains unknown.


Methods
In community-dwelling older adults at high risk of falls and fractures, serum CTX (biochemical immunoassays) was used as the exposure, while appendicular lean mass (dual-energy x-ray absorptiometry) and muscle function (grip strength [hydraulic dynamometer], short physical performance battery [SPPB], gait speed, sit-to-stand, balance, Timed Up and Go [TUG]) were used as outcomes. Potential covariates including demographic, lifestyle, and clinical factors were considered in statistical models. Areas under the receiver operating characteristic (ROC) curves were calculated for significant outcomes.


Results
Two hundred and ninety-nine older adults (median age: 79 years, interquartile range: 73, 84; 75.6% women) were included. In multivariable models, CTX was negatively associated with SPPB (β = 0.95, 95% confidence interval [CI]: 0.92, 0.98) and balance (β = 0.92, 0.86, 0.99) scores, and positively associated with sit-to-stand (β = 1.02, 95% CI: 1.00, 1.05) and TUG (β = 1.03, 95% CI: 1.00, 1.05). Trend line for gait speed (β = 0.99, 95% CI: 0.98, 1.01) was in the hypothesized direction but did not reach significance. Area under the ROC curves showed low diagnostic power (<0.7) of CTX in identifying poor muscle function (SPPB: 0.63; sit-to-stand: 0.64; TUG: 0.61).


Conclusions
In older adults, higher CTX levels were associated with poorer lower-limb muscle function (but showed poor diagnostic power for these measures). These clinical data build on the biomedical link between bone and muscle.