Circulating neurodegenerative brain injury markers and hip fracture and fall hospitalizations: the Cardiovascular Health Study

Individuals with dementia have a heightened hip fracture and fall risk but whether markers of brain injury are associated with hip fracture and falls is unknown. We tested the hypothesis that higher circulating brain injury markers were associated with increased risk of hip fracture and fall hospitalizations. Brain injury markers were measured in 2141 participants (mean age 77.9 yr; 60% women). Brain injury markers included neurofilament light chain (NfL), a marker of axonal injury; glial fibrillary acidic protein (GFAP), a marker of astrocytic injury; total Tau, whose many functions include neuron microtubule stabilization; and ubiquitin carboxy-terminal hydrolase L1 (UCH-L1), a major protein of neurons. Incident hip fractures and hospitalizations for falls were identified through participant report and confirmed with medical records or medicare claims. Hazard ratios were computed for a doubling exposure (log2 transformed brain injury marker) using multivariable-adjusted Cox models. After a median follow-up of 11 yr, 304 incident hip fractures and 284 incident fall hospitalizations occurred. Doubling of GFAP and NfL were associated with a 22% (p = .048) and 42% (p < .001) higher risk of hip fracture, respectively. Additional adjustment for cognitive function, gait speed, grip strength, inflammatory markers, and depressive symptoms had no effect on results. Models that adjusted for all 4 brain markers showed that only NfL was independent of the other markers. Neurofilament light chain was also associated with a 47% increase risk of hospitalization for falls. There was no association of total Tau or UCH-L1 with hip fracture or falls. GFAP was also unrelated to fall hospitalizations. Neurofilament light chain was independently associated with an incident risk of hip fracture and fall hospitalizations. These results suggest that subclinical degrees of brain injury may contribute to falls and hip fracture. Future research is needed to test whether the association between NfL and hip fracture is independent of falls.