Physical Activity and Hearing Health
Several population-based epidemiological studies have demonstrated a relationship between physical activity and odds of hearing loss. However, these data to date have been limited to cross-sectional analyses, where cause and effect cannot be discerned. In a first study of physical activity on hearing loss in animals, Han et al. (2016) examined the impact of increased physical activity in mice (CBA/CaJ) on age-related hearing loss (ARHL). In the study, mice were divided into groups based on age and physical activity. Physical activity was modulated by the presence of a running wheel; mice were single-housed in a cage with or without a running wheel. The mouse’s choice to use the running wheel was voluntary, but the number of revolutions of the running wheel was monitored through a computer module.
Mice started wheel running (WR) at three months (m), age-matched animals without a running wheel served as controls. The mice were then monitored until 24 m of age. WR activity peaked at approximately 6 m (12000 meters/day) of age in the group and gradually decreased to an average of 4000 meters/day by the age of 24 m. The mice in the WR group demonstrated significantly lower weight at 6 m and 12 m compared to controls, and this difference was no longer observed at 24 m.
In regards to hearing (as measured by ABR), WR mice on average had better hearing at 24 m compared to non-WR mice of the same age. However, the reduction in age-related hearing loss was limited to low and mid frequencies of the mouse auditory system (< 16 kHz). These findings were supported by histological analysis of hair cell and neural integrity. However, histological data also supported decreased the loss of hair cell and spiral ganglion neurons in more basal regions (> 16 kHz). This long-term WR also resulted in significant decrease in some 15 genes involved in inflammation.
Overall, the results suggest that physical activity can alter the progressions of ARHL and support findings of human population-based studies. The limitation of the effect to more apical regions of the cochlea may be due to influence on vascular integrity or genetic factors contributing to hearing loss in this strain of mice. Also, the WR was voluntary, and it was suggested that if animals were forced to run more there may be extended protection to more basal regions of the cochlea.
Han et al. (2016) Effects of Long-term Exercise on Age-Related Hearing Loss in Mice, The Journal of Neuroscience 36(44):11308-11319.