Vestibular roll tilt thresholds partially mediate age-related effects on balance.

Background: It has been well-established that both vestibular function and balance degrade with age and that balance degradation contributes to falls. While multiple causes contribute to balance declines, there have been few empirical investigations of the specific sensory contributors to balance that mediate (i.e., explain a significant fraction of) the effect of age on balance. Objective: To determine if vestibular function significantly mediates the effect of age on balance, and to quantify the fraction of any such statistically significant age-effect on balance using previously published vestibular threshold and balance data. Methods: Balance was quantified as complete/incomplete on a standard Romberg 4-condition foam balance test. Vestibular thresholds were determined using standard methods with motion provided by a Moog 6DOF motion platform. Standard mediation analyses were performed to determine if any of the five vestibular thresholds measured (0.2Hz roll tilt and 1 Hz roll tilt, yaw rotation, y-translation, and z-translation) significantly mediated the previously reported age-effect on balance. Results: 0.2Hz roll tilt thresholds were found to significantly mediate the relationship between age and balance, whether we considered all subjects or just the subjects above the age of 40 (above which vestibular thresholds increase with age). Depending on the exact age cut-off implemented between 37 and 42 years of age, 0.2 Hz roll tilt thresholds explained (mediated) between 33% and 55% of the total age-effect on balance. Conclusion: Vestibular function may mediate approximately 50% of the widely-reported age-effect on balance. If confirmed by future studies, this may provide an opportunity to improve balance (and presumably reduce fall risk) via specific therapies tailored to improve vestibular function.