Is exercise protective against hearing loss?

Higher muscular and performance fitness* is inversely associated with the incidence of hearing loss, with a clear dose-response particularly with vertical jump height and single-leg balance, the Niigata Wellness Study has shown.

Studies have shown that exercise regulates inflammation and oxidative stress, which have both been linked to hearing loss. [Oxid Med Cell Longev 2016;2016:7239639; Front Aging Neurosci 2015;7:86] “[The findings in these studies] suggest that low physical fitness may be a risk factor for hearing loss,” said the researchers. “Hearing loss is associated with higher risks of depression, dementia, and mortality; thus, identifying preventable risk factors for hearing loss is an important challenge for public health.”

This prospective analysis comprised 21,907 Japanese individuals (median age 49 years, 64 percent male) without hearing loss who underwent annual physical fitness evaluations from April 2001 to March 2002. Hearing loss was defined as >30 dB at 1 kHz or >40 dB at 4 kHz or both. [Am J Med 2021;134:235-242.e4]

During a median follow-up of 5.8 years, about 13 percent (n=2,765) of participants developed hearing loss (unilateral and bilateral).

A significant inverse association was observed between muscular and performance fitness and development of unilateral and bilateral hearing loss (p_trend<0.001). Adjusted hazard ratios (HRs) across muscular and performance fitness index quartiles (Q)1, 2, 3, and 4 were 1.00 (reference), 0.88, 0.83, and 0.79, respectively (p_trend<0.001).

Other analyses

Stratifying by physical fitness variable, after adjusting for potential risk factors**, unilateral and bilateral hearing loss was inversely associated with vertical jump height (HR ranging from 0.70 to 0.79 [Q2–Q4]; p_trend<0.001) and single-leg balance (HR ranging from 0.79 to 0.92 [Q2–Q4] p_trend<0.001). “[These suggest that] vertical jump height and single-leg balance, which can be easily and objectively assessed in healthcare settings, [may] serve as predictors of the risk of developing hearing loss,” the researchers explained.

Stratifying by age, a significant inverse association was found between incident unilateral and bilateral hearing loss and whole-body reaction time among older (p_trend=0.003) but not younger individuals (p_trend=0.337).

Results from an alternative analysis (wherein low- [1 kHz] and high- [4 kHz] frequency hearing loss was evaluated separately) mirrored the main findings (p_trend<0.001 [1 kHz] and p_trend=0.002 [4 kHz]). In this analysis, 4 percent (n=931) of participants developed unilateral and bilateral low-frequency hearing loss, while 10 percent (n=2,179) developed unilateral and bilateral high-frequency hearing loss during follow-up.

Possible mechanisms involved

Preclinical data show that chronic inflammation may damage the auditory system. [Ageing Res Rev 2017;40:142-148; J Neurosci 2016;36:11308-11319] The increased antioxidant capacity and reduced oxidative stress (which induces apoptosis of cochlear cells) with exercise may have a positive effect on inflammatory markers. [Sports Med 2017;47:277-293; Eur Arch Otorhinolaryngol 2017;274:1821-1834; Front Aging Neurosci 2019;11:98]

Another possible mechanism that could elucidate the role of exercise in hearing preservation is blood flow, noted the researchers. “Reduced cochlear blood flow causes cell damage and has been suggested to be partially involved in decreasing hearing sensitivity. Exercise training has favourable effects on vascular structure and function and improves endothelial function.” In a meta-analysis, exercise-trained athletes had superior microvascular dilator function than healthy controls. [Med Sci Sports Exerc 2015;47:1485-1494]

However, despite the large sample, long follow-up, and use of several physical fitness parameters, the findings were not adjusted for noise exposure or family history of hearing loss. Sample bias may have also been introduced given the nonrandomized study design, the researchers noted.

Also, not all participants were tested at baseline for all five fitness parameters. “Nevertheless, we observed similar results in a sensitivity analysis after multiple imputations of missing exposure and covariate data,” they said. Taken together, the findings underline the potential of physical fitness to delay or prevent the development of hearing loss.