Hearing is one of the basic means of perception and communication which is closely related with quality of life and public health . Despite the importance of hearing in everyday life, hearing impairment is often unrecognized and undertreated, thus resulting in a growing number of people suffering from hearing impairment. Moreover, the hearing impairment risk increases rapidly with age, and the prevalence rate of older adults is significantly higher than other groups . The World Health Organization pointed out that in 2012, about one-third of the world's older adults aged 65 and above had moderate or above hearing impairment . As the global aging intensifies, hearing impairment is becoming an even more serious public health problem . The 2015 Global Burden of Disease Study further found that hearing impairment had become the second chronic disease threatening human health .
In this study, we observed that 54.46% of the total participants reported having fair or poor hearing, which occupied a large proportion of the participants. Besides, hearing impairment in community-dwelling Chinese older adults was found to be independently associated with higher risk of hospitalization. In the age group of 60 and above, compared with participants with excellent or very good hearing, those with good, fair and poor hearing had a shorter time to incident (first) hospitalization (HR = 1.41, 1.58, 1.69, respectively), a greater annual number of hospitalizations (IRR = 1.38, 1.61, 1.68, respectively) and a longer mean last-time duration of hospitalization (factor change = 0.12, 0.16, 0.19, respectively). We did not find a significant association between hearing status and risk of hospitalization among middle-aged Chinese adults, probably due to their relatively better health status. These findings suggest that gradient hearing impairment, which is highly prevalent but undertreated, is a significant risk factor for hospitalization in older adults.
What we have found are in some way consistent with previous studies that hearing impairment is associated with greater utilization of healthcare resources. Hearing impaired older adults used significantly more health services than people with normal hearing [27–30]. Previous researches have also further demonstrated the relationship between hearing status and hospitalization [13, 14]. A study examining civilian, noninstitutionalized US population aged over 70 years old found that hearing loss was associated with higher odds of any hospitalization and higher odds of more hospitalizations for the increase in hearing thresholds, after adjusting for demographic characteristics and cardiovascular comorbidities . For those aged 70–79 years old, the same result was derived that hearing-impaired older adults experienced a greater incidence and annual number of hospitalizations than those with normal hearing . This may imply that encouraging and promoting the access to hearing rehabilitation services would be effective measures in reducing the risk of hospitalization and burden of diseases.
We speculate that some possible mechanisms may account for the associations between hearing status gradients and risk of hospitalization. Common risk factors or pathological processes such as inflammation  or microvascular disease [32, 33] are likely to lead to poor hearing and risk of hospitalization. And social isolation may play an intermediary role in the relationship between hearing status gradients and hospitalization risk, as it can be a potential sequela of hearing impairment, reducing people’s efficacy and perceived self-worth, aggravating depression and does harm to physical and mental health [34–37]. Hearing impairment may also lead to poorer oral literacy, so patients are not able to effectively communicate with physicians and care provider [38–41]. It has been proved that oral literacy is an independent risk factor for hospitalization and a key determinant of health in older adults [42, 43]. Hearing impairment has also been found to be strongly associated with poor cognition, interfering knowledge acquisition and understanding, which may further add to hospitalization risk [44–46]. Besides, those with worse hearing status showed lower rate of wearing hearing aids. But due to lack of more detailed information on the time and frequency of hearing aid use or other auxiliary equipment, we were unable to draw more specific conclusion about the effects of hearing aids.
In this study, due to the limitations of survey data, we lacked information about standardized audiometric assessments in individual level and had to apply self-rated hearing status in this study. Although prior studies have noted that a single-item question about an individual's hearing ability is moderately useful and valid to assess hearing loss and can be used for a population-based study, we have to admit self-rated hearing should not be considered an adequate substitute and its validity has not been evaluated among Chinese middle-aged and older adults [47–49]. The strengths are that we employed the method of prospective cohort study to determine that hearing status gradients could be associated with risk of hospitalization. And hospitalization details were supported by hospital records and other documents objectively, ensuring fidelity of hospitalization information. Moreover, we have taken potential broader implications of these observed associations into account and tried to figure the mechanism for the associations between hearing status gradients and risk of hospitalization.