With the population aging, an increasing number of people are living with hearing impairment, especially during their later-life years. It is said that more than 90% of hearing impairments in the world are age-related  and most of them are irreversible . On the other hand, hearing impairment often has a slow onset and progressive deterioration , which results in detection difficulty unless checked by accurate pure tone measurement. In addition, a large proportion of people regard hearing impairment as a natural process of aging which can be ignorable, so hearing impairment has not yet received enough attention as it deserves . All these factors result in hearing impairment an unrecognized and under-treated health problem .
What we have found among hearing-impaired adults in China is generally consistent with previous studies about the effects of hearing impairment on people’s physical and mental health. People with more severe hearing impairment tend to be older , female , and less educated . Hearing impairment has been proved to correlate with more chronic diseases . And with the deterioration of hearing impairment, people are more likely to have poorer body functions measured by activities of daily living (ADLs) and instrumental activities of daily living (IADLs) [4, 5]. In addition, hearing impairment can also lead to depressive symptoms, such as sadness, hopelessness, helplessness , and exacerbating the decline in individuals' psychosocial well-being .
Our results further demonstrated the association of different severity of hearing impairment with their physical and mental health. The prevalence of impaired ADLs shows an elevated increase for those with severe to profound hearing impairment, compared with moderate hearing impairment. For those with profound hearing impairment, the prevalence of impaired IADLs and depressive symptoms are much higher than those with moderate hearing impairment. The underlying mechanism may be that, ADLs measures basic functions in daily activities and IADLs measures functions in more subtle activities, so hearing impairment may be more related to the decline in certain brain structures that control these functions . And hearing impairment inevitably brings about communication barriers, thus the more probability of falling into depression is conceivable . However, the prevalence of chronic diseases does not show significant differences within groups of severe to profound hearing impairment, which may due to the limited sample size or the selection of reference group.
Since hearing impairment can be difficult to detect and cure, and is closely related to health, it is imperative to raise awareness and take effective measures. For newborns, the screening and prevention of hearing impairment should be taken as early as possible. For those with hearing impairment, especially with moderate and above hearing impairment, it is necessary to provide rehabilitative devices to compensate for the loss of functions, such as wearing hearing aids . It has been proved that people who use hearing aids reported better self-care, lower levels of depression, and better overall health . However, due to the high price of hearing aids, the accessibility and utilization rate are relatively low worldwide . Our findings highlight the need to improve the health of the hearing-impaired population through early detection and making auditory rehabilitation devices such as hearing aids more accessible and affordable.
The limitations of our study are that, first, some hearing and health variables are determined by participants' self-reported data, which may bring some bias. Second, although some confounders have been controlled, other undetectable confounders may also affect the results. The strengths lie in that, first of all, our study focuses on the association between hearing impairment and health outcomes in China, which is a relatively unexplored and prospective topic in developing countries. Second, we apply multiple physical and mental health outcomes to demonstrate the harm of hearing impairment from different perspectives. Third, we not only use three years of CHARLS data to elucidate the complex interplay between hearing impairment and health, but take a step further to investigate different severity of hearing impairment. Finally, we combine both self-reported hearing status and objective measures of hearing using pure-tone tests, which can act as more profound and compelling evidence.