This is the first pilot study to define explicit risk associations between hearing loss and psychiatric disorders utilizing a large national population. Based on subgroup analysis, we also identified the most common psychiatric disorders caused by hearing loss, with the highest to lowest rates ranked as post-traumatic stress syndrome (PTSD), depression, and anxiety disorders. In this study, we provide more detailed information on the risk of psychiatric disorders in patients with hearing loss. For health care professionals, better health care plans can be developed, and for public health workers, more comprehensive social welfare programs can be established to reduce overall health care costs.

In Table 2, we list the risk factors for psychiatric disorders and calculate the hazard ratio. Compared to other comorbidities and demographic variables, hearing loss had the highest risk of developing psychiatric disorders. In Table 3, we compare the effects of different conditions on the hearing loss group. The risk of psychiatric disorders in the hearing loss group was found to increase with age. The elderly group’s hazard ratio was greater than that of the younger group (2.610 and 2.555). This could be related to other comorbidities. Systemic diseases are already a stressor for psychiatric disorders [12], and hearing loss is also considered a stressor [4], so a higher risk can be expected when both disorders are present, and this hypothesis is confirmed by our statistical data. In addition, the effect of seasonal changes on patients with hearing loss can be explained by seasonal affective disorder. Psychiatric disorders are more likely to develop in the winter [13], and this is no exception in the hearing loss community. In Additional file 2: Table S3, an additional test was conducted due to concerns about possible discrepancies in the diagnosis of hearing loss between doctors in different specialties, but the results did not appear to be significantly different.

In compiling the data, we found a phenomenon: the more urbanized the patient was, the higher the risk of developing psychiatric disorders. Another study supports our findings [14]. We believe this is because urban living requires more effective communication. This means that patients with hearing loss need to be fully attentive to every message they receive, which inevitably stresses patients with hearing loss. In Taiwan, most medical centers are in highly urbanized areas, where they receive more patients with hearing loss and more complex diseases. As a result, patients at medical centers have a higher risk of developing psychiatric disorders after follow-up visits (adjusted HR = 2.630). Patients in medical centers usually have more complicated medical problems.

Scholars have confirmed that hearing loss is a risk factor for psychiatric disorders [4] and that it also contributes to cognitive decline [15]. We make inferences about this observation, which can be divided into two main categories: psychological and physical. Psychologically, hearing loss is stressful for patients who need to compensate for their hearing deficits by reading lips. Furthermore, since the COVID-19 outbreak, the public has been wearing masks, which makes it more difficult for patients with hearing loss to understand the verbal communication of others [16]. Despite the fact that hearing aids have been shown to be effective in lowering the incidence of psychiatric disorders, there is still a gap when compared to the general population, most likely due to the noticeable appearance of hearing aids and poor sound recognition [17]. Additionally, when patients with hearing loss suffer from psychiatric disorders, they are unable to communicate effectively with physicians in psychiatric outpatient clinics because most physicians are not proficient in sign language. Therefore, a third person who understands sign language is usually needed to relay the message, but this may distort the message and make it difficult for the physician to have a more accurate handle on the condition. Physiologically, studies have shown that when a patient suffers from hearing loss, there are changes in the volume of relevant areas of the brain, causing the surrounding brain tissue to be affected and eventually causing cognitive impairment [18, 19]. This progression is very slow, and by the time psychiatric symptoms appear, a significant amount of brain tissue has already atrophied.

The Kaplan‒Meier method for long-term follow-up of cumulative risk of psychiatric disorders had a statistically significant log-rank (p < 0.001) (Fig. 2). In our study, patients with hearing loss may have developed symptoms slowly over time, in addition to psychiatric symptoms in the short term.

Kaplan‒Meier analysis of poor prognosis stratified by hearing loss with the log-rank test. Kaplan‒Meier analysis showed that patients with hearing loss had a significantly higher rate of psychiatric disorders than matched controls (log test p < 0.001)

In our event subgroup analysis, we found that patients had the highest risk of ASD and PTSD within the first five years of diagnosis (adjusted HR = 3.371). We also found other articles that supported our data and hypothesis [20] that acquired hearing loss may result in ASD or PTSD symptoms, as well as underlying stressful pre-existing relationship breakdowns, job failures, or an inability to adapt. In the long term, the risk of anxiety and depression is more than three times greater in these patients. Charlene J. Crump et al. showed that patients with hearing loss were often unable to communicate effectively with their psychiatrists during long-term local follow-up visits, which then affected their judgment and treatment, leading to a worsening of their disease [21]. Age, chronic disease, sensory stimulation loss, e.g., hearing loss, and other variables can all contribute to cognitive decline. The use of cochlear implants [22] or hearing aids [23] can significantly decrease cognitive decline, improving the elderly's capacity for self-care [24] and lowering the cost of long-term care services.

In addition to evaluating the use of hearing aids or cochlear implants, we recommend that clinicians working with patients who are diagnosed with hearing loss briefly assess the patient’s cognitive and mental status at the outpatient follow-up visit. If psychiatric disorders are suspected, early consultation with a neurologist or psychiatrist for evaluation and treatment is indicated. Some hearing losses, such as age-related hearing loss, progress over time [25]. This means that the sooner a psychiatrist is involved, the better the patient's chances of communicating effectively with him or her.

More importantly, in the public health context, this study provides a more accurate risk ratio than other studies, which can be used to predict the number of patients with psychiatric disorders in the future, as well as to assess the budget for subsidies, such as reducing the cost of hearing aids, cochlear implants, auditory brainstem implants, or sign language education. The strength of this study is mainly in the large sample size obtained from our national database to statistically determine the relative risk, as no previous large-scale study has statistically determined the risk ratio of hearing loss for each psychiatric disorder. In addition, the long-term follow-up made it possible to analyze short-, medium-, and long-term effects at the same time.

However, there are still limitations to this study. First, there is no detailed information on the severity of hearing loss. There is no way to specify the progress of each patient with psychiatric disorders. In other words, we cannot know whether hearing loss is a key incident in the development of psychiatric disorders. It may be that a patient has symptoms of a psychiatric disorder prior to hearing loss but has not been diagnosed. However, this can be minimized by extending the follow-up years to exclude the first year or the first 5 years. Statistically significant differences were seen for most of the subgroups (p value < 0.001). Second, these tables do not include medications other than those used for hearing loss. For example, proton pump inhibitors can lead to depression in some patients with specific physical conditions [26], but we believe that this has very little impact on the results of the study because the percentage of people is small and the condition can be cured by changing the medication. Third, we were unable to perform an accurate sensitivity test to diagnose hearing loss. However, we conducted an additional test, shown in Additional file 2: Table S3, to compare patients with hearing loss diagnosed by otolaryngologists and other specialists who had a poor prognosis when followed up over time. The results were similar. Fourth, patients with each type of psychiatric disorder may have different backgrounds. Therefore, the impact of hearing loss on the development of each psychiatric disorder may be different. The potential mechanisms underlying individual responses remain to be further examined on a large scale.