Characteristics of included studies and results of bias assessment

In general, most of our selected papers had low bias and were of high quality. As shown in Additional file 3, the risk of bias was rated as “low” for 25 of the 29 papers, “high” for 2 papers, and “uncertain” for 2 papers. Twenty of the 26 papers were from the United States, one involved both Kuwait and Saudi Arabia, one was from both South Africa and China, and the other seven from Canada, South Africa, Germany, Turkey, Nigeria, Australia, and Swaziland. The sample size varied from 7 to 19,223 people, with 24 studies having fewer than 1,000 and 4 papers having more than 10,000. There were 22 quantitative studies and 7 qualitative studies. Four of the studies involved teenagers, while the others were conducted on adults. Four of the studies included just female hearing-impaired participants, while none involved only male hearing-impaired participants. Twenty-two studies were conducted by survey, three by interview, and four by focus groups (Table 2).

Table 2 Characteristics of study includedTools for measuring health literacy

The most used assessment tools in the articles we searched were the Rapid Estimate of Adult Literacy in Medicine (REALM), Test of Functional Health Literacy in Adults (TOFHLA), Newest Vital Sign (NVS), Health Literacy Skills Instrument (HLSI), European Health Literacy Survey (HLS-EU-Q47), and Brief Health Literacy Screen (BHLS). Some studies also used their own developed questionnaires. Table 3 shows some of the sources of health literacy measurement tools. All the tools used for measuring the health literacy of people with hearing impairment classify the level of health literacy into two to four degrees, and all have been tested for validity.

Table 3 Tools for measuring health literacy

As follows, we have summarized the findings of each article according to those listed in Table 4. Although each article does not show the same content due to differences in the purpose of the study, we can still summarize based on what is available.

Table 4 Current status of health literacy among people with hearing impairment and improvement methodsHealth literacy levels of people with hearing impairment

The prevalence of inadequate health literacy among people with hearing impairment is high. Mckee et al. [27] conducted a study with 166 participants with hearing loss and 239 hearing participants without, and showed that 48% of participants with hearing loss have inadequate health literacy and were 6.9 times more likely than hearing people to have poor health literacy. Pollard et al. [19] investigated health-related vocabulary knowledge in a sample of adults through a modified REALM and found that 32% of people with hearing loss received scores comparable to low health literacy scores; all of their study participants were people with hearing disabilities and 80.8% obtained a college degree, implying that even people with hearing disabilities with high or average levels of education may be at risk of lower health literacy. Tolisano et al. [38] found ratings of participants’ hearing were categorized into four grades, and patients with poorer hearing grades C and D had lower health literacy scores measured with the BHLS than those with grades A and B (BHLS score in the range of 11.6–13.6). Wells et al. [39] divided 19,223 older adults into five groups based on their self-reported hearing disability level, including those with severe unaided hearing loss, severe with hearing aid use, mild with assistance, mild without assistance, and no hearing loss. Of these, the unaided mild, aided severe and unaided severe hearing loss groups showed lower health literacy than the other groups, although this connection diminished with the use of hearing aids.

The barriers to health literacy for people with hearing impairment

Among the people with hearing impairment, there is a lack of knowledge and misconceptions about diseases, such as cervical cancer [18, 23], ovarian cancer [25], breast cancer [24], HIV/AIDS [17], COVID-19 [41], and diabetes [35]. People with hearing impairment also had limited access to health information and encounter difficulties in seeking health information [49]. Several studies were conducted on a hearing-impaired group and a control group to compare their knowledge on cervical, ovarian, and breast cancers after listening to a graphic-rich video in American Sign Language with English subtitles regarding cancer [18, 23, 25]. The studies obtained similar results; women in the control group performed better before watching the video, while following the intervention, both groups’ knowledge on relevant tumors improved significantly [18, 23,24,25]. These findings imply that the health literacy of people with hearing impairment can be improved if there are more effective ways to expose them to health information and provide more access to it.

People with hearing impairment tend to visit their doctors more often than those with good hearing, but they can have more difficulty communicating with professionals [50], which is consistent with the findings of a survey of American Sign Language (ASL) interpreters [51]. In Stevens et al.’s study [36], more than 90% of people with hearing impairment reported problems with poorly communicated information and communication difficulties when their name was called with the presenter’s back being turned, as well as communication over the telephone, which can affect the quality of patient care, satisfaction, and health outcomes. According to Steinberg et al. [15], adults with hearing impairment who used ASL were distrustful, fearful, and frustrated with medical care and believed that if doctors could communicate with them in sign language or with a live interpreter, it would help them establish good communication with the doctor and improve their satisfaction with the medical service. Similar communication challenges were observed among teenagers with hearing disabilities [37], with 55.7% preferring written prescriptions or care procedures and 87.5% preferring sign language communication. A study [28] has shown that when pharmacists lack patience or understanding of the real needs of people with hearing impairment when they seek medication care, the bond between them can be weakened and, in turn, can affect the safe administration of medication to patients. All of these findings illustrate the importance of effective communication between patients and doctors about medication, treatment, and health outcomes.

The impact of health literacy levels on health management among people with hearing impairment

People with both hearing impairment and limited health literacy were more likely to have higher medical costs [39]. In addition, people with hearing loss have very limited awareness of health insurance and have little access to the related information [40]. Willink et al. [40] discovered that Medicare participants who had a little or a lot of hearing impairment were 18% and 25%, respectively, more likely to report having difficulty understanding Medicare than those who did not have hearing problems. Approximately 20% of Medicare enrollees with hearing loss reported that their hearing disability made it hard to find information about Medicare. This also implies that methods to assist people with hearing loss in understanding Medicare should be consistently developed.

Methods for improving health literacy

Online education can help enhance the health knowledge of people with hearing impairment as well as their capacity to seek health information on the internet [14, 18, 23, 25, 33]. Palmer et al. [33] reported that the bilingual modality via both the signer and closed captioning provided better access to cancer genetics information for less-educated ASL users compared to the monolingual modality. This study supports that materials prepared with sign language and extra captioning and graphics improve the sign language user’s understanding and satisfaction. Short Message Service (SMS) can help people with hearing loss become more aware of hypertension and healthy living. However, because of the special demands and preferences of sign language users, SMS services must be investigated further to fulfill the needs of the hearing impaired. Haricharan et al. [32] suggested numerous strategies to improve SMS campaigns for people with hearing disabilities, including the use of images, combination of SMS with signed drama, use of 'signed’ SMS, and linkage of SMS campaigns to interactive communication services.

Additionally, communication issues between people with hearing impairment and health care providers need to be addressed. Most people that are hard-of-hearing in the survey mentioned difficulties in communicating with doctors, the obscurity of some terminology, and even misunderstandings [36]. They hoped to communicate with the doctor in sign language or have a sign language interpreter on-site to help them speak with their doctor, which would increase their satisfaction with health services, strengthen the doctor-patient relationship, and improve their health outcomes [15, 36, 37]. To facilitate communication between patients with hearing impairments and healthcare professionals, it is essential to pre-educate healthcare professionals about people with hearing loss [20]. In Hoang et al.’s study, medical students were divided into two groups based on whether they had undertaken a community education program on hearing impairment. When knowledge of the overall “deaf culture “ in the healthcare setting was assessed, the summary scores varied widely—26.9 for those who had completed the education program, 17.1 for the medical school faculty, and 13.8 for those who had not completed the education program [20]. Overall, the faculty members scored similarly to medical students who did not complete the educational program on issues particularly relevant to interactions with hearing loss patients. This research proved that primary education is crucial in interacting with deaf patients, regardless of clinical expertise [20].