Background
Dementia is a major global public health concern. It affected approximately 50 million people worldwide [
1]. Dementia prevalence is expected to rise in the near future, especially in China, where its prevalence in a population of 1.7 billion adults aged 60 or older [
2] was 4.6% (8 million) in 2010 [
3], which is expected to increase to 6.7% (23 million people) by 2030 [
4]. Cognitive impairment, characterized by the presence of weakening of one or more cognitive domains like immediate and delayed memory, may develop into dementia [
5]. The prevalence of mild cognitive impairment among Chinese adults aged ≥60 was 12.7% in 2010 [
6]. Cognitive decline is more prevalent in older individuals [
7], and previous studies have shown that the presence of chronic diseases, sensory loss, disengagement in physical, mental or social activity, and exposure to acute and chronic stress may be related to poorer cognitive performance in later life [
8,
9].
Hearing loss, a prevalent chronic condition in older adults, is a key risk factor of cognitive impairment and dementia [
10‐
12]. Approximately 11% of adults aged ≥60 were diagnosed with disabling hearing impairment in China [
13]. Dementia is a major source of disability around the world, and no disease-modifying treatments so far [
14]. Age-related hearing loss may be associated with an increased risk of dementia in later life, which has garnered increasing attention as a potentially modifiable risk factors for dementia and cognitive decline [
10‐
12]. Evidence from a randomized controlled trial regarding hearing support in dementia (i.e., SENSE-Cog Field Trial) demonstrated that employing a sensory intervention to support hearing, such as providing hearing aids, communication training, and supplementary sensory aids to enhance the home environment or foster social inclusion, benefits people with dementia as well as their partner by improving their quality of life, physical functions, psychosocial health and relationship satisfaction [
15,
16]. Moreover, studies have indicated that hearing aid use confers a mitigating effect on the trajectories of cognitive decline by maintaining cognitive function, such as episodic memory [
17,
18].
Although the mechanisms underlying the association of hearing loss with cognitive decline and dementia remain unclear, several hypotheses exist [
19]. One possible mechanism is the shared pathologic etiology. The common factor theory suggested that the association of sensory and cognitive performance is explained by a third common factor, such as an aging brain [
20,
21] or frailty syndrome [
22]. The second hypothesis is biologically plausible given the effects of hearing loss on cognitive load and cognitive reserve, which may be mediated by social isolation or loneliness [
12,
23]. One possible explanation for the association between social isolation, loneliness, and cognitive function is that loneliness or social isolation is associated with unhealthy behaviors or a plethora of chronic diseases related to poor cognition [
24]. The third hypothesis is the information-degradation hypothesis, which posits that increased cognitive load from the compensation of auditory deficits may limit the resources available in performing other cognitive tasks [
25].
One potential way in modifying the association of hearing loss with cognitive decline and dementia may be through increased participation in activities. Previous studies indicated that older adults with hearing loss were more likely to have smaller social networks [
26]. Since the relationship between hearing loss and cognitive impairment may be mediated by social isolation or loneliness [
24], efforts to improve the social networks of hearing-impaired older adults may be beneficial in preventing cognitive decline. Participation in leisurely activities, i.e. gardening, reading or engaging in hobbies has shown positive effects in reducing loneliness and feelings of isolation among older adults via social interaction and constructively spending time [
27]. In addition to psychosocial benefits, participating in mentally stimulated leisurely activities may promote stability or enhance cognitive performance. A recent study found that poorer hearing function may affect verbal memory performance and attention to auditory stimuli among older adults [
28], while another study focusing on the association between leisurely activity and cognitive function in old age indicated that more participation in self-improvement, intellectual, or cultural activities was associated with better performance in verbal ability and memory [
29]. Maintaining a moderate or high level of participation in leisurely activities may play a role in the relationship between hearing loss and cognition. Engagement in leisurely activities makes up a considerable amount of daily activity among the Chinese elderly. Leisure activities may be demographically or culturally specific, and studies from Asian countries that have adopted Confucian culture suggested that the link between participating in leisure activities and cognitive performance may differ by sex [
30,
31], as the elderly may possess differences in lifestyle and social networks. Additionally, consequences resulting from hearing loss, as well as the association between specific leisure activity and cognition, may also vary by sex. For example, older men with hearing loss were more likely to be depressed than men with normal hearing, while hearing loss did not affect the odds of depression in older women [
32]. In contrast, elderly women with hearing loss tend to feel socially isolated, however, the association between hearing loss and social isolation was not significant among men [
33]. Cognitively stimulating and socially engaging activities, along with intellectual or cultural activities, were found to reduce the risks of dementia among elderly men and women [
29].
Though much research has documented that hearing loss was associated with cognitive decline and dementia in developed countries, a very limited number of studies have been done in developing countries, and few have focused on the role of engaging in leisurely activity. Maharani et al. [
24] and Frank Lin et al. [
12] put forward that the association between hearing loss and cognitive decline among the elderly may be mediated by cognitive load and/or social isolation. However, whether efforts in maintaining engagement in leisurely activities or increasing the size of social networks may mitigate the impact of hearing loss on cognition are still unclear. Given the expected rise of the aging population in China, a better understanding of such relationships would provide valuable insights into potential approaches in preventing or delaying the onset of dementia. According to the “cognitive load theory” and “cascade hypothesis” [
34], this study aimed to examine: 1) the association of self-perceived hearing loss with cognitive function; 2) the role of engaging in leisurely activities as a potential moderator in this association; and 3) the differences in these associations by sex among the Chinese elderly.
Discussion
This study investigated the association between hearing impairment and cognitive function in a nationwide population-based survey on the Chinese elderly. After identifying the impacts of hearing deprivation on cognitive decline, whether engaging in leisurely activities moderated the link between hearing loss and cognitive function from the perspective of gender was explored. To the best of our knowledge, this is the first study to report the empirical results of hearing loss in relation to cognitive function as well as the moderative role of leisurely activities from a longitudinal survey in mainland China. It was found that elderly males or females who reported as having a self-perceived hearing difficulty had a greater risk of cognitive impairment. Frequent participation in leisurely activities benefited older adults with hearing loss to perform better in cognitive functioning, particularly in the male subgroup.
The results of this study contribute to studies exploring the association between hearing impairment and cognitive function among the aging Chinese population. Our findings align well with those of previous studies [
12,
46,
48], documenting a significant correlation between hearing difficulty and poorer cognitive performance among the elderly. In contrast, other studies have yielded inconsistent findings [
49,
50]. Poorer hearing function may be related to certain domains of cognitive functional decline, especially concerning memory and executive function [
51]. The variability in assessing cognitive function and how one may define hearing loss may result in conflicting findings [
11]. In addition, past studies were conducted in non-representative populations, which may give rise to sample selection bias, leading to inaccurate results.
Previous studies suggested that compared to men, women are more easily affected by the risk factors of cognitive impairment, as women have more rapid declines in hearing sensitivity at certain ranges of frequency [
52], higher CVD (cardiovascular diseases) risks [
53] and an increased likelihood social isolation [
28]. However, our results do not imply sex difference in the association between hearing loss and cognitive impairment.
In the current study, frequent engagement in leisure activities played a moderating role in the association between hearing loss and cognitive decline. Previous studies focusing on the relationship of hearing loss and cognition considered activities engagement or social isolation as a mediator [
23], or only tested the moderator role of hearing aids, length of time with treatment and age [
54], seldom regarding the activity engagement on the association between hearing health and cognition. Communication breakdown caused by hearing loss may affect the types and frequency of leisure activities that older adults participate in. Hearing-impaired older adults may have to cope with verbal challenges and anxiety stress in the presence of social gatherings. Therefore, performance of auditory function may affect older adults’ engagement in some social activities and hearing-related recreational activities (e.g. listening to music and watching television), which have been proved with cognitive benefits [
55,
56]. Moreover, hearing loss may give rise to basic and instrumental activities of daily living loss [
57]. Engagement in productive activities, such as caregiving or doing housework, may require hearing-impaired older adults more cognitive capacity to deal with complex cognitive tasks. Leisure activities involve physical, mental, and social components [
58]. Compared to productive activities, engagement in leisure activities, such as personal slow walking or outdoor exercising, may require less cognitive loads or social interaction burden. Active participated in leisure activities, such as reading or knitting, can benefit hearing-impaired older adults’ cognition by fostering intellectual stimulation, mood improvement that are related to cognitive maintenance [
59].
Sex difference is shown in the moderating effect of leisure activities between hearing loss and cognitive decline. Although frequent engaged in leisure activities mitigated the effects of hearing loss on cognitive decline among older males, we did not find any statistically significant association between the interaction of various types of leisure activities on hearing loss and cognition among the female sample. The moderating effect of leisure activities is more pronounced among older men than women may be because women in China tend to have lower education and less likely to accumulate socioeconomic resources [
60], thus resulting in fewer cognitive resources and less benefit from intelligence stimulating activities, such as reading books or magazines. Additionally, older women are generally more likely to sedentary or less active in leisure-time physical activity than men. Older women may perceive more barriers to outdoor activities than men, especially in a condition of perceived poor health status [
61].
The current study has several important limitations. First, our measurement of hearing loss is based on a dichotomized measure of self-reported hearing loss and verbal cognitive test, which may limit the accuracy of our estimations among older adults due to measurement bias. Although Kiely’s et al. (2012) study documented a moderate association between self-reported and audiometric hearing loss and suggested that self-reported hearing loss may indicate hearing disability, the dichotomized measure of self-reported hearing loss does not provide a very accurate and reliable basis to some extent compared with audiometric hearing loss [
62]. Moreover, self-reported items may also be biased by correlated measurement error or same-source bias, such as age, sex or cognitive function. Third, we do not have data on the duration of hearing loss and severity of hearing loss, thus we are not able to identify the exact impact of hearing loss on cognitive function. Further studies are needed with audiometric measures and sufficient information on hearing function to understand the association of hearing loss and cognitive function. The relatively short follow-up period for self-reported hearing loss and cognition contributes to another potential limitation by increasing the uncertainty of our estimates. A further limitation to our main results may come from the potential bias related to sample attrition due to mortality and loss to follow-up. Approximately 38% of the sample from the wave 2011/12 died or lost to follow-up in wave 2014, which may result in significant bias in our estimations. Although our analysis for missing data suggested that the association between hearing loss and cognitive decline was not differed systematically by the follow-up sample or those known to be deceased (see
Supplementary), some caution is still needed in interpreting these results regarding the limitations mentioned above.
Despite these limitations, strengths of our current are that our results are based on a nationally representative sample, and a longitudinal analysis with fixed-effect model methods to avoid the potentially strong cross-sectional confounding effects and fix problems on time-invariant omitted variables to some extent. If our results are confirmed by a standard audiometric testing protocol and in other independent studies, our findings potentially have important implications in aging health. Our findings show that hearing loss was negatively associated with cognitive decline and of importance to highlight the role of leisure activities engagement in moderating the association. This implies the Chinese policy maker to consider the role of hearing aids and activity participation in cognition or dementia prevention program.
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