Editor's note: The first installment of this two-part article was published in our September 2017 issue.
The number of people with dementia is expected to increase from 41 million in 2015 to 66 million by 2030, and rise to 131 million by 2050 (ADI, 2015). Similarly, the number of hearing-impaired adults aged 60 years and older is expected to rise from 21 million in 2020 to 27 million in 2030, with the most dramatic growth taking place among those with moderate or severe hearing loss (JAMA Otolaryngol Head Neck Surg. 2017;143:733).
Specifically, in 2020 the number of adults 60 years and older with moderate or severe hearing loss is expected to reach 13 million, rising to 18 million by 2030 (JAMA Otolaryngol Head Neck Surg. 2017). This growth in dementia and hearing loss prevalence is driven by the rising number of older adults in the United States and across the world. Both dementia and age-related hearing loss (ARHL) are considered public health problems that are costly to the individuals, their families, and to society. (Lancet. 2017;pii:S0140-673631363).
It's becoming increasingly accepted that the reach of hearing loss extends far beyond sensory impairment; ARHL may either add to the cognitive load of an already vulnerable aging brain, and/or it may contribute to social disengagement, possibly accelerating cognitive decline (Lancet. 2017; pii:S0140-673631073; Lancet. 2017; Psychol Aging. 1994;9:339). In fact, the Lancet International Commission on Dementia Prevention, Intervention, and Care recently extended the list of modifiable risk factors for addressing dementia to include hearing loss (Lancet. 2017).
2017 LANCET COMMISSION REPORT
Authored by 24 international experts on dementia, the Lancet Commission report described in detail the results of their review and meta-analyses of recent advances in dementia research (Lancet. 2017). They proposed mechanisms linking potentially modifiable risk factors to dementia, and projected that close to a third of dementia cases might be preventable at an individual level. While the greatest risk factor for dementia—age—is not modifiable, the other nine risk factors are. These include cardiovascular disease, metabolic and psychiatric factors, diet, lifestyle, education, hearing loss, and social isolation. According to their model, 35 percent of dementia cases can be attributable to the nine modifiable risk factors (Table 1). A threat to morbidity and mortality, social isolation—be it number of social contacts, social participation, or dissatisfaction with the level of social contacts—was also listed as a modifiable risk factor by the U.K. National Institute of Health and Care Excellence (NICE) and the U.S. National Institutes of Health (NIH) guidelines (NICE, 2015; NIH Consens State Sci Statements. 2010;27:1). These highlight social engagement as a necessary condition for successful aging and well-being.
LIFE COURSE APPROACH
The commission suggested that dementia may be a clinically silent disorder that begins at midlife (about age 40–65 years), and hypothesized that a window of opportunity may exist for early intervention by addressing the risk factors in middle age (Lancet. 2017;pii:S0140-673631756). They adopted a life course risk factor approach to possibly disrupt the mechanisms that contribute to dementia onset (Fig. 1). Informed by the data demonstrating the bi-directional link between hearing loss and incident dementia, the authors consider hearing loss to be a mid-life risk factor (PLoS One. 2016;11:e0156876; Aging Ment Health. 2014;18:671). They reasoned that hearing loss may add to the cognitive load of an aging brain (cognitive load hypothesis) or it may lead to social isolation (cascade hypothesis), which is associated with faster cognitive decline and depression (Lancet. 2017;pii:S0140-67363175; CNS Spectrums. 2017;22:247). The report underscores the connection between social engagement and physical and mental health. A necessary ingredient for social engagement is the ability to communicate and encode spoken language.
HEARING INTERVENTIONS TO THE RESCUE
Several studies have recently explored the connection between hearing interventions (e.g., hearing aids, hearing assistance technologies, and cochlear implants). Notably, available evidence does not support the robust effect of hearing-aid use in protecting against cognitive decline; these devices are not effective at slowing down or reversing cognitive decline (J Alzheimers Dis. 2017;58:123; J Am Geriatr Soc. 2015;63:2099). We do know, however, that by partially restoring communication abilities, hearing aids may serve as a buffer against social and emotional loneliness and depression, thereby improving the patients’ mood, boosting the quality and quantity of their social interactions, and enabling their participation in cognitively-stimulating activities (J Am Geriatr Soc. 2015; PLoS One. 2015;10:e0119616; Am J Audiol. 2016;25:54). Further more, in their pilot study on hearing interventions (including rehabilitation, e.g., Williams Sound Pocketalker®, Sound World Solutions® CS-50) for people with dementia, Mamo, et al., demonstrated that addressing hearing problems in patients with dementia improves communication, which can potentially reduce some of the patient's behavioral symptoms as well as the caregiver's burden (Am J Geriatr Psychiatry. 2017;25:91).
Audiologists have access to interventions designed to increase auditory brain input to help improve social communication and possibly reduce the cognitive load associated with hearing loss and its costly psychosocial consequences. Clinical care of people with hearing loss should include vigilance when addressing memory complaints from patients or caregivers, changes in communication behaviors of our patients, and expressed feelings of loneliness or dissatisfaction with the frequency, quality, and closeness of contacts with family and friends.
When it comes to our interventions (technology and counseling-based rehabilitation), the conversation must be reframed. The goals of hearing rehabilitation should be to increase audibility and improve speech understanding in noise, thereby easing the effort involved in communication to maximize socio-environmental interactions and sustain engagement in social and leisure activities. Table 2 shows the hearing loss prescription (HELP) for people with dementia to help in maintaining social ties. As a social species, humans are affected by social stressors, and need supportive social connections. The ability to hear and communicate effectively is vital to achieving these ends.