Aging is correlated with both hearing loss and cognitive decline. “Inner ear hair cells, spiral ganglion cells, and cortical neurons can be lost with aging and generally do not regenerate,” said Joseph Breen, MD, assistant professor of otolaryngology–head and neck surgery at the University of Cincinnati College of Medicine in Ohio. “The long-held assumption has been that the metabolic processes of aging are causative for both cognitive decline and hearing difficulties, but more recent research has explored a direct relationship between these two problems, independent of normal aging.”
Explore This IssueSeptember 2019
Data from the National Health and Nutrition Examination Survey report that more than 50% of adults in their 70s have some degree of bilateral hearing loss, and that number rises to more than 80% for adults 80 and older (Am J Public Health. 2016;106:1820–1822). Researchers found a greater than 20% rate of mild cognitive impairment in adults over 70, in addition to the 5% to 7% of adults in that same age group who have dementia (Alzheimers Dement. 2019;11:248–256).
In 2017, The Lancet International Commission on Dementia Prevention, Intervention, and Care estimated that hearing loss will increase risk for dementia by 94%, with risk escalating as hearing loss severity increases (Lancet. 2017;390:P2673–P2734). “Because so many older adults have hearing loss, prevention or treatment of hearing loss is estimated to have the greatest potential for dementia prevention compared with any other modifiable dementia risk factors,” said Jennifer Deal, PhD, assistant scientist in the departments of epidemiology and otolaryngology–head and neck surgery and core faculty with the Johns Hopkins Cochlear Center for Hearing and Public Health in Baltimore, Md. According to the commission, up to 9% of dementia cases in the world could be prevented if hearing loss were treated; however, this assumes that hearing loss is a cause of dementia, information that is currently unknown.
Sharon G. Curhan, MD, ScM, a physician and epidemiologist with Brigham and Women’s Hospital and Harvard Medical School in Boston, and her colleagues examined the longitudinal relationship between hearing loss and a decline in subjective cognitive function, a measure that appraises cognitive concerns that reflect changes in memory or thinking experienced by an individual who may not demonstrate abnormal performance on standard cognitive tests (Alzheimers Dement. 2019;15:525–533). “A decline in subjective cognitive function may capture an individual’s self-perceived experience of cognitive decline before cognitive impairment becomes apparent on clinical neurocognitive tests and may be an early manifestation of preclinical dementia,” she said. The eight-year study examined 10,107 men aged 62 and older.
The researchers found that hearing loss was associated with higher risk of subjective cognitive function (SCF) decline, Dr. Curhan said. Compared with men who did not experience hearing loss, the multivariable-adjusted relative risk of incident SCF decline was 30% higher among men with mild hearing loss, 42% higher among men with moderate hearing loss, and 54% higher among men with severe hearing loss who didn’t use hearing aids. Among men with severe hearing loss who did use hearing aids, the risk was somewhat attenuated (37% higher) but wasn’t statistically significantly different from the risk among those who didn’t use hearing aids.