This article is more than 5 years old. Information may no longer be current.

Impaired senses may increase risk for dementia, Alzheimer’s disease

Patients who had a combination of impairment to vision, hearing and smelling were at increased risk for Alzheimer’s disease or dementia, according to study findings presented at the Alzheimer’s Association International Conference.

A separate study indicated that impaired sense of smell on particular odors may predict risk for dementia later in life.

Multiple sensory impairment

Few studies have examined the impact of combined visual and hearing sensory impairment on risk for dementia and Alzheimer’s disease according to Willa D. Brenowitz, PhD, MPH, a postdoctoral researcher at the University of California, San Francisco, and colleagues.

They analyzed 1,810 black and white adults aged 70 to 79 years who did not have dementia at study enrollment. Vision, hearing, smell and touch were scored every 3 to 5 years, while incident dementia during the following 10 years was determined based on a combination of clinically significant cognitive decline in Modified Mini-Mental State Exam scores, hospitalization records and dementia medications.

Researchers found that a decreased multisensory score was strongly associated with rates of decline in the Modified Mini-Mental State Exam Score and higher risk for dementia (P < . 001). The average total sensory function score was 6, with worse multisensory scores linked to increased age, being male, white and/or a smoker and worse baseline cognition. Also, a four-point change in score was linked to a 1.68 times higher adjusted HR for dementia (95% CI,1.31-2.01) and an annual decline of 0.24 points on the Modified Mini-Mental State Exam (95% CI, –0.36 to –0.12). In addition, the risk for dementia was 6.8 times higher when comparing the worst quartile of multisensory function score to the best (95% CI, 2.39-19.37).

“Sensory function in multiple domains can be measured during routine health care visits using non-invasive or minimally invasive tests. In addition, some forms of hearing and vision loss can be treated or corrected, which provides potential opportunities for intervention. However, we need more research to determine if treatment or prevention of sensory impairments could reduce risk of dementia,” Brenowitz said in a press release.

In another study, Phillip Hwang, MPH, a doctoral epidemiology student at the University of Washington and colleagues analyzed the association between hearing and vision impairment and risk for Alzheimer’s or other dementia in 2,827 patients older than 75 years who did not have dementia at study enrollment.

They found that the number of sensory impairments was associated with risk of all-cause dementia and Alzheimer’s disease (P < .001). For all-cause dementia, adjusted HR was 1.27 (95% CI, 1.02-1.59) in patients with either hearing or visual difficulty and 1.7 (95% CI, 1.18-2.45) in patients with both visual and hearing impairment compared to patients with no sensory loss. The aHRs for Alzheimer’s disease were 1.29 (95% CI, 1.02-1.62) for single difficulty and 1.69 (95% CI, 1.15-2.49) for dual impairment vs. no sensory impairment.

“Assessment of visual and hearing function may help identify older adults at high risk of developing dementia,” Hwang said in a press release.

Darren M. Lipnicki, PhD, of the Centre for Healthy Brain Ageing in Sydney, and colleagues investigated whether the inability to recognize particular odors foretold future dementia and mortality risk.

Their cohort consisted of 649 patients without dementia at baseline. Patients’ mean age was 78.5 years and 56.9% were women. Current smokers and individuals with smell loss after nasal surgery were excluded. Patients completed the 12-item Brief Smell Identification Test at baseline and were then followed for 6 years.

Lipnicki and colleagues found lower test scores predicted both dementia and mortality in all examined cohorts. Wrong answers to six test items were significantly associated with dementia and/or mortality in adjusted analyses. Inability to recognize smoke, paint thinner, pineapple, gasoline and onion predicted dementia (OR = 0.553; 95% CI, 0.317-0.962) while not recognizing smoke, gasoline, soap and onion predicted mortality (OR = 0.387, 95% CI=0.189-0.793).

“The olfactory system is particularly susceptible to Alzheimer’s pathology,” Lipnicki and colleagues wrote. “However, the sharing of some predictive odors suggests a common mechanism linking smell loss to both future dementia and mortality. This could include environmental exposure and cholinergic modulation given both dementia and mortality have been previously associated with anticholinergic burden.” ­– by Janel Miller

References:

Brenowitz WD, et al. Multisensory impairment and dementia: Worsening function in multiple senses is associated with dementia and cognitive decline.

Hwang P, et al. Dual sensory impairment in older adults and risk of dementia and Alzheimer’s disease.

Lipnicki D, et al. Failure to identify particular odors predicts future dementia and mortality

All presented at: Alzheimer’s Association International Conference. July 14-18, 2019; Los Angeles.

Disclosures: Healio Primary Care was unable to determine the authors’ relevant financial disclosures prior to publication.