Seniors who can smell roses, lemons or thinners may have lower chances of suffering from dementia, says study
The authors say that a keen sense of smell has a stronger association against dementia than touch, hearing, or vision
Seniors who can identify smells like roses, paint-thinner, lemons, and turpentine, and have retained their senses of hearing, vision, and touch, may have half the risk of developing dementia compared to their peers with a marked sensory decline, say researchers. While multiple impairments were key to the researchers' work, the research team acknowledged that a keen sense of smell, or olfaction, has a stronger association against dementia than touch, hearing, or vision. Participants whose smell declined by 10% had a 19% higher chance of dementia, versus a 1-to-3-percent increased risk for corresponding declines in vision, hearing, and touch.
In the study by the University of California, San Francisco (UCSF), authors tracked nearly 1,794 participants in their seventies for a period of up to 10 years to see if their sensory functioning correlated with the development of dementia. At the time of enrollment, all participants were dementia-free, but 328 participants or 18% developed the condition over the course of the study.
The analysis reveals that among those whose sensory levels ranked in the middle range, 141 of the 328 (19%) developed dementia. This compares with 83 in the good range (12%) and 104 (27%) in the poor range, according to the study published in Alzheimer's and Dementia: The Journal of the Alzheimer's Association. The study was funded by the National Institutes of Health, the National Institute on Aging and the Alzheimer's Association.
“Sensory impairments could be due to underlying neurodegeneration or the same disease processes as those affecting cognition, such as stroke. Alternatively, sensory impairments, particularly hearing and vision, may accelerate cognitive decline, either directly impacting cognition or indirectly by increasing social isolation, poor mobility and adverse mental health,” writes first author Dr Willa Brenowitz, UCSF Department of Psychiatry and Behavioral Sciences, and the Weill Institute for Neurosciences, in the report. “The olfactory bulb, which is critical for smell, is affected fairly early on in the course of the disease. It's thought that smell may be a preclinical indicator of dementia, while hearing and vision may have more of a role in promoting dementia,” adds Brenowitz.
Alzheimer’s is the most common cause of dementia among older adults. The World Health Organization (WHO) defines dementia as a syndrome — usually of a chronic or progressive nature — in which there is deterioration in memory, thinking, behavior and the ability to perform everyday activities. According to the National Institute on Aging, estimates vary, but experts suggest that more than 5.5 million Americans, most of them aged 65 or older, may have dementia caused by Alzheimer’s. By 2050, the number of people aged 65 and older with Alzheimer’s dementia is projected to rise to 13.8 million, barring the development of medical breakthroughs to prevent, slow or cure Alzheimer’s disease, says the Alzheimer's Association.
For the current study, the participants were recruited from a random sample of Medicare-eligible adults in the Health, Aging, and Body Composition study. Cognitive testing was done at the beginning of the study and repeated every other year. “Dementia was defined by testing that showed a significant drop from baseline scores, documented use of a dementia medication or hospitalization for dementia as a primary or secondary diagnosis,” the findings state.
The team conducted “multisensory testing” in the third-to-fifth year and included hearing (hearing aids were not allowed), contrast-sensitivity tests for vision (glasses were permitted), touch testing in which vibrations were measured in the big toe, and smell, involving identifying distinctive odors like paint-thinner, roses, lemons, onions, and turpentine. The authors found that participants who remained dementia-free generally had “higher cognition” at enrollment and tended to have “no sensory impairments.” Those in the middle range tended to have multiple mild impairments or a single moderate-to-severe impairment. Participants at higher risk had multiple moderate-to-severe impairments, shows analysis.
“Even mild or moderate sensory impairments across multiple domains were associated with an increased risk of dementia, indicating that people with poor multisensory function are a high-risk population that could be targeted before dementia onset for intervention,” says senior author Kristine Yaffe, MD, from the UCSF departments of Psychiatry and Behavioral Sciences, Epidemiology and Biostatistics, and Neurology, as well as the San Francisco VA Health Care System.
Among other findings, the research shows that the 780 participants with good multisensory function were more likely to be healthier than the 499 participants with poor multisensory function, suggesting that some lifestyle habits may play a role in reducing risks for dementia. The former group was more likely to have completed high school (85% versus 72.1%), had less diabetes (16.9% versus 27.9%), and were marginally less likely to have cardiovascular disease, high blood pressure, and stroke, says the team.