San Francisco: Elderly people who can smell the roses, turpentine, paint thinner, and lemons, may have a lower risk of dementia, research suggests.
In a study by UC San Francisco, researchers tracked close to 1,800 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 (18 per cent) developed the condition over the course of the study.
Among those whose sensory levels ranked in the middle range, 141 of the 328 (19 per cent) developed dementia. This compares with 83 in the good range (12 per cent) and 104 (27 per cent) in the poor range, according to the study, which was published in Alzheimer's and Dementia: The Journal of the Alzheimer's Association.
The UCSF researchers' focus was on the additive effects of multiple impairments in sensory function, which emerging evidence shows are a stronger indicator of declining cognition.
"Sensory impairments could be due to underlying neurodegeneration or the same disease processes as those affecting cognition, such as stroke," said first author Willa Brenowitz, Ph.D., of the UCSF Department of Psychiatry and Behavioral Sciences, and the Weill Institute for Neurosciences.
"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," Brenowitz added.
While multiple impairments were key to the researchers' work, the authors 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 per cent had a 19 per cent higher chance of dementia, versus a one to three per cent increased risk for corresponding declines in vision, hearing, and touch.
"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," said Brenowitz.
The 1,794 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.
Multisensory testing was done 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 researchers 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.
"We found that with deteriorating multisensory functioning, the risk of cognitive decline increased in a dose-response manner," said senior author Kristine Yaffe, MD, of the UCSF departments of Psychiatry and Behavioral Sciences, Epidemiology and Biostatistics, and Neurology, as well as the San Francisco VA Health Care System.
"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 prior to dementia onset for intervention," the author added.
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 per cent versus 72.1 per cent), had less diabetes (16.9 per cent versus 27.9 per cent), and were marginally less likely to have cardiovascular disease, high blood pressure, and stroke.