Older people who can actually smell roses may have a lower risk of dementia, research suggests.
Scientists from the University of California, San Francisco (UCSF), followed 1,800 people in their seventies for up to 10 years.
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They found that those who retained good sensory function, including the ability to identify the scent of roses, paint thinners, and lemons, were up to half as likely to develop memory-stealing disease.
As for why this occurs, scientists wondered if parts of the brain affected by dementia can also regulate our sense of smell.
Sensory decline itself can also trigger memory loss, possibly indirectly by hindering socialization or affecting mental health.
Dementia is a general term for conditions that cause progressive loss of brain function.
Around 850,000 people live with the disease in the UK.
In the United States, 5.7 million people are said to have dementia.
UCSF scientists set out to discover whether sensory function is related to the disease, and previous studies suggest an association.
At the start of the study, all participants were free of dementia, with 328 (18%) developing the condition over the next decade.
After ranking the participants’ sensory levels, the scientists found that 27% of those with a low score were diagnosed with dementia.
This compares with 19% in the mid-range and 12% with a “good” score.
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In addition to the smell, the scientists also considered hearing, vision, and touch.
The odor, tested by identifying distinctive odors such as onion and turpentine, was found to have the greatest impact.
Participants whose sense of smell decreased by 10% had a 19% increased risk of developing dementia, compared with a 1% to 3% increased chance for those who had the same decrease in vision, hearing, or touch.
“The olfactory bulb, which is critical to smell, is affected quite early in the course of the disease,” said lead author Dr. Willa Brenowitz.
“Smell is believed to be a preclinical indicator of dementia, while hearing and vision may have a greater role in promoting dementia.”
Scientists have suggested that sensory impairment may be due to “underlying neurodegeneration or the same disease processes as those that affect cognition, such as stroke.”
“Alternatively, sensory deficits, particularly hearing and vision, can accelerate cognitive decline, either directly impacting cognition or indirectly by increasing social isolation, poor mobility, and adverse mental health,” said Dr. Brenowitz.
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It was even found that an apparently minor loss of sensory function increases the risk somewhat.
“We found that with impaired multisensory functioning, the risk of cognitive decline increased in a dose-response fashion,” said study author Dr. Kristine Yaffe.
“Even mild or moderate sensory deficiencies in 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 the onset of dementia for intervention”.
The results, published in Alzheimer and Dementia: The Journal of the Alzheimer’s Association, revealed that participants with good multisensory function were generally healthier, with a lower rate of diabetes, heart disease, high blood pressure, or stroke.
They were also more likely to have completed high school.
