Decreased ability to identify odors may predict 5-year mortality

For older adults, being unable to identify scents may be a predictor of mortality within five years, according to a study published October 1, 2014, in the journal PLOS ONE by Jayant Pinto from The University of Chicago and colleagues.

The study was part of the National Social Life, Health and Aging Project (NSHAP), the first in-home study of social relationships and health in a large, nationally representative sample of men and women ages 57 to 85. Researchers first surveyed 3,000 participants in 2005-06, assessing their ability to identify five distinct common odors, one at a time, from a set of four choices. The five odors, in order of increasing difficulty, were peppermint, fish, orange, rose and leather. In the second survey, during 2010-11, the team confirmed which participants were still living. During that five-year gap, 430 (12.5%) of the original 3005 study subjects had died; 2,565 were still alive.

Thirty-nine percent of study subjects who failed the first smelling test died before the second survey, compared to 19 percent of those with moderate smell loss and just 10 percent of those with a healthy sense of smell. For those already at high risk, lacking a sense of smell more than doubled the probability of death. When the researchers adjusted for demographic variables such as age, gender, socioeconomic status (as measured by education or assets), overall health, and race-those with greater smell loss when first tested were substantially more likely to have died five years later. Precisely how smell loss contributes to mortality is unclear, but olfactory dysfunction was better at predicting mortality than a diagnosis of heart failure, cancer or lung disease. Only severe liver damage was a more powerful predictor of death.

"We think loss of the sense of smell is like the canary in the coal mine," said the study's lead author Jayant M. Pinto, MD, associate professor of surgery at the University of Chicago. "It doesn't directly cause death, but it's a harbinger, an early warning system, that something has already gone badly wrong, that damage has been done. Our findings could provide a useful clinical test, a quick and inexpensive way to identify patients most at risk."

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