DECREASED ABILITY TO SMELL CAN PREDICT DEATH
For older adults, being unable to identify
scents is a strong predictor of death within five years, according to a study
published October 1, 2014, in the journal PLOS ONE. Thirty-nine percent of study subjects who
failed a simple smelling test died during that period, compared to 19 percent
of those with moderate smell loss and just 10 percent of those with a healthy
sense of smell.
The hazards of smell
loss were "strikingly robust," the researchers note, above and beyond
most chronic diseases. 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. For those already at high risk,
lacking a sense of smell more than doubled the probability 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, an associate professor of surgery at
the University of Chicago who specializes in the genetics and treatment of
olfactory and sinus disease. "It doesn't directly cause death, but it's a
harbinger, an early warning that something has 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."
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.
In the first wave of
NSHAP, conducted in 2005-06, professional survey teams from the National
Opinion Research Center at the University of Chicago used a well-validated test
-- adapted by Martha K. McClintock, PhD, the study's senior author -- for this
field survey of 3,005 participants. It measured their ability to identify five
distinct common odors.
The modified smell
tests used "Sniffin'Sticks," odor-dispensing devices that resemble a
felt-tip pen but are loaded with aromas rather than ink. Subjects were asked to
identify each smell, 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.
Measuring smell with
this test, they learned that: • Almost 78 percent of those tested were
classified as "normosmic," having normal smelling; 45.5 percent
correctly identified five out of five odors and 29 percent identified four out
of five. • Almost 20 percent were considered "hyposmic." They got two
or three out of five correct. • The remaining 3.5 percent were labelled
"anosmic." They could identify just one of the five scents (2.4%), or
none (1.1%).
The interviewers
also assessed participants' age, physical and mental health, social and
financial resources, education, and alcohol or substance abuse through
structured interviews, testing and questionnaires. As expected, performance on
the scent test declined steadily with age; 64 percent of 57-year-olds correctly
identified all five smells. That fell to 25 percent of 85-year-olds.
In the second wave,
during 2010-11, the survey team carefully confirmed which participants were
still alive. During that five-year gap, 430 (12.5%) of the original 3005 study
subjects had died; 2,565 were still alive.
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. Even mild smell loss was associated with greater risk.
"This
evolutionarily ancient special sense may signal a key mechanism that affects
human longevity," noted McClintock, the David Lee Shillinglaw
Distinguished Service Professor of Psychology, who has studied olfactory and
pheromonal communication throughout her career.
Age-related smell
loss can have a substantial impact on lifestyle and wellbeing, according to
Pinto, a member of the university's otolaryngology-head and neck surgery team.
"Smells impact how foods taste. Many people with smell deficits lose the
joy of eating. They make poor food choices, get less nutrition. They can't tell
when foods have spoiled or detect odors that signal danger, like a gas leak or
smoke. They may not notice lapses in personal hygiene."
"Of all human
senses," Pinto said, "smell is the most undervalued and
underappreciated -- until it's gone."
Precisely how smell
loss contributes to mortality is unclear. "Obviously, people don't die
just because their olfactory system is damaged," McClintock said.
The research team,
which includes biopsychologists, physicians, sociologists and statisticians, is
considering several hypotheses. The olfactory nerve, the only cranial nerve
directly exposed to the environment, may serve as a conduit, they suggest,
exposing the central nervous system to pollution, airborne toxins, pathogens or
particulate matter.
McClintock noted
that the olfactory system also has stem cells which self-regenerate, so "a
decrease in the ability to smell may signal a decrease in the body's ability to
rebuild key components that are declining with age and lead to all-cause
mortality."
Comments
Post a Comment