This 13 year study which is published in the journal Annals of Internal Medicine involved 2,289 participants between the ages of 71-82 who were otherside healthy but had an impaired sense of smell who were tasked to complete a smell test of 12 common odors; depending on results participants were rated as having either good, moderate, or poor sense of smell.
By the 13th year nearly half of the participants had died; those who had poor olfactory functions who had difficulty recognizing common odors were found to be 46% more likely to die within the next 10 years with a 30% increase risk by year 13. Lifestyle and demographic factors such as gender and race did not affect the results, but many participants who were healthy at the start of the study were found to be largely responsible for the higher risks.
According to the researchers a poor sense of smell is already a possible indicator of weight loss, dementia and Parkinson’s disease but this only explained 28% of the increased mortality risk: 22% for neurodegenerative diseases and 6% for weight loss, leaving most of the increase unexplained.
“We don’t have a reason for more than 70 percent of the increased risk,” said Honglei Chen, an epidemiologist and one of the researchers. “We need to find out what happened to these individuals.” Chen said they plan to pursue this mystery in the future with more studies. “It tells us that in older adults, impaired sense of smell has broader implications of health beyond what we have already known.”
Chen suggests that including a screening test for sense of smell should become routine at checkups as it may help to provide a better understanding of patient condition, and Robert Howard of the University College London concurred with Chen’s conclusions that olfactory deterioration should be taken more seriously as a marker.
Howard also cautioned “the trouble with any observational research like this is that it’s impossible to be sure about what’s causing what,” which is inline with the team’s sentiment on the 70% increased risk in deteriorating sense of smell being unaccounted for. Howard remarks that there are many differences between those with bad to good sense of smell that may be influencing the higher mortality rates and he believes there are two possibilities. 1) Poor sense of smell is a factor that it is an early sign of an underlying illness contributing to the mortality rate; and 2) Having a poor sense of smell is what leads to illness, “perhaps because poor smell affects how food tastes, and therefore might contribute to poor nutrition which could lead to bad health.” Either way Chen and Howard agree additional research is required to determine the role that sense of smell plays in mortality rates among the elderly.
