Writing in the Annals of Internal Medicine, researchers in the USA and Sweden report how more than 2,200 people aged between 71 and 82 undertook smell identification tests near the turn of the millennium, which were then followed up over 13 years.
Epidemiologist Honglei Chen says the study is the first to explore potential reasons for why a poor sense of smell, which becomes more common as people age, is associated with an increased risk for death.
People who eat poorly due to their lost sense of smell might also be at higher risk of developing heart disease, due to malnutrition or by eating unhealthy junk foods that have a vivid taste, Chen added.
They discovered that a poor sense of smell was associated with a almost 50% higher risk of death within the next decade for adults older than 70.
Elderly people with a poor sense of smell have a higher likelihood of dying in the 10 years after testing than those whose sniffers stay sharp.
Poor sense of smell was also strongly linked to death from dementia, Parkinson's disease and weight loss.
'It tells us that in older adults, impaired sense of smell has broader implications of health beyond what we have already known.
Further analysis revealed that poorer olfaction was not associated with death caused by respiratory conditions or cancer, but was significantly associated with death caused by Parkinson's disease and dementia. That includes 22% of the risk attributable to neurodegenerative diseases, and 6% linked to weight loss, researchers reported. "On the other hand, poor olfaction among older adults with excellent to good health may be an early warning sign for insidious adverse health conditions that eventually lead to death", the authors write.
The connection between a poor sense of smell and mortality risk didn't appear to differ by sex or race or based on individuals' demographic characteristics, lifestyle, and or chronic health conditions. There was also a modest association between increased mortality risk and cardiovascular disease.
"We have known for many years that loss of sense of smell in later life may precede other symptoms of neurodegenerative disorders such as Parkinson's or Alzheimer's by many years", he said. "Incorporating a sense of smell screening in routine doctor visits might be a good idea at some point." explains Chen.
"The take-home message is that a loss in the sense of smell may serve as a bellwether for declining health", said Vidyulata Kamath of the Johns Hopkins University School of Medicine in Baltimore, co-author of an accompanying editorial. What's more, the apparent link between the sense and mortality could be down to factors that affect both but were overlooked.
Impaired smell sense may flag up deteriorating health before it is recognised by doctors, scientists believe.