Keen sense of smell linked to longer life

Older adults with a poor sense of smell may die sooner than their counterparts who have keen olfactory abilities, a US study suggests.

Researchers asked 2,289 adults, ages 71 to 82, to identify 12 common smells, awarding scores from zero to as high as 12 based on how many scents they got right. When they joined the study, none of the participants were frail: they could walk a quarter mile, climb 10 steps, and independently complete daily activities.

During 13 years of follow-up, 1,211 participants died.

Overall, participants with a weak nose were 46 per cent more likely to die by year 10 and 30 per cent more apt to pass away by year 13 than people with a good sense of smell, the study found.

"The association was largely limited to participants who reported good-to-excellent health at enrollment, suggesting that poor sense of smell is an early and sensitive sign for deteriorating health before it is clinically recognisable," said senior study author Dr. Honglei Chen of Michigan State University in East Lansing.

"Poor sense of smell is likely an important health marker in older adults beyond what we have already known about (i.e., connections with dementia, Parkinson's disease, poor nutrition, and safety hazards)," Chen said by email.

People who started out the study in excellent or good health were 62 per cent more likely to die by year 10 when they had a poor sense of smell than when they had a keen nose, researchers report in the Annals of Internal Medicine.

But smell didn't appear to make a meaningful difference in mortality rates for people who were in fair to poor health at the start of the study.

With a poor sense of smell, people were more likely to die of neurodegenerative and cardiovascular diseases, but not of cancer or respiratory conditions.

Poor sense of smell may be an early warning for poor health in older age that goes beyond neurodegenerative diseases that are often signal the beginning of physical or mental decline, the results also suggest.

Dementia or Parkinson disease explained only 22 per cent of the higher death risk tied to a poor sense of smell, while weight loss explained just six per cent of this connection, researchers estimated. That leaves more than 70 per cent of the higher mortality rates tied to a weak nose unexplained.

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.

One limitation of the study is that the older adult participants were relatively functional, making it possible results might differ for younger people or for frail elderly individuals, the study team writes.

Researchers also only tested smell at one point in time, and they didn't look at whether changes in olfactory abilities over time might influence mortality. Researchers also lacked data on certain medical causes of a weak nose such as nasal surgery or chronic rhinosinusitis that are not related to aging.

"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.

"As we age, we may be unaware of declining olfactory abilities," Kamath said by email. "Given this discrepancy, routine olfactory assessment in older adults may have clinical utility in screening persons at risk for illness, injury or disease for whom additional clinical work-up and/or intervention may be warranted."