Eau d'Aging

The ability to smell declines with age, which makes people vulnerable to health and nutritional problems and might also presage neurodegenerative disorders such as Alzheimer's disease. Researchers are working to understand why olfaction wanes, but a simple awareness of growing smell-less-ness can help the elderly stay healthy and happy.

Everyone knows that the older people get, the more likely they will need glasses. But as the decades roll by, the ability to taste also drops below 20/20. Yet hardly anyone notices.

Some 14 million Americans have trouble smelling, estimates Claire Murphy, a neuropsychologist at San Diego State University in California. And more than half of them don't know it. In a 2002 study, she and her colleagues asked 2500 people how well they could smell different odors. About 10% of the participants, aged 50 to 90, admitted to difficulty. Then she tested them. The 50-year-olds were good judges of their noses--10% couldn't identify all the bouquets. But the older volunteers were way off. More than 60% of those over 80 had sniffers that weren't up to snuff.

Researchers aren't sure why people don't notice the change. Perhaps the loss is too gradual. If old people notice their deficit, "then their loss is pretty major," says Registered Dietitian Valerie Duffy of the University of Connecticut, Storrs.

Serious olfactory impairment is dangerous. People with shoddy snouts run double the risk of finding themselves in sometimes life-threatening situations, say researchers. They might fail to notice gas leaks or burning pots or pans while cooking. And they could have trouble detecting when food goes bad, causing them to wolf down treats that even the dog would reject.

An inability to smell--and thus, to taste flavors beyond salty or sour--can also affect a person's health longer term. People who can't taste can suffer from what Murphy calls "disordered nutrition": Some eat less; others feast excessively. Some who overeat are trying to compensate for the fact that meals no longer bring them pleasure. "They hope that the next bite will taste better," Duffy says.

Duffy interviewed 80 seniors, all women, who lived alone. She asked about their eating habits and tested their ability to smell. Those with poor whiffers gorged on dishes that were sweeter and higher in fat than their able-nosed peers did--and were more likely to be overweight.

Undereating is also a problem for those with a diminished sense of smell. Many elderly people lose interest in food. With fewer calories coming in, they waste away and their immune systems suffer, rendering them more prone to accidents or infection. To combat such ills, psychologist Susan Schiffman of Duke University in Raleigh, North Carolina, has become the nursing-home equivalent of a four-star chef. Her secret ingredient? Concentrated extracts that add a punch of flavor to meals, enough to make up for the deficiencies in the ability to smell of her study volunteers.

"The flavor enhancers make chicken taste more chickeny, potatoes more potatoey, and so on," Schiffman says. Adding enhancers to meals improves the caloric intake of 80-year-olds in long-term-care facilities, she found. In addition, those who chowed power-flavored meals for 3 weeks were more physically fit--they gripped objects with greater force than they did after spending an equivalent amount of time on a standard diet. And the flavorful meals also reinvigorated their immune systems.

An inability to smell could also lead to social exclusion, says Murphy. Some older folks, she notes, "will use a little more cologne or perfume." Such overindulgence in redolence can be a significant problem within the confines of nursing homes.

The research community continues to debate why the elderly lose their sense of smell. Medications, head trauma, repeated bouts of the flu, and inflamed sinuses can all damage the nerves that carry information about odor. Even bad oral health can interfere. Ill-fitting dentures can prevent air from wafting up to the odor receptors located in the back of the nose, impairing the wearer's ability to taste, says Duffy. And aging itself probably also slowly wears down the sense of smell. To find out, scientists need to follow individuals long-term to assess how their olfaction changes over time, she says. Knowing the true source of the deficiency is important because identifying the problem will guide the treatment.

Another more sinister cause of olfactory decay is neurological dysfunction. Alzheimer's disease (AD) and some other neurodegenerative illnesses such as Parkinson's disease knock down a person's ability to detect odors. The brain processes smells and stores memories in two different regions hit early in AD, suggesting that "smell memory" tests might be useful in early diagnoses, says Murphy. In a preliminary study, Schiffman and her colleagues found that people who had family members with AD also had trouble remembering scents they had smelled 10 seconds earlier, even though they had no cognitive defects. The results, she says, suggest that smell deficits might reveal which individuals are at risk.

More research is needed to determine why the ability to smell and taste subsides with age, but that won't happen while people remain oblivious to the changes. "The population isn't aware of the problem, so it hasn't been as well researched" as other medical topics, says Murphy. Spreading the word about the dangers of diminished olfaction should help, she says. In the meantime, Duffy says it's important for everyone--starting before they reach old age--to safeguard olfaction as best they can. Avoiding head trauma associated with falls, for example, could help protect the nerve that serves the nose, which zips right behind the bridge. And avoiding the flu might reduce damage done by the virus. Most losses to scent aptitude can't be rectified. So noticing that flavors and odors are graying along with hair can help people plan strong-smelling meals for better nutrition and keep their eyes on the soup pot, the better not to burn down the house.

Like dwindling eyesight, receding smell and taste seem inevitable, at least for now. So until researchers fix our schnozzes, perhaps we should relish flavors and odors before our senses of taste and smell fade away.

Mary Beckman writes from a small town in southeast Idaho and happily can't remember what big cities smell like.

NIH Taste and Smell Disorders http://www.nidcd.nih.gov/health/smelltaste/index.asp