Loss of Smell Linked to Alzheimer’s Disease

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Loss of Smell Linked to Alzheimer’s Disease

Rallie McAllister, M.D., M.P.H.

A simple scratch-and-sniff test may help doctors identify patients at risk for Alzheimer’s disease. The results of a study published in JAMA suggest that folks who have difficulty identifying familiar smells including cinnamon, lemon, and gasoline are more likely to develop the degenerative brain disorder. 

Researchers at Rush University Medical Center in Chicago asked nearly 600 adults between the ages of 54 and 100 to sniff and identify a dozen common scents, including black pepper, pineapple, paint thinner, soap, onion, lemon, cinnamon, gasoline, smoke, rose, banana, and chocolate. Over the following five years, the subjects also completed a number of cognitive tests designed to track changes in memory and thinking skills. 

Subjects who made at least four errors on the sniff tests were 50 percent more likely to develop problems with thinking and memory than subjects who made no more than one error. Trouble identifying familiar odors was also linked to a greater likelihood of advancing from a state of mild cognitive impairment to Alzheimer’s disease. 

Identifying odors is a complex process that involves first perceiving a particular smell and then comparing it against the brain’s memory bank of smells. Alzheimer’s disease gradually robs individuals of their memories; even those for various odors. 

Scoring poorly on a scratch-and-sniff test may be suggestive of Alzheimer’s disease in some cases, but the inability to recognize certain odors often has a far less ominous cause. Disorders of smell are relatively common in the general population, especially among older adults. 

As many as half of folks aged 65 and older are thought to suffer some loss of their sense of smell. The most common causes are upper respiratory tract infections, head trauma, and nasal and sinus disorders, including allergies and chronic sinusitis. 

Certain medications, illnesses, and nutritional deficiencies can also contribute to smell disturbances. Cigarette smoking may dull the senses to some degree, but rarely causes a complete loss of smell.

While a scratch-and-sniff test can’t provide a definitive diagnosis of Alzheimer’s disease, it’s a tool that many doctors will likely find useful. 

Using currently available diagnostic tests, physicians can diagnose individuals with moderate to severe Alzheimer’s disease with about 90 percent accuracy. Making the diagnosis in the early stages of the illness, however, is far more difficult. 

Early diagnosis of the disease is becoming increasingly important, as new and more effective treatments are introduced. Identifying Alzheimer’s in its earliest stages also helps patients and their families plan for the future. 

For folks who are determined to avoid Alzheimer’s disease, taking a supplement containing the B-vitamin folate might help. The results of a University of California, Irvine study suggest that older Americans whose total daily folate intake is at or above the recommended dietary allowance could dramatically cut their chances of developing the disease. 

At the start of the study, researchers collected dietary information from more than 500 healthy volunteers aged 60 and older who showed no signs of Alzheimer’s disease. The subjects recorded the foods they ate during a typical week and reported whether they took supplements containing folate. 

Study participants who reported folate intakes that were equal to or greater than the recommended daily allowance of 400 micrograms had a 55 percent reduction in the risk of Alzheimer’s disease. Although folate is present in many foods, most of the subjects who achieved the recommended daily intake levels did so by taking folate supplements. 

Good sources of the vitamin include leafy green vegetables, broccoli, asparagus, and many varieties of beans and peas. Folate is also found in liver, strawberries, oranges, and a number of vitamin-fortified breads and cereals. 

Eating a nutritious diet and taking a daily folate supplement may help ward off degenerative brain diseases, and getting plenty of physical and mental exercise appears to be just as important.

Physical activity enhances blood flow to the brain, improving its function. Challenging the brain by working puzzles and learning new skills can boost cognitive reserve, or the ability to withstand the damaging effects of Alzheimer’s disease for longer periods of time. 

For older adults, staying socially engaged is especially important. Declining social interaction with advancing age is associated with a decline in cognitive function.

While a number of Alzheimer’s drugs are under investigation, few effective treatments currently are available. At this point, preventive measures appear to be the best defense, and the sooner in life they’re started, the better. 


Rallie McAllister, M.D., M.P.H., is a family physician in Kingsport, Tenn., and author of “Healthy Lunchbox: The Working Mom’s Guide to Keeping You and Your Kids Trim.” Her Web site is http://www.rallieonhealth.com. To find out more about Rallie

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