Loss of sense of smell - early sign of Alzheimer's

According to a new study older people who have difficulty identifying common odors may be more at risk of developing problems with thinking, learning and memory.

Experts say mild cognitive impairment, a decline in thinking, learning and memory is recognized as a precursor to Alzheimer's disease and a weakened sense of smell could be a sign of the disease.

The study by Dr. Robert Wilson at Rush University Medical Center, Chicago, and colleagues suggests that a difficulty in identifying odors predicts the development of mild cognitive impairment and could be a useful tool for early disease identification.

The study began in 1997 and examined 589 older adults with an average age of 79 who did not have cognitive impairment.

They were given a smell identification test where 12 familiar odors - onion, lemon, cinnamon, black pepper, chocolate, rose, banana, pineapple, soap, paint thinner, gasoline and smoke - were placed under their nose and they were asked to match each odor to one of four possible alternatives.

The participants underwent a clinical evaluation that included a medical history, neurological examination and testing of their cognitive function at the start of the study and again every year for up to five years.

The researchers found that 177 individuals developed mild cognitive impairment and the risk increased as odor identification decreased.

This association remained even when factors such as stroke, smoking habits or other factors that might influence smell or cognitive ability were considered.

Currently there is no cure for Alzheimer's disease, which affects more than 5 million Americans, but early diagnosis and intervention can slow down the progress and help manage the symptoms that are associated with the disease.

Experts say that microscopic lesions are present in the very early stages of the disease and on the basis of anatomy the findings are logical.

The research could in future lead to a sniff test for the early signs of the devastating disease.

The study was funded by the National Institute on Aging and the Illinois Department of Public Health and is published in the current issue of the Archives of General Psychiatry, one of the JAMA/Archives journals.