For the most part, people lose some degree of smelling ability as they age. About 25 million people in the United States have some type of olfactory (related to smelling) problem. However, few people are totally without the ability to smell, That is, unless they have had a traumatic experience in life such as a serious head injury.

The Rush University study, led by Robert S. Wilson, studied over one thousand subjects that were 80 years and older. The sujects took several smell-recognition tests. Over a ten year period, as these subjects died, the team analyzed, during autopsies, the cell-fiber tangles in the brain (which is a distinctive sign of Alzheimer’s disease).

The first 129 patients showed that the more problems they had identifying smells, the greater the number of cell-fiber tangles in the olfactory area of the brain. Such a relationship in older people, as Wilson states, shows that "problems in smell ability may be a very early sign of [Alzheimer's] disease." [subscription required for online article]

The Rush University study, whose collaborators include Wilson, along with S.E. Arnold, J.A. Schneider, Y. Tang, and D.A. Bennett, is found in the January 2007 issue of the Journal of Neurology, Neurosurgery, and Psychiatry. The article is entitled “The relationship between cerebral Alzheimer's disease pathology and odour identification in old age.” The abstract is found at: http://jnnp.bmj.com/cgi/content/abstract/78/1/30.

Further studies in this area hope to develop a test involving smell that would help identify people with early signs of neurological problems such as Alzheimer’s disease.

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