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Poor smell sense could signal early Alzheimer’s

July 2, 2007
Asso­ciated Press

Dif­fi­cul­ty iden­ti­fy­ing com­mon smells such as lem­on, ba­nana and cin­na­mon may be the first sign of Alzheimer’s dis­ease, ac­cord­ing to a study that could lead to scratch-and-sniff tests to de­ter­mine a per­son’s risk for the pro­gres­sive brain dis­or­der. 

Such tests could be im­por­tant if sci­en­tists find ways to slow or stop Alzheimer’s and the se­vere mem­o­ry loss as­so­ci­at­ed with it. For now, there’s no cure for the more than 5 mil­lion Amer­i­cans with the dis­ease.

Re­search­ers have long known that mi­cro­scop­ic le­sions con­sid­ered the hall­marks of Alzheimer’s first ap­pear in a brain re­gion im­por­tant to the sense of smell.

“Strictly on the ba­sis of anat­o­my, yeah, this makes sense,” said Rob­ert Franks, an ex­pert on odor per­cep­tion and the brain at the Un­ivers­ity of Cin­cin­nati. Franks was not in­volved in the new stu­dy, ap­pearing in Mon­day’s is­sue of the jour­nal Ar­chives of Gen­er­al Psy­chi­a­try.

Oth­er stud­ies have linked loss of smell to Alzheimer’s, Franks said, but this is the first to meas­ure healthy peo­ple’s ol­fac­to­ry pow­ers and fol­low them for five years, test­ing along the way for signs of men­tal de­cline.

In the stu­dy, 600 peo­ple be­tween the ages of 54 and 100 were asked to iden­ti­fy a doz­en fa­mil­iar smells: on­ion, lem­on, cin­na­mon, black pep­per, choc­o­late, rose, ba­nana, pine­ap­ple, soap, paint thin­ner, gas­o­line and smoke.

For each mys­tery scent, they heard and saw a choice of four an­swers. For cin­na­mon, they were asked aloud: “Fruit? Cin­na­mon? Wood­y? Or co­conut?” while al­so see­ing the choices in text.

A quar­ter of the peo­ple cor­rectly iden­ti­fied all the odors or missed only one. Half of them knew at least nine of the 12. The lowest-scoring quar­ter of the peo­ple cor­rectly iden­ti­fied eight or few­er of the odors.

The sub­jects took 21 cog­ni­tive tests an­nu­ally over the next five years. About one-third of the peo­ple de­vel­oped at least mild trou­ble with mem­o­ry and think­ing.

The peo­ple who made at least four er­rors on the odor test were 50 per­cent more likely to de­vel­op prob­lems than peo­ple who made no more than one er­ror. Dif­fi­cul­ty iden­ti­fy­ing odors al­so was as­so­ci­at­ed with a high­er risk of pro­gress­ing from mild cog­ni­tive im­pair­ment to Alzheimer’s. 

Alzheimer’s is a de­gen­er­a­tive brain dis­ease that usu­ally be­gins grad­u­al­ly, caus­ing a per­son to for­get re­cent events or fa­mil­iar tasks. How rap­idly it ad­vanc­es varies from per­son to per­son, but the dis­ease even­tu­ally leads to con­fu­sion, per­sonal­ity and be­hav­ior changes and im­paired judg­ment. Com­mu­nica­t­ion be­comes more dif­fi­cult as the dis­ease pro­gresses, leav­ing those af­fect­ed strug­gling to find words, fin­ish thoughts or fol­low di­rec­tions. Even­tu­al­ly, most peo­ple with Alzheimer’s dis­ease be­come un­able to care for them­selves. 

The re­search­ers took in­to ac­count age, gen­der, educa­t­ion and a his­to­ry of strokes or smok­ing, and still found low­er scores pre­dicted high­er risk of cog­ni­tive de­cline.

Lead au­thor Rob­ert Wil­son of Chicago’s Rush Un­ivers­ity Med­i­cal Cen­ter said a di­min­ish­ing sense of smell is­n’t cause for pan­ic.

“Not all low scor­ers went on to have cog­ni­tive prob­lems,” Wil­son said.

Old­er peo­ple should re­port a loss in smell to their doc­tors, said Claire Mur­phy, an Alzheimer’s re­search­er at San Die­go State Un­ivers­ity who was not in­volved in the new stu­dy. The prob­lem could be caused by a pol­yp in the nose or in­fected si­nus­es, she said.

“If a per­son is old and has a very good sense of smell, that’s a very good sign,” Mur­phy said.

The study was funded by the Na­tional In­sti­tute on Ag­ing and the Il­li­nois De­part­ment of Pub­lic Health.

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Difficulty identifying common smells such as lemon, banana and cinnamon may be the first sign of Alzheimer’s disease, according to a study that could lead to scratch-and-sniff tests to determine a person’s risk for the progressive brain disorder.