Olfactory function in elderly people and patients with Alzheimer's disease.

Background: Olfactory function is an important sensory perception function that helps us detect the smell of spoiled food, dirty clothing, and gas leaks. If ageing and Alzheimer's disease (AD) are accompanied by a decline in olfactory function, this might reduce the ability to sense danger, placing the safety and hygiene of elderly people at risk.

Methods: Subjects in this study included 113 healthy subjects aged 20-89 years and 12 persons with AD aged 62-85 years. The healthy subjects were divided into three groups according to age: young-adult group (20-43 years), middle-adult group (45-69 years), and old-adult group (70-89 years). The Hasegawa Dementia Scale-Revised score of AD subjects ranged from 15 to 26. We developed and implemented an odour identification ability test and a situational judgement test using an odour stick to examine the impact of ageing and AD on olfactory function from the perspective of sensing danger. To examine the impact of mild AD on the olfactory function, we compared the scores between the AD group and the age-matched control group.

Results: The scores for the situational judgement and odour identification ability tests were significantly lower in an old-adult group than in the young-adult and middle-adult groups. A significant correlation was found between age and scores for both tests in the control group. The AD group exhibited significantly lower total scores on both tests compared with the age-matched controls.

Conclusions: These results suggest that ageing and mild AD may reduce the ability to identify odours and judge situations based on odours.