Prevalence and risk factors of smell dysfunction - a comparison between five German population-based studies

Abstract

Background: The prevalence of olfactory impairment increases with age and is known to be an early sign of different neurodegenerative diseases. Only few population-based studies examined the prevalence of olfactory impairment and comparisons across studies are scarce. Aim of this analysis was to compare the prevalence and determinants of normosmia across five population based studies in Germany.

Methodology: Data from five population-based, cross-sectional studies were included. They were independently conducted and used the same test system (Sniffin' Sticks Screening 12) to measure olfactory function. This system consists of 12 odor-dispensing felt-tip pens; the task is a forced-choice selection among four alternative odors per pen. Sociodemographic information and comorbidities were assessed in face-to-face interviews. Univariate, descriptive statistics and multivariable logistic regression models stratified by study, were performed to determine risks, i.e. prevalence odds ratios, associated with olfactory function.

Results: The prevalence of normosmic participants varied considerably across studies. Olfactory function was lower in men, decreased with age, and increased with higher education. Several individual comorbidities and a comorbidity index were associated with olfactory dysfunction. Recognition performance for three of the 12 pens was especially low in all studies.

Conclusion: Four factors, well known to describe population composition, contribute to explain differences in the prevalence of olfactory function between studies when the same test system is used. Our results indicate that comorbidities and educational level should always be considered when test systems based on smell recognition are used in population-based studies.