Furthering the understanding of olfaction, prevalence of loss of smell and risk factors: a population-based survey (OLFACAT study)

Abstract

Objectives: To investigate olfaction in general population, prevalence of olfactory dysfunction and related risk factors.

Design: Cross-sectional population-based survey, distributing four microencapsulated odorants (rose, banana, musk and gas) and two self-administered questionnaires (odour description; epidemiology/health status).

Setting: The survey was distributed to general population through a bilingual (Catalan, Spanish) newspaper in Catalonia (Spain), on December 2003.

Participants: Newspaper readers of all ages and gender; 9348 surveys were analysed from the 10 783 returned.

Main outcome measures: Characteristics of surveyed population, olfaction by age and gender, smell self-perception and smell impairment risk factors. Terms normosmia, hyposmia and anosmia were used when participants detected, recognised or identified all four, one to three or none of the odours, respectively.

Results: Survey profile was a 43-year-old woman with medium-high educational level, living in a city. Olfaction was considered normal in 80.6% (detection), 56% (recognition/memory) and 50.7% (identification). Prevalence of smell dysfunction was 19.4% for detection (0.3% anosmia, 19.1% hyposmia), 43.5% for recognition (0.2% anosmia, 43.3% hyposmia) and 48.8% for identification (0.8% anosmia, 48% hyposmia). Olfaction was worse (p<0.0001) in men than in women through all ages. There was a significant age-related smell detection decline however smell recognition and identification increased up to fourth decade and declined after the sixth decade of life. Risk factors for anosmia were: male gender, loss of smell history and poor olfactory self-perception for detection; low educational level, poor self-perception and pregnancy for recognition; and older age, poor self-perception and history of head trauma and loss of smell for identification. Smoking and exposure to noxious substances were mild protective factors for smell recognition.

Conclusions: Sense of smell in women is better than in men suggesting a learning process during life with deterioration in older ages. Poor self-perception, history of smell loss, head trauma and pregnancy are potential risk factors for olfactory disorders.

Figure 1

Flow-chart of participants in the OLFACAT (Olfaction in Catalonia) survey.

Figure 2

Evolution of normosmia (smell of all four odours) during lifetime. Smell detection showed a progressive decrease during the lifespan, while smell recognition/memory and identification increased up to the fourth decade of life, continued to plateau throughout the fifth and sixth decades, and declined thereafter. For detection, recognition/memory or identification, normosmia was significantly higher (p<0.0001) in women (blue line) than in men (red line).

Figure 3

Evolution of hyposmia (smell of one to three odours) during lifetime. For detection, hyposmia showed a progressive increase during the life span, while for recognition/memory and identification hyposmia decreased up to the fourth decade of life, continued to plateau throughout the fifth and sixth decades and increased thereafter. For detection, recognition/memory or identification, hyposmia was significantly lower (p<0.0001) in women (blue line) than in men (red line).

Figure 4

Evolution of anosmia (smell of none of the four odours) during lifetime. Anosmia showed a progressive mild increase during the life span but being more significant after the sixth decade of life. For detection, recognition/memory or identification, anosmia was significantly lower (p<0.0001) in women (blue line) than in men (red line), with a maximal difference after the seventh decade of life.