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Clínic Barcelona

One in five people suffer from olfactory dysfunction

The sense of smell may seem secondary but it provides information on the surrounding environment, warns us about chemical dangers and putrid food and may even help people to mate. It is important to be aware of our olfactory capabilities not only to enjoy food and aromas but also to notice potentially harmful chemicals and gases. The statistical analysis of OLFACAT, a study performed in December 2003, arrives now to the scientific community through an article published in the British Medical Journal (BMJ). It consisted in a cross-sectional population-based survey, distributed to general population through a bilingual Catalan - Spanish newspaper, and was coordinated by Dr. Joaquim Mullol, Senior researcher at Institut d’Investigacions Biomèdiques August Pi i Sunyer (IDIBAPS) and director of the Rhinology Unit and Smell Clinic at the Department of Otorhinolaryngology of the Hospital Clínic of Barcelona, in collaboration with the Hospital Municipal de Badalona. The results show that almost one in five people in the general population suffer a certain level of olfactory dysfunction and determines the main risk factors for anosmia (total loss of sense of smell) and hyposmia (partial loss of smell).

With more than 10.000 participants (9.348 included in the data analysis) it is the largest European study about olfaction in general population. The survey consisted of four microencapsulated odorants (rose, banana, musk and gas) and two self-administered questionnaires on odour perception and epidemiology/health status. The terms normosmia, hyposmia and anosmia were used when participants detected, recognised or identified all four, one to three or none of the odours, respectively.

The results of the statistical analysis show, in accordance with other studies, that women performed better in olfactory tasks compared with men of the same age group as well as self-reporting a better perception of smell sense. This gender difference was maintained across the lifespan, and increased considerably after the seventh decade of life. 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 memory/recognition (0.2% anosmia, 43.3% hyposmia) and 48.8% for identification (0.8% anosmia, 48% hyposmia). Finally, 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. The study also suggests a learning process to smell during life related correlated with the educational level of participants.

In conclusion, olfactory dysfunction in general population is a condition far more extended than previously reported. The OLFACAT study estimates that 1.2 million adult Catalans, 7.7 million Spaniards and over 82 million EU citizens suffer from olfactory dysfunction, of which 20,000 Catalans, 120,000 Spaniards and 1.5 million EU citizens have a total loss of sense of smell. The study also determines the main risk factors for anosmia: male gender, loss of smell history and poor olfactory self-perception for detection; low educational level, poor olfactory self-perception and pregnancy for memory/recognition; and older age, poor olfactory self-perception and history of head trauma and loss of smell for identification. Surprisingly, smoking and exposure to noxious substances were mild protective factors for smell memory/recognition.