Preventing Olfactory Deterioration: Olfactory Training May Be of Help in Older People

Abstract

The olfactory system changes with age.1, 2 It has been reported that 50% of people aged 65 and older and more than 80% of people aged 80 and older have olfactory deficits.1, 3 Because odor identification1, 2 and sensitivity to odors2 decrease with age, older people are more likely to be harmed by fire or poisoned by rotten food.4, 5 Previous studies have proven the usefulness of olfactory training in treating olfactory deficits with varying etiologies.6, 7 The aim of this prospective study was to examine the effect of olfactory training in older people over a period of 3 months. All aspects of the study were performed in accordance with the Declaration of Helsinki. The ethics board of the Faculty of Medicine of the Technical University of Dresden approved the study (protocol EK 4002009). Written informed consent was obtained from all participants. Ninety-one participants (64 female, 27 male; mean age 81 ± 8.6, range 55–96) with a Mini-Mental State Examination score greater than 25 points were included in the study, 43 of whom (46.7%) performed the olfactory training. They were instructed to smell four common odors two times daily (in the morning and evening) for 30 seconds each. The odors were chosen according to previous studies:6, 7 citronellal (lemon), cineol (eucalyptus), phenyl-ethyl-alcohol (PEA; rose), and eugenol (cloves). Forty-eight (52.2%) participants were in the control group. The two groups did not differ regarding mean age (training group, 80.1 ± 7.8; control group, 81.6 ± 9.3; t = 0.81, P = .42) or sex (χ2=1.22, P = .14). The olfactory function of all participants was assessed twice at an interval of 3 months, during which the training group performed the olfactory training, using the 16-item odor identification test and the PEA threshold test from the Sniffin' Sticks battery.8 The control group did not differ from the training group in terms of olfactory function (mean olfactory threshold scores: control 3.71 ± 2.60, training group 4.20 ± 3.32; t = 0.70, P = .48; mean odor identification score: control 8.0 ± 2.8, training group 8.5 ± 3.9, t = 0.68, P = .50). A trend toward significance was observed between the two groups in odor threshold score at the second testing after 3 months (t = 1.69, P = .09). Although the olfactory function of the training group increased slightly, no significant change was seen for the odor threshold (t = 1.44, P = .16) or identification score (t = 0.41, P = .68). Olfactory function in the control group decreased slightly but not significantly. Fifty-two percent of the training group reported having followed the olfactory training protocol as instructed. This subgroup did not differ from the control group before the training in olfactory function (odor threshold score: t = 1.51, P = 0.14; odor identification score: t = 1.79, P = 0.083). After olfactory training, these two groups differed significantly in odor threshold performance (t = 2.32, P = .02) and odor identification scores (t = 2.19, P = .03) (Figure 1). No significant change was observed within the training group. Age and sex did not affect any of the comparisons mentioned above. The effect of olfactory training was observed over a 3-month period in older people. No significant increase in olfactory function was observed in the training group. Nonetheless, the olfactory training group had significantly higher olfactory test scores after the training than the control group. Olfactory training has been shown to improve olfactory function in individuals with hyposmia.6, 7 A benefit of olfactory training for older people has been suggested,2 but no study has previously addressed this topic. There are several possible reasons for the lack of olfactory improvement in the current study. With increasing age, the regenerative ability of the olfactory mucosa decreases, the number of mature olfactory receptor neurons decrease,9, 10 and cell turnover in the olfactory epithelium is slower.9 Taking all this into account, the olfactory system of older people does not seem to be as plastic as that of younger people, so a longer training interval might improve the benefit of olfactory training in older people. Although no significant improvement in olfactory function was observed, olfactory training seems to prevent olfactory deterioration that occurs with age. Conflict of Interest: None of the authors has any conflict of interest to disclose. This research was SPP 1392: DFG HU 441/10–1. Author Contributions: Concept and design: Lehmann, Prange, Hummel. Performance of experiments: Lehmann, Prange. Data analysis: Schriever, Hummel. Writing the paper: Schriever, Hummel. Critical discussion: Schriever, Hummel, Prange, Lehmann. Sponsor's Role: None.