ARE YOU CONSCIOUS OF ANY AGE‐RELATED TASTE IMPAIRMENT? PREVALENCE OF AND FACTORS ASSOCIATED WITH TASTE IMPAIRMENT IN JAPAN

To the Editor: The aging of the world's population has increased public interest in age-related sensory impairments, because various studies have shown that they are associated with poor quality of life.1–4 As with visual, hearing, and olfactory functions, age-related impairment is also reported in the sense of taste.5 Taste impairment negatively affects the well-being of older adults, because this sense is directly related to food intake,1 but few community-based epidemiological studies of age-related taste impairment have been conducted, and even such basic statistical data as its prevalence in the general population are sparse.2,6 Sensory impairments are thought to overlap frequently,3,6,7 but the prevalence of taste impairment in association with other sensory impairments is undetermined. Additionally, if overlaps occur, the various sensory impairments are likely to share some risk factors. Revealing the modifiable common risk factors should help in the development of preventive strategies for taste impairment, as well as other sensory impairments. The prevalence of age-related taste impairment and its proportion of occurrence in combination with other sensory impairments was investigated; the factors associated with taste impairment in Japanese adults was also investigated. This cross-sectional study was conducted in February and March 2010 in a rural mountainous area (Koumi Town, Nagano Prefecture) approximately 120 km northwest of Tokyo. A self-administered questionnaire was distributed to all residents aged 40 and older, 2,791 of whom responded (response proportion 85%). Those who did not answer the questions on sensory impairments were excluded, leaving 2,741 subjects (1,255 men; 1,486 women) for analysis. The institutional review board of Keio University School of Medicine approved the study protocol. Internationally accepted tools to assess taste impairment are scarce,7 so the questionnaire simply asked: “Are you conscious of any age-related taste impairment?” Response options were yes and no. Vision, hearing, and olfactory impairments were evaluated in the same way. Information on smoking habits (never, past, current), alcohol consumption (never, past, current), and educational level (junior high, high, college or higher) was also collected. Body mass index (categorized as <18.5, 18.5–24.9, ≥25.0 kg/m2) was calculated from self-reported height and weight. History of hypertension, diabetes mellitus (DM), stroke, myocardial infarction or angina pectoris, and cancer was ascertained using yes-or-no questions in the following format: “Have you ever been told by a physician(s) that you had …?” The prevalence of taste and other sensory impairments was calculated according to age (5-year intervals) and sex. To clarify the factors associated with taste impairment, a logistic regression model was used, adjusting for age and sex. Odds ratios (ORs) with 95% confidence intervals (CIs) of taste impairment were calculated after adjustment for all factors identified as being associated with taste impairment in the age- and sex-adjusted analyses (P<.20). All analyses were performed using Stata version 11 software (Stata Corp., College Station, TX). The most prevalent impairment, regardless of age or sex, was vision, followed in order by hearing, olfaction, and taste (Figure 1). The overall prevalence of taste impairment was 13.3%, with no significant difference according to sex; prevalence increased with age (from 4.6% in those aged 40–44 to 30.4% in those aged ≥85; P for trend <.001, Cochran-Armitage trend test). Most subjects with taste impairment had comorbid impairments (vision, hearing, and olfaction, 65.9%; vision and hearing, 10.1%; vision and olfaction, 6.1%; hearing and olfaction, 2.5%; vision, 8.9%; hearing, 0.3%; olfaction, 0.8%). Thus, only 5.4% of subjects had taste impairment alone, whereas 75.3% had concomitant impairment of the other “chemical” sense,1 olfaction. Prevalence of taste and other sensory impairments according to age (5-year-intervals) and sex in Japan. After adjusting for age, sex, and all factors associated with taste impairment (history of hypertension, DM, myocardial infarction or angina pectoris, and alcohol consumption), age (OR for 1-year increase=1.05, 95% CI=1.04–1.06) and history of DM (OR=1.61, 95% CI=1.13–2.30) were found to be independently associated with taste impairment. This finding is compatible with those of clinical studies that have frequently associated taste impairment with DM.8 Recent evidence also suggests that DM is associated with hearing, olfactory, and vision impairments.9,10 Taken together, aging and DM might be the major factors in the overlapping of sensory impairments. A clear association between DM and multisensory impairment, defined as three or more sensory impairments, was observed in this study (multiadjusted OR=1.48, 95% CI=1.04–2.11). It is possible that such complications of DM as microvascular disease (retinopathy, neuropathy) are the etiological mechanisms of multisensory impairment. Another possible mechanism is the side effects of anti-DM agents. In conclusion, age-related taste impairment is not uncommon in Japanese men and women and frequently occurs in combination with other sensory impairments. Our results suggest that DM is strongly associated with taste impairment. We would like to acknowledge Hiroe Ide, Noriko Kikuchi, Kenta Endo, Mieko Koike, and Megumu Arai from the Division of Townsperson, Koumi Town Office, Nagano, Japan, for their valuable help. Conflict of Interest: The editor in chief has reviewed the conflict of interest checklist provided by the authors and has determined that the authors have no financial or any other kind of personal conflicts with this paper. Funding Sources: A grant-in-aid from the Ministry of Education, Culture, Sports, Science and Technology, Japan (No. 21390193). Author Contributions: All authors took various roles in study concept, design, data analysis, interpretation of data, and the writing of the letter. Sponsor's Role: The funding agencies had no role in the design or conduct of the study; in the collection, management, analysis, or interpretation of the data; or in the preparation, review, or approval of the manuscript.

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