Journal of Health Care and Research
Article Type: Original Article
J Health Care and Research. 2023 Aug 21;4(3):81-88
Comparison of The Salty Taste Test Results, The Olfactory Test Results, and Questionnaire Survey Results before the COVID-19 Epidemic (2019) and after the COVID-19 Epidemic (2022) in The Medical Examination for Residents of Yakumo Town, Hokkaido, Japan in the Same 100 Participants
Corresponding Author: Naomi Katayama
Address: Nagoya Women’s University, Department of Health Science, Japan.
Received date: 03 August 2023; Accepted date: 14 August 2023; Published date: 21 August 2023
Citation: Katayama N. Comparison of The Salty Taste Test Results, The Olfactory Test Results, and Questionnaire Survey Results before the COVID-19 Epidemic (2019) and after the COVID-19 Epidemic (2022) in The Medical Examination for Residents of Yakumo Town, Hokkaido, Japan in the Same 100 Participants. J Health Care and Research. 2023 Aug 21;4(3):81-88.
Copyright © 2023 Katayama N. This is an open-access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium provided the original work is properly cited.
Keywords: Yakumo Study, Taste Test, Olfactory Test, Questionnaire Survey, COVID-19
Since 2005, we have conducted a questionnaire survey on taste and olfaction, the salty taste test, and the olfactory test in Yakumo Town, Hokkaido, Japan. However, due to the COVID-19 epidemic, resident screening was canceled in 2020 and 2021. We investigated the potential impact of COVID-19 by comparing results from the salty taste test, olfactory tests, and questionnaire surveys. Data were analyzed for a total of 100 individuals, 42 males, and 58 females, who underwent screening in both 2019 and 2022. The questionnaire survey included items regarding the subjective presence or absence of dizziness, tinnitus, headache, taste, smell, and saliva secretion.
Furthermore, we obtained results from a salty taste test using the Solsave kit (manufactured by Advantech) and olfactory test results using the smell stick kit (manufactured by Daiichi Kogyo Co., Ltd.). Consequently, when comparing the results of the olfactory test between 2019 and 2022 for 42 males, a statistically significant difference (p = 0.004) emerged. The ability to understand odors was more challenging in 2022 compared to 2019. Specifically, distinguishing between the odors of perfume (p = 0.044), menthol (p = 0.032), mandarin orange (p = 0.032), and fried garlic (p = 0.019) proved to be difficult.
Similarly, in the comparison of 2019 and 2022 for 58 females, there was a statistically significant difference (p = 0.033) in olfactory test results, indicating that comprehending odors was more difficult in 2022 than in 2019. Particularly, distinguishing between the odors of perfume (p = 0.026), mandarin orange (p = 0.026), and condensed milk (p = 0.018) presented challenges. There was no statistically significant difference in the results of the salty taste test and questionnaire survey for both males and females. To determine whether the observed changes in olfactory sense are due to aging changes over the three years or the effects of COVID-19, ongoing investigation is crucial. It is necessary to continue assessing whether this diminished sense of smell will recover in the future.
Since 2005, we have continued to conduct surveys using questionnaires, the salty taste test kit, and the olfactory test kit at the Yakumo Town residents’ medical examination in Hokkaido, Japan. We have previously reported that the sensitivity threshold for salty taste is preserved with age, but that the sense of smell declines with age [1-5]. We also reported that men’s sense of smell declines faster than women’s [1-5]. Other researchers have reported a decline in the sense of smell and taste as an early symptom of Alzheimer’s dementia . Additionally, other researchers have reported that having COVID-19 affects one’s sense of smell and taste [7-16]. This time, we decided to compare the data of the same participants in the health checkup for residents of Yakumo Town, Hokkaido, Japan, which we have been conducting for many years, to examine whether the sense of taste and smell changed before and after the COVID-19 epidemic.
Material and Method
Using the salty taste test kit (Solsave: manufactured by Advantech Co., Ltd.), the taste was measured by holding filter paper impregnated with 0.6%, 0.8%, 1.0%, 1.2%, 1.4%, and 1.6% salty taste in the mouth and feeling the salty taste. % was recorded as the result.
Using the olfactory test kit (smell stick: Daiichi Kogyo Co., Ltd.), 12 types of olfaction (ink, lumber, perfume, menthol, mandarin orange, curry, household gas, rose, cypress, stuffy socks, sweat, etc.) were tested. (smell of milk, condensed milk, sautéed garlic) was rubbed with a finger on an oiled filter paper, each of which was confined in minute capsules.
The questionnaire survey included self-reported responses regarding subjective dizziness (1. Never, 2. Occasionally, 3. Often) and subjective tinnitus (1. Never, 2. Occasionally, 3. Always). Participants were also asked about the subjective presence or absence of headaches (1. No, 2. Yes) and their subjective sense of smell (1. Not at all, 2. Slightly, 3. Sometimes difficult to understand, 4. Good). Furthermore, subjects were requested to indicate the status of their sense of taste (1. Not at all, 2. Slightly, 3. Sometimes difficult to understand, 4. Understandable) and the subjective level of saliva secretion (1. Often, 2. Normal, 3. Slightly). Refer to Table-1 for details.
Table-1: Subjective Questionnaire Survey Results and Answer Options
The results were processed statistically. An F-test was conducted to compare 2019 and 2022 for males and females, respectively. In cases where no significant difference was found in the F-test, the paired Student’s t-test was employed. Conversely, when a significant difference was observed, the Wilcoxon test was used to confirm the presence or absence of statistical significance. Additionally, concerning the gender difference between 2019 and 2022, following the F-test, the unpaired Student’s t-test was utilized if no significant difference was present. Alternatively, if a significant difference existed, the Mann-Whitney test was employed to perform the statistical analysis. The presence or absence of a significant difference was ascertained.
Out of the 100 participants, 42 were male, and 58 were female. The age distribution is displayed in Table-2.1 for 2019 and Table-2.2 for 2022. The majority of the participants were in their 60s, followed by individuals in their 70s.
Table-2.1: Age Distribution of 100 People who Participated in the Yakumo Residents’ Medical Examination in 2019
Table-2.2: Age Distribution of 100 People who Participated in the Yakumo Residents’ Medical Examination in 2022
The questionnaire survey results for males are presented in Table-3.1, while the results for females are shown in Table-3.2. The salty taste test results for males can be found in Table-4.1, and for females, they are presented in Table-4.2. Additionally, the olfactory test results for males are displayed in Table-5.1, and for females, they are shown in Table-5.2 below.
Table-3.1: Subjective Questionnaire Survey Results (2019 and 2022) Males (n=42)
Table-3.2: Subjective Questionnaire Survey Results (2019 and 2022) Females (n=58)
Table-4.1: Comparison of the Saltiness Test Results (2019 and 2022) Males (n=42)
Table-4.2: Comparison of the Saltiness Test Results (2019 and 2022), Females (n=58)
Table-5.1: Comparison of the Number of Correct Answers in the Odor Test (2019 and 2022) Males (n=42)
Table-5.2: Comparison of the Number of Correct Answers in the Odor Test (2019 and 2022) Females (n=58)
In the results of the self-administered questionnaire survey, a statistical comparison was conducted between 2019 and 2022 (Male: Table-6.1, Female: Table-6.2). There was no significant difference observed for subjective dizziness, tinnitus, headache, taste, olfactory perception, and saliva secretion.
Table-6.1: Comparison of Questionnaire Survey Results of 42 Male in 2029 and 2022
Table-6.2: Comparison of Questionnaire Survey of Questionnaire Survey Results of 58 Females in 2029 and 2022
There were no significant differences in the results of the salty taste test (refer to Table-7). However, the olfactory test results exhibited a statistically significant disparity. Both males (p = 0.004) and females (p = 0.033) displayed notably less distinguishable olfactory test outcomes in 2022 as compared to 2019. It was observed that males had a higher level of obscurity compared to females.
Table-7: Comparison Results of 42 Males and 58 Females in 2029 and 2022
Based on the aforementioned outcomes, the count of accurate responses for each odor in 2019 and 2022 is provided (male: Table-8.1, female: Table-8.2). The tally of correct answers for each odor in the olfactory test results was subjected to statistical comparison using the chi-square test (refer to Table-9).
Table-8.1: Comparison of the Percentage of Correct Answers in the Odor Test (2019 and 2022) Males (n=42)
Table-8.2: Comparison of the Percentage of Correct Answers in the Odor Test (2019 and 2022) Females (n=58)
Table-9: Comparison of Correct and Incorrect Answers for each Odor in Olfactory Test Results (Chi-Square Test)
Consequently, out of the 12 odor types, males exhibited a notable decline in the perception of perfume (p = 0.044), menthol (p = 0.032), mandarin orange (p = 0.032), and fried garlic (p = 0.019), with these odors being significantly less distinguishable in 2022 compared to 2019.
Among the 12 odors, females demonstrated an increased difficulty in discerning the scents of perfume (p = 0.026), mandarin orange (p = 0.026), and condensed milk (p = 0.018) in 2022 compared to 2019. Statistically, the ability to detect these smells became more challenging with age.
Furthermore, a statistical comparison was conducted between male and female odor test results for the same year. As a result, a significant difference between males and females was observed in 2019 for India ink (p = 0.024), indicating that males had more difficulty in perceiving the smell compared to females.
In addition, the odor that showed a statistically significant difference between male and female in 2022 was rose (p = 0.036), and it was difficult for male to understand the odor compared to female.
In this study, we conducted a comparison of taste test results, olfactory test results, and questionnaire survey responses for the same participants before and after the COVID-19 epidemic, during annual health checkups for residents in Yakumo, Hokkaido, Japan, where population movement is limited. We examined post-2019 (pre-COVID-19 epidemic) and 2022 (post-COVID-19 epidemic) outcomes for subjective dizziness, tinnitus, headache, taste, smell, and salivation among 42 males and 58 females. The results were compared, and no statistical significance was observed for any of the mentioned items.
We also compared post-2019 (pre-COVID-19 epidemic) and 2022 (post-COVID-19 epidemic) taste test and olfactory test results among 42 males and 58 females. The taste test results did not show any statistically significant difference. However, the olfactory test results exhibited a reduction in 2022 compared to 2019, with a statistically significant decrease in the number of recognizable odors.
Past research has indicated that males perform less well on olfactory tests compared to females [1-5], and there is a statistically significant decline in olfactory perception with advancing age [1-5]. We have previously reported that taste test results remain consistent across different ages for both males and females. Recent reports have highlighted cases demonstrating anomalies in the sense of taste and smell due to the COVID-19 epidemic [7-16].
It remains unclear whether the observed decline in the sense of smell, as revealed in this study, is primarily a result of the aging process over the three-year period or if it has been influenced to a significant extent by the COVID-19 epidemic. Further follow-up involving an additional 100 participants will be essential to gain deeper insights in the future.
Taste and smell test results, along with questionnaire survey responses, were compared in the same participants before and after the COVID-19 epidemic (2019 and 2022: 42 males and 58 females). The findings revealed that there was no statistically significant difference in the taste test results. However, the olfactory test results indicated a lower value in 2022 compared to 2019, accompanied by a reduced ability to recognize odors. Nonetheless, this study does not conclusively determine whether the decline in the sense of smell is attributed to the natural aging process over the three-year period or if it is influenced by the impact of the COVID-19 epidemic. To gain more insights, further follow-up investigations are necessary in the future.
The studies involving human participants were reviewed and approved by the Ethics Committee of Nagoya University School of Medicine (approval number 2014–0207). The participants provided their written informed consent to participate in this study.
This study was supported by the Ministry of Education, Culture, Sports, Science and Technology Grand-in-Aid for Scientific Research JP20K02372.
Conflict of Interest
The author has read and approved the final version of the manuscript. The author has no conflicts of interest to declare.
 Katayama N, Kondo S, Suzuki S, Ishiguro S, Kondo N, Amano N, Okuda K. Results of the Olfactory Cognition Test Performed on 117 Peoples. Global Journal of Medical Research. 2020;20(6):19-21.
 Katayama N, Kondo S, Ando Y, Ashihara Y, Kawano N, Shibuya M, Nanao M, Mase I, Abe M, Kouno M, Narimoto Y. Results of Comparison of Two Types of Olfactory Recognition Tests Performed on 112 Peoples. -34 High School Students, 55 University Students, and 23 Middle-Aged. Global Journal of Medical Research, 2020;20(6):31-35.
 Katayama N, Kondo S, Sugimoto S, Kinoshita W, Teranishi M, Sone M, Fujimoto Y, Otake H, Suzuki H, Sugiura S, Nakada T, Saji N, Nakata S, Nakashima T. Odour and salt taste identification in older adults: Evidence from the Yakumo Study in August, 2018. Acad. J. Med. Plants. 2018 Mar 13;7(3):66-71.
 Katayama N, Kondo S, Sugimoto S, Yoshida T, Teranishi M, Sone M, Fujimoto Y, Otake H, Suzuki H, Nakada T, Saji N, Nakata S, Nakashima T. Odour and salt taste identification in older adults: Evidence from the Yakumo. Academia Journal of Medicinal Plant. 2019;8(3):30-35.
 Naomi Katayama, Shoko Kondo. Comparison of Subjective Feeling of Dizziness and Simple Taste/Olfactory Test Results in Elderly People (Over 60 Years Old). Global Journal of Medical Research. 2020;22(2):1-8.
 Özçelik Korkmaz M, Eğilmez OK, Özçelik MA, Güven M. Otolaryngological manifestations of hospitalised patients with confirmed COVID-19 infection. Eur Arch Otorhinolaryngol. 2021 May;278(5):1675-85. [PMID: 33011957]
 Thrane JF, Britze A, Fjaeldstad AW. Incidence and duration of self-reported hearing loss and tinnitus in a cohort of COVID-19 patients with sudden chemosensory loss: A STROBE observational study. Eur Ann Otorhinolaryngol Head Neck Dis. 2022 May;139(3):125-28. [PMID: 34602376]
 Espinoza-Valdez A, Celis-Aguilar E, Torres-Gerardo F, Cantú-Cavazos N, Dehesa-Lopez E. In Search of a Neurotologic Profile in COVID-19 – A Study in Health Care Workers. Cureus. 2022 Jan 7;14(1):e21015. [PMID: 35028241]
 Daher GS, Nassiri AM, Vanichkachorn G, Carlson ML, Neff BA, Driscoll CLW. New onset tinnitus in the absence of hearing changes following COVID-19 infection. Am J Otolaryngol. 2022 Jan-Feb;43(1):103208. [PMID: 34536917]
 Favero R, Hajrulla S, Bordin A, Mucignat-Caretta C, Gaudioso P, Scarpa B, Favero L, Ottaviano G. Olfactory Dysfunction in COVID-19 Patients Who Do Not Report Olfactory Symptoms: A Pilot Study with Some Suggestions for Dentists. Int J Environ Res Public Health. 2022 Jan 18;19(3):1036. [PMID: 35162061]
 Beukes EW, Baguley DM, Jacquemin L, Lourenco MPCG, Allen PM, Onozuka J, Stockdale D, Kaldo V, Andersson G, Manchaiah V. Changes in Tinnitus Experiences During the COVID-19 Pandemic. Front Public Health. 2020 Nov 5;8:592878. [PMID: 33251179]
 Boscolo-Rizzo P, Hummel T, Hopkins C, Dibattista M, Menini A, Spinato G, Fabbris C, Emanuelli E, D’Alessandro A, Marzolino R, Zanelli E, Cancellieri E, Cargnelutti K, Fadda S, Borsetto D, Vaira LA, Gardenal N, Polesel J, Tirelli G. High prevalence of long-term olfactory, gustatory, and chemesthesis dysfunction in post-COVID-19 patients: a matched case-control study with one-year follow-up using a comprehensive psychophysical evaluation. Rhinology. 2021 Dec 1;59(6):517-27. [PMID: 34553706]
 Nakashima T, Suzuki H, Teranishi M. Olfactory and gustatory dysfunction caused by SARS-CoV-2: Comparison with cases of infection with influenza and other viruses. Infect Control Hosp Epidemiol. 2021 Jan;42(1):113-14. [PMID: 32366336]
 Park DY, Kim HJ, Kim CH, Lee JY, Han K, Choi JH. Prevalence and relationship of olfactory dysfunction and tinnitus among middle- and old-aged population in Korea. PLoS One. 2018 Oct 23;13(10):e0206328. [PMID: 30352085]