The important role of umami taste in oral and overall health
© Sasano et al.; licensee BioMed Central. 2015
Received: 2 December 2014
Accepted: 2 December 2014
Published: 26 January 2015
There is a close relationship between an individual’s perception of umami taste and that individual’s physical condition. Our newly developed umami taste sensitivity test revealed the loss of only the umami taste sensation with preservation of the other four basic taste sensations (sweet, salty, sour, and bitter) in some elderly patients. All such patients complained of appetite and weight loss, resulting in poor overall health. We also found that treatment of hyposalivation diminishes hypogeusia, indicating that salivation is essential to the maintenance of normal taste function. Based on these findings, we consider that improvement in salivary flow may serve as a treatment for patients with taste disorders. Umami taste stimulation increases the salivary flow rate because of the gustatory–salivary reflex. We used Japanese Kobucha (kelp tea: tea made of powdered tangle seaweed) to stimulate umami taste and promote reflexive salivation. Improvements were noted in salivation, taste function, appetite, weight, and overall health. Maintenance of umami taste function contributes not only to the preservation of good oral health but also to the general overall health in elderly people.
KeywordsUmami Taste disorder Dry mouth Gustatory–salivary reflex Overall health
Enjoyment of taste should be one of the greatest pleasures in human life. However, aging is sometimes associated with decreased taste sensitivity. Loss of adequate gustatory function may induce a poor appetite, reduced dietary intake, and weight loss, particularly in the elderly . In Japan, gustatory function is generally assessed using the filter paper disk test, in which a filter paper soaked with a taste-inducing chemical solution is placed on specific areas of the tongue and oral cavity. However, this test only assesses four of the five basic tastes: sweet, salty, sour, and bitter. Because the taste quality of umami, which is recognized as a fifth taste category [2–4], is not clinically assessed at present, information about umami taste disorders has yet to be accumulated. We recently reported the specific loss of the umami taste sensation with preservation of the other four taste sensations in some elderly patients [5, 6]. The patients with loss of umami taste sensation also exhibited poor general health. In this article, we first review our studies, including that of our newly developed umami taste sensitivity test, and related studies concerning taste disorders with particular focus on umami taste disorders and overall health. Second, we examine the link between taste disorders and salivary flow because saliva assists and influences the detection of taste by allowing diffusion of the taste substances to the taste receptors, facilitating chemical interactions with food substances, and protecting the taste buds . Finally, we discuss clinical application of taste stimulation as a remedy for dry mouth-related dysgeusia based on the gustatory–salivary reflex.
Importance of umami taste sensation in the elderly
In our taste clinics, we sometimes meet elderly patients with taste disorders who complain of persistent impaired umami taste, although the other four basic taste sensations are normal. Because of the loss of umami taste, these patients experience appetite and weight loss, resulting in poor overall health. Unfortunately, the currently available clinical examinations result in a diagnosis of normal taste sensation in such patients with impaired umami taste because they have normal thresholds for the other four taste qualities. Umami taste receptors reportedly exist not only in the oral tissues but also in the gut. T1R receptors, which mediate umami taste, are expressed on cells of both the duodenum [8, 9] and tongue, suggesting that the umami taste sensation functions in nutrient sensation and digestion in the gut . This evidence indicates that the ability to detect umami flavors is very important for maintaining a healthy daily life. This is particularly true for the elderly because physiological functions and basic physical conditions decline with aging. Therefore, it is important that we are able to assess and treat umami taste impairment. At present, however, there is no clinical method with which to assess umami taste sensitivity.
Development of umami taste sensitivity test
Diagnostic performance of umami taste sensitivity test for assessment of umami taste disorder
200 mM MSG
50 mM MSG
50 mM MSG
Diagnostic accuracy (TP + TN)
Clinical significance of umami taste perception
We assessed 44 patients who visited our clinic with a subjective feeling of dysgeusia using the new umami taste sensitivity test described above. We found that 16% of the patients showed a higher RT only for the umami taste; the RTs for the other four basic tastes were all within the normal range. All patients with an umami-specific taste disorder were >65 years of age, and all complained of appetite and weight loss with resultant poor overall health. Interestingly, the chief complaints of most of these patients were that food was not palatable and that they did not eat normally because of appetite loss . Because all of these patients were elderly, one of the contributors to the development of umami taste dysfunction might be aging. Additionally, most of the patients with loss of umami taste also had systemic diseases (such as diabetes, gastric diseases, and/or depression) and/or oral diseases (such as oral stomatitis, oral candidiasis, and/or oral dryness) and were taking medications. Many of these diseases and medications are known to have side effects of taste disorders or hyposalivation, as described in the next section. After improvement of the patients’ umami taste sensitivity, the patients also experienced remarkable improvements in their appetite and weight because food regained its palatability. All were pleased with the improvement in their health [6, 11]. These results indicate that the umami taste sensation is very important to the maintenance of good health in the elderly.
Link between taste disorders and salivary flow
Remedy for dry mouth-related hypogeusia based on the gustatory-salivary reflex
Taste dysfunction has a negative effect on health. In particular, loss of umami taste causes deterioration in overall health because of appetite and weight loss. Taste function and salivation are closely related to each other. The sense of umami taste promotes salivary secretion, and saliva strongly influences oral functions such as taste sensation. Thus, umami taste function seems to play an important role in the maintenance of oral and overall health.
The present study was conducted according to the guidelines in the Declaration of Helsinki (http://www.wma.net) and was approved by a local ethics committee (the Ethics Committee of Tohoku University Graduate School of Dentistry, approved Nos. 22–21 and 23–23). Written informed consent was obtained from all participants.
stimulated salivary flow
minor salivary gland flow.
This work was supported in part by grants-in-aid (Nos. 22590575, 24659931, 24590780, and 25305039) from Japan Society for the Promotion of Science (JSPS). The funders had no role in the study design, data collection and analysis, decision to publish, or preparation of the manuscript.
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