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Source: Compiled from fact sheets produced by the National Institute on Deafness and Other Communication Disorders (NIDCD).
Approximately 25 percent of Americans are nontasters, 50 percent are medium tasters, and 25 percent are "supertasters."
More than 200,000 people visit a physician for chemosensory problems such as taste disorders each year. Many more taste disorders go unreported.
Some people are surprised to learn that flavors are recognized mainly through the sense of smell. If you hold your nose while eating chocolate, for example, you will have trouble identifying the chocolate flavor—even though you can distinguish the food's sweetness or bitterness. That is because the distinguishing characteristic of chocolate (what differentiates it from caramel, for example) is sensed largely by its odor.
Taste cells (along with smell cells) are the only sensory cells that are regularly replaced throughout a person's life span. Taste cells usually last about 10 days.
Taste buds, located mainly on the lingual surface, palate, and oropharynx, are primarily responsible for mediating sweet, sour, bitter, salty, and metallic sensations. The physiologic role of the taste system is multifold and includes (a) triggering ingestive and digestive reflex systems that alter the secretion of oral, gastric, pancreatic, and intestinal juices (Schiffman, 1997; Giduck et al., 1987), (b) reinforcing the ingestive process by enhancing the feelings of pleasure and satiety (Warwick et al., 1993), and (c) enabling the determination of the quality of sampled foodstuffs and distinguishing nutrients (which usually taste "good", e.g., sweet) from potential toxins (which usually taste "bad", e.g., bitter)(McLaughlin and Margolskee, 1994). Although rarely appreciated, taste dysfunction can alter food choices and patterns of consumption, producing weight loss, malnutrition, and in some cases impaired immunity and even death. Apparent increased sensitivity and aversion to bitter-tasting substances on the part of the pregnant mother during the first trimester presumably reflects the need to detect and avoid bitter tasting poisons and teratogens during this critical phase of fetal development (Duffy et al., 1998). Similarly, increased preferences for salty and bitter tasting substances during the remainder of pregnancy likely encourages the eating of a varied diet and the ingestion of much needed electrolytes to expand fluid volume. In someone who is hypertensive or diabetic, taste loss can lead to a dangerous tendency to over-compensate for the loss by adding additional salt or sugar to the food.
Whole mouth taste dysfunction is rare, largely because of the redundant innervation of the taste buds (some buds are innervated by CN VII, some by CN IX, and some by CN X). Nonetheless, such function decreases with aging to some degree, can be influenced by central tumors and lesions (e.g., ischemic infarcts secondary to stroke), and is altered adversely by a number of medications. Regional taste deficits, which are much more common, often go undetected, reflecting, in part, the aforementioned redundant neural innervation. Regional deficits can be quite marked. For example, in one study none of 12 elderly persons detected NaCl presented to small regions of the tongue, unlike 12 younger individuals who exhibited no problems with such detection (Matsuda & Doty, 1995). Importantly, taste sensitivity, as measured by detection thresholds, is directly related to the number of taste papillae and taste buds stimulated, implying that some taste disorders are conceivably accounted for by changes in the peripheral lingual anatomy (Doty et al., 2001; Miller et al., 2002).
The most debilitating taste disorders are those in which a persistent, often chronic, bad taste is present, such as a bitter or salty taste. The causes of such dysgeusias are poorly understood, although they usually appear later in life. In additional to dental and oral health considerations (e.g., the presence of dissimilar metals in oral appliances, purulent discharge from infected teeth or gums), viruses, physical damage to one or more taste nerves, and various medicines are a cause of some dysgeusias. Among offending medicines are lipid reducing agents, antibiotics, and antihypertensive, anxiolytic, and antidepressant drugs. Fortunately, most dysgeusias spontaneously resolve over time (Deems et al., 1996).
Formal determinations of the prevalence of taste dysfunction in the general population are not available, although a large literature exists on differential sensitivity to bitter tasting agents, such as phenothiocarbamide (PTC) and 6-n-propylthiouracil (PROP). Variations in sensitivity seem to vary among genetically disparate populations, although the methods of determining such differential sensitivity are varied. Based upon suprathreshold scaling, some investigators have divided individuals into nontasters, medium tasters, and supertasters. In the case of PROP, Bartoshuk et al. (1998) estimate that approximately 25% of Americans are nontasters, 50%, medium tasters, and 25%, supertasters. Such tasting ability correlates with the number of fungiform papillae, as well as sensitivity to some other agents (e.g., NaCl, sucrose), begging the question as to whether sensitivity to PROP is a simple reflection of the number of taste buds. However, the relationship between such a classification scheme and clinical pathology, if any, has not been elucidated. Interestingly, PTC sensitivity is reportedly higher in some patient populations (e.g., tuberculosis), suggesting a linkage with susceptibility to some diseases (Freire-Maia & Quelce-Salgado, 1997).
Taste problems are much less prevalent than olfactory ones. In patients presenting to taste and smell centers with chemosensory dysfunction, the vast majority exhibit no taste demonstrable dysfunction at all (Deems et al., 1991; Goodspeed et al., 1986), even though most exhibit bilateral deficits in olfactory functioning. However, most such studies have employed whole-mouth taste tests.
Bartoshuk, L.M., Duffy, V.B., Lucchina, L.A., Prutkin, J., and Fast, K. PROP (6-n-propylthiouracil) supertasters and the saltiness of NaCl. Annals of the New York Academy of Sciences. 855:793-796, 1998.
Deems, D.A., Doty, R.L., Settle, R.G., Moore-Gillon, V., Shaman, P., Mester, A.F., Kimmelman, C.P. Brightman, V.J. & Snow, J.B., Jr. Smell and taste disorders: A study of 750 patients from the University of Pennsylvania Smell and Taste Center (1981-1986). Archives of Otolaryngology -- Head and Neck Surgery 117:519-528, 1991.
Deems, D.A., Yen, D.M., Kreshak, A. & Doty, R.L. Spontaneous resolution of dysgeusia. Archives of Otolaryngology -- Head and Neck Surgery 122: 961-963, 1996.
Doty, R.L., Bagla, R., Morgenson, M. & Mirza, N. NaCl thresholds: Relationship to anterior tongue locus, area of stimulation, and number of fungiform papillae. Physiology & Behavior 72: 373-378, 2001.
Duffy, V.B., Bartoshuk, L.M., Striegel-Moore, R. and Rodin, J. Taste changes across pregnancy. Annals of the New York Academy of Sciences 855:805-809, 1998.
Freire-Maia, A. & Quelce-Salgado, A. Taste sensitivity to P.T.C. in samples from three Brazilian populations. Annals of Human Genetics 24:-102, 1997.
Giduck, S.A., Threatte, R.M. & Kare, M.R. Cephalic reflexes: their role in digestion and possible roles in absorption and metabolism. Journal of Nutrition 117:1191-1196, 1987.
Goodspeed, R.B., Gent, J.F. & Catalanotto, F.A. Chemosensory dysfunction: clinical evaluation results from a taste and smell clinic. Postgraduate Medicine 81-251-260, 1987.
Matsuda, T. & Doty, R.L. Age-related taste sensitivity to NaCl: Relationship to tongue locus and stimulation area. Chemical Senses 20: 283-290, 1995.
*McLaughlin, S. & Margolskee, R.F. The sense of taste. American Scientist 82:538-545, 1994
Miller, S.L., Mirza, N. & Doty, R.L. Electrogustometric thresholds: Relationship to anterior tongue locus, area of stimulation, and number of fungiform papillae. Physiology & Behavior 75: 753-757, 2002.
*Schiffman, S.S. Taste and smell losses in normal aging and disease. Journal of the American Medical Association 278:1357-1362, 1997
*Schiffman, S.S. & Gatlin, C.A. Clinical physiology of taste and smell. Annual Review of Nutrition 13: 405-436, 1993.
Warwick, Z.S., Hall, W.G., Pappas, T.N. & Schiffman, S.S. Taste and smell sensations enhance the satiating effect of both a high-carbohydrate and a high-fat meal in humans. Physiology & Behavior 53:553-563, 1993
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Alzheimer's Disease - alzheimer's disease[mh] & (ep[sh] OR incidence[mh] OR prevalence[mh])& ( communications disorders [mh] OR deafness[mh] OR "hearing impairment" OR "hearing disorders"[mh] OR "sensation disorders"[mh]) - limits Publication Date from 1997, English ; alzheimer's disease[mh] & (ep[sh] OR incidence[mh] OR prevalence[mh])& ( communications disorders [mh] OR deafness[mh] OR "hearing impairment" OR "hearing disorders"[mh] OR "sensation disorders"[mh]) - limits Publication Date from 1992, English, Reviews
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