Taste dysfunction: a practical guide for oral medicine.

Dental practitioners are often the first clinicians to be presented with complaints about changes in taste. This raises a problem in terms of appropriate evaluative response. It is a difficult issue both because of the common confusion between smell and taste problems (with smell being the more vulnerable sense and contributing substantially to the flavor of food that most patients equate with 'taste'), and because of the lack of widely accepted standardized techniques to assess true taste function. This brief review provides a summary of some of the problems associated with assessing taste function in a clinical setting and of patient management options available to the practitioner of oral medicine.

Salty taste acceptance by infants and young children is related to birth weight: longitudinal analysis of infants within the normal birth weight range.

BACKGROUND: Birth weight and sodium intake are both associated with risk for hypertension. It is not known whether birth weight influences response to salty taste. OBJECTIVE: To assess the relationship between birth weight and salty taste acceptance of infants and young children. DESIGN: Acceptance of salty taste was assessed at 2 (n = 80) and 6 (n = 76) months in infants (birth weight >2.5 kg) enrolled in a prospective cohort study. Acceptance was expressed as proportional intake following 1-min ingestion tests with water and salt solutions (0.17 and 0.34 mol/l NaCl, in water). Birth weight was obtained by maternal report. Questionnaires completed by mothers and food-ranking procedures performed by children evaluated salt liking and preference in a subset (n = 38) of subjects at preschool age (36 or 48 months). SETTING: Nonprofit basic research institute in Philadelphia, PA, USA. RESULTS: Regression analysis revealed significant negative associations between birth weight and acceptance of salty taste at 2 months (0.17 mol/l, P < 0.0001; 0.34 mol/l, P < 0.01) but not at 6 months. Relationships were not affected by adjustment for potential confounders. In preschoolers, greater liking of (P < 0.05) and preference for (P < 0.01) salty foods was associated with lower birth weight in simple, but not adjusted, models. CONCLUSION: Measures related to salty taste preference were inversely related to birth weight over the first 4 years of life. Additional studies should substantiate these findings and explore whether early response to salty taste predicts future sodium intake, blood pressure, or other public health-related outcomes. SPONSORSHIP: National Institutes of Health (DC 00882).

The addition of CO2 to traditional taste solutions alters taste quality.

Previous studies of the effect of carbonation on taste perception have suggested that it may be negligible, manifesting primarily in increases in the perceived intensity of weak salt and sour stimuli. Assuming CO2 solutions in the mouth stimulate only trigeminal nerve endings, this result is not altogether surprising; however, there are neurophysiological data indicating that CO2 stimulates gustatory as well as trigeminal fibers. In that case, carbonation might alter the quality profile of a stimulus without producing substantial changes in overall taste intensity--much as occurs when qualitatively different taste stimuli are mixed. To address this possibility, subjects were asked to rate the total taste intensity of moderate concentrations of stimuli representing each of the basic tastes and their binary combinations, with an without added carbonation. They then subdivided total taste intensity into the proportions of sweetness, saltiness, sourness, bitterness and 'other taste qualities' they perceived. The addition of carbonation produced only small increases in ratings of total taste intensity. However, rather dramatic alterations in the quality profiles of stimuli were observed, particularly for sweet and salty tastes. The nature of the interaction is consistent with a direct effect of carbonation/CO2 on the gustatory system, although the possibility that at least some of the observed effects reflect trigeminal-gustatory interactions cannot be ruled out.

Clinical disorders of smell and taste.

Renewed attention to chemosensory dysfunction has revealed that a substantial portion of the population are affected during their lives, many simply as a result of aging. The authors discuss terminology, assessment, etiology, and prognosis and compare current understanding with that presented by Mackenzie in 1884.

Increased liking for salty foods in adolescents exposed during infancy to a chloride-deficient feeding formula.

In a model selected for its similarity to the hormonal consequences of sodium deficiency, food choices of 169 adolescents exposed during infancy to a chloride-deficient feeding formula were compared to those of their closest-aged siblings. Questionnaires completed by parents were used to assess food likes and dislikes. When a salty food was mentioned by parents as one craved by either child, exposed children were more likely than siblings to crave that food (p = 0.005). Frequencies of two of four salt-related dietary behaviors [adding salt to food before tasting (p = 0.03) and to atypical foods (p = 0.05)] were higher in exposed adolescents than in siblings, while frequencies of parallel sugar-related behaviors did not differ between the groups. Foods classified as being lower in saltiness were disliked by exposed children relative to siblings (p = 0.003), although ratings of foods higher in saltiness did not differ. Finally, when asked to rank eight foods in order of preference, ranks assigned by exposed children to salty foods tended (p = 0.07) to be higher than those of siblings. The data suggest a persistent effect of early experience on human salt preference. Additional studies are needed to determine whether salt intake is increased in this and other populations that suffer electrolyte depletion during early development.

Functionally mature olfactory neurons from two anosmic patients with Kallmann syndrome.

Patients with Kallmann syndrome (KS) exhibit hypogonadotropic hypogonadism and anosmia [Kallmann et al., Am. J. Mental Def., 48 (1944) 203-236] secondary to failure of gonadotropin-releasing hormone (GnRH)-producing neurons to migrate from the olfactory placode to the brain, and to agenesis of the olfactory bulbs. It has been hypothesized that olfactory neurons (ON) from individuals with KS are immature partly on the basis of studies in animals showing that lack of synaptic connection of ON with the olfactory bulb results in expression of immature ON [Schwob et al., J. Neurosci., 12 (1979) 880-883]. To test this assumption, we obtained olfactory tissue samples from two males diagnosed with KS on the basis of medical history and MRI studies. Both patients were anosmic. The functioning of cells isolated from biopsies taken from the upper middle turbinate and septum was studied by measuring changes in intracellular Ca2+ concentration ([Cai]) using dual excitation fluorescence microscopy. Biopsies from both patients yielded cells that morphologically appeared to be ON. Seven of 16 cells that morphologically resembled ON responded with a change in [Cai] upon stimulation with an odorant mixture. These studies show that at least some ON in KS individuals are functionally mature and suggest that complete development of the olfactory bulbs is not required for differentiation of mature human ON.

Bitter taste in aging: compound-specific decline in sensitivity.

Threshold sensitivity to and the perceived intensity of two bitter compounds, quinine sulfate and urea, were assessed in 52 young adults and 60 elderly adults. Consistent with previous literature, age-related declines in sensitivity to the bitterness of quinine were observed at both threshold and suprathreshold levels. In contrast, the same young and elderly subjects showed comparable sensitivity to the bitterness of urea. These results provide further support for the existence of multiple bitter taste transduction sequences in humans, and indicate that they may be differentially affected by aging.

Infant salt taste: developmental, methodological, and contextual factors.

Two studies investigated the human infant's response to salt during development. In the first study, measures of intake and sucking were obtained from two groups of infants, newborns and 4- to 8-month-olds, in response to brief presentations of two concentrations of salt (0.2 or 0.4 M) and water. For several measures of sucking and for intake, there were significant age and concentration effects. Generally, newborn infants tended to reject saline relative to water more than did 4- to 8-month-old infants. This result, consistent with previously published research, suggests a developmental change in salt acceptability and, probably, sensitivity in the human infant. In the second longitudinal study, the response to salted (0.15 M) versus unsalted formulas was evaluated monthly in infants 2 to 7 months of age. Again, a developmental change was observed: Based on some sucking measures, younger infants appeared to be indifferent to the salted formula relative to the unsalted formula whereas older infants tended to reject the salted formula, presumably because either it was less sweet than the unsalted formulas or because it was novel. These data are consistent with the hypothesis developed from animal model studies that during early human postnatal development, transductive elements sensitive to saltiness mature.

Dietary assessment of patients with chemosensory disorders.

OBJECTIVE: To identify individuals who are at nutritional risk because of taste and/or smell disorders. DESIGN: Patients referred by a private physician for evaluation of a chemosensory complaint underwent an extensive battery of taste and smell tests, otorhinolaryngologic tests, and, in some cases, periodontal examinations and completed a dietary/health questionnaire, a 24-hour recall, and a 2-day diet record. SETTING: Patients were interviewed at the Monell-Jefferson Chemosensory Clinical Research Center, Philadelphia, Pa. SUBJECTS: We studied 310 patients (142 men and 168 women) with a primary complaint of chemosensory disorder. Mean age was 50.5 +/- 15.7 (range = 15 to 93 years). Normative data were provided by an additional 79 healthy control subjects (42 men and 37 women) with no taste or smell complaint. Their mean age was 48.8 +/- 18.8 years (range = 20 to 83 years). MAIN OUTCOME MEASURES: Chemosensory disorder-related changes in food habits (determined by questionnaire responses), nutrient intake (analysis of 3-day food records), and body weight (self-reported). STATISTICAL ANALYSES: Analysis of covariance, followed by post hoc analysis of adjusted means with the Tukey honestly significant difference test, was used to explore group differences in nutrient intake and body weight. chi 2 Analysis and the Pearson correlation coefficient were used to evaluate relationships between variables. RESULTS: When groups were classified according to chemosensory diagnosis, group differences were observed on global appetitive questions, but complaints were high in all groups. Approximately 65% (203 of 310) of patients had self-reported body weights within 5% of their predisorder weight, but clinically meaningful weight gains or losses were observed in each group. Patients with multiple chemosensory disorders were most likely to lose weight, whereas the incidence of weight gain was highest in patients with anosmia. Patient report of a change in eating patterns was the best predictor of weight change among the variables examined. CONCLUSIONS: Dietary responses to chemosensory disorders vary widely and may place patients at nutritional risk. Until better prognostic indexes are identified, dietitians should query patients about disorder-related alterations in eating patterns and provide appropriate individualized counseling.

Hepatic lipid profiles in miniature pigs after alcohol feeding.

Changes in lipid profiles have not been reported for the known increases in total lipid content in livers of alcoholics. We have reported a lowering of the beta-oxidative capacity of alcoholic livers, and therefore would expect a lower turnover of fatty acids in these livers, and thus a change in lipid profile. The percentage composition of saturated and unsaturated fatty acids in the liver of alcohol-fed miniature pigs versus the controls, as well as the function of distance from the main hepatic vein, have both been determined in this study involving the feeding of ethanol for one year. Livers of alcohol-fed miniature pigs contained more total lipids than those of controls. Results also indicated significantly higher percentages of free fatty acids and triglycerides in the alcohol-fed miniature pigs, and also an increase in percentage total neutral lipids. The effect of distance from the main blood source (and therefore oxygenation) gave a fatty acid profile that showed an increase in the ratio of saturated to unsaturated fatty acids with increasing distance from the right hepatic vein. This change in ratio was independent of alcohol feeding.

Hyposmia in allergic rhinitis.

BACKGROUND: The association between nasal allergy and loss or diminution of smell is frequently alluded to in the literature; however, neither the true prevalence of hyposmia in individuals with allergic rhinitis nor its bases have been established. METHODS: We assessed olfactory threshold for phenylethyl alcohol in 91 patients with symptoms of allergic rhinitis and 80 nonatopic control subjects. To determine the degree to which nasal congestion contributes to hyposmia in allergic rhinitis, total nasal resistance was measured in 64 of the patients and 72 of the control subjects. RESULTS: Olfactory thresholds were significantly higher in allergic patients than in control subjects (p < 0.001), with 23.1% of the patients demonstrating a clinically significant smell loss (defined as threshold at or above the 2.5th percentile of control values). Although nasal resistance was significantly higher among patients than among controls (p < 0.001), it was not related to olfactory threshold in either group. Clinical or radiographic evidence of sinusitis or nasal polyps or both in allergy patients was found to be significantly associated with hyposmia (p < 0.006). CONCLUSIONS: The observed prevalence of hyposmia among patients with allergic rhinitis suggests that this is a major etiologic factor contributing to smell disorders. Sinusitis or nasal polyps or both may underlie many cases of allergy-related hyposmia.

Non-oral etiologies of oral malodor and altered chemosensation.

A number of non-oral causes for oral malodor have been discussed. Several well documented etiologies for non-oral malodor include renal failure, cirrhosis of the liver, and diabetes mellitus. Each of these conditions has been examined using analytical instrumentation. In addition there appear to be several other metabolic conditions involving enzymatic and transport anomalies (such as trimethylaminuria) which lead to the systemic production of volatile malodors that manifest themselves as halitosis and/or altered chemoreception. Our studies include patients who have been referred to us after being examined by numerous clinical specialists with no identification or relief from their problem. This is due in part to the intermittent nature of many of these problems as well as an apparent lack of knowledge concerning many of these metabolic problems and their relation to oral symptoms.

Early developmental change in bitter taste responses in human infants.

Human newborns (birth-6 days) and older infants (14-180 days) were allowed to ingest both urea (0.12-0.24 M) in a mildly sweet diluent and the diluent alone, and multiple measures of responsivity were obtained (relative intake, sucking behavior, and hedonic ratings based on facial expressions and body movements). For newborns, there was no indication of rejection of urea relative to the diluent in measures of intake or sucking behavior; rather, their responses were predominantly controlled by the order of presentation of the two tastes. In contrast, older infants tended to reject all concentrations of urea according to these measures. Hedonic ratings provided an indication of limited rejection of the bitter taste by newborns, but older infants were still found to respond more consistently. These data suggest there is an early developmental change in bitter taste perception.

Dietary evaluation of patients with smell and/or taste disorders.

The impact of smell and taste disorders on dietary habits and nutritional status has received limited research attention. This paper reports findings obtained from questionnaires and diet records completed by 40 healthy subjects and 118 patients with chemosensory dysfunction. Chemosensory disorders were frequently associated with decreases in food acceptability. Although dietary responses to these dysfunctions varied greatly, patients with distorted or phantom smell and/or taste sensations tended to report weight loss whereas those with simple sensory loss were more likely to report weight gain. Indices derived from diet records did not indicate that either group of patients was at substantial nutritional risk, but food frequency responses and estimates of body mass index were consistent with patient reports of changes in dietary patterns and weight. In addition, marked weight change and aberrant dietary practices were noted in individual patients. Thus, there were indications that chemosensory dysfunction may be associated with nutritionally important dietary alterations.

The importance of sensory context in young children's acceptance of salty tastes.

Acceptance of and expressed preference for varying levels of salt (NaCl) were assessed among children 3-6 years of age. 20 children received 0, 0.17, and 0.34 M NaCl in aqueous solution, and 20 received these same NaCl concentrations in a soup broth. In both groups, children were asked to ingest as much as they wanted to each stimulus during brief, sequential presentations and to indicate which stimulus they preferred in a series of paired-comparison presentations. A striking, context-specific reaction to the taste of salt was observed on both measures. Children in this age group strongly rejected even the moderate level of salt in water relative to unsalted water. In contrast, the most highly salted soup was well accepted and preferred to either unsalted or moderately salted soup by the majority of children.

Taste intensity perception in aging.

Men (n = 91) and women (n = 79) between the ages of 23 and 88 years made cross-modal matches of distance to the perceived intensity of aqueous solutions representing the four basic taste qualities. Traditional analysis, which characterizes age-group performance in terms of the slope of a group's psychophysical function, yielded results consistent with previous findings in that some flattening of slope was observed in the oldest group. Analyses based on the slope of the functions generated by individual participants demonstrated significant regression on age for some qualities. None of these findings were observed in the analogous analysis of variance (ANOVA). Significant age-related changes in Intraclass Correlation Coefficient (ICC) were demonstrated by both ANOVA and regression analysis. The ICC reflects the consistency of an individual's discriminative response over repeated stimulus presentations. Its variation with age was dependent upon taste quality.

Developmental changes in salt acceptability in human infants.

Human infants less than 4 months of age ingested water and moderate concentrations of sodium chloride solution (0.10-0.20 M) in equal amounts. In contrast, infants 4-24 months of age exhibited heightened acceptance of saline solution relative to water. Such a developmental change in salt acceptability is consistent with a hypothesis of postnatal maturation of peripheral and/or central structures underlying this response. Children 31-60 months of age tended to reject saline solution relative to water. This change may in part reflect the effects of experience.

Congenital and experiential factors in the development of human flavor preferences.

Experimental modifications of congenitally based human responses to taste stimuli are being evaluated during the first few years of life. Sweet- and salty-tasting substances form the focus of our research. Prior studies indicate that human preference for sweet substances is innate whereas need-free acceptance of salty-tasting substances has been thought to be learned. Our recent studies indicate that ingestive expression of the innate preference for sweet tasting substances may be subject to modification quite early in life, although the effects of experiences are specific to the particular food context in which sweet is experienced. A sense of what should and should not be sweet, rather than a generalized hedonic responsiveness to sweetness itself, appears to be shaped through dietary experience. In studies with salt (NaCl), our data reveal two distinct changes in the acceptance of near-isotonic salt solutions during early development. The first is a shift from indifference to relative (to water) preference which appears around 4 months of age. We hypothesize this is due to maturation rather than learning. The second shift is one from relative acceptance to relative rejection which is variable in its time of appearance (although it occurs by 2 to 3 years of age in populations we have studied) and is probably due in part to the development of neophobia in conjunction with a lack of experience with salty water. We suggest that in the absence of need, the appeal of both sweet- and salty-tasting substances, in large part at least, is innately determined. Dietary experience during development determines the appropriate food-related contexts for these appealing tastes.