Search

Anosmia and hyposmia, the inability or decreased ability to smell, is estimated to afflict 3-20% of the population. Risk of olfactory dysfunction increases with old age and may also result from chronic sinonasal diseases, severe head trauma, and upper respiratory infections, or neurodegenerative diseases. These disorders impair the ability to sense warning odors in foods and the environment, as well as hinder the quality of life related to social interactions, eating, and feelings of well-being. This article reports and extends on a clinical update commencing at the 2016 Association for Chemoreception Sciences annual meeting. Included were reports from: a patient perspective on losing the sense of smell with information on Fifth Sense, a nonprofit advocacy organization for patients with olfactory disorders; an otolaryngologist's review of clinical evaluation, diagnosis, and management/treatment of anosmia; and researchers' review of recent advances in potential anosmia treatments from fundamental science, in animal, cellular, or genetic models. As limited evidence-based treatments exist for anosmia, dissemination of information on anosmia-related health risks is needed. This could include feasible and useful screening measures for olfactory dysfunction, appropriate clinical evaluation, and patient counseling to avoid harm as well as manage health and quality of life with anosmia.

Genetics, environmental exposures, and aging interact to produce variations in the perception or liking of taste, olfaction, and somatosensory sensations (i.e., chemosensation). Chemosensory variation can affect disease risk by influencing what people like and choose to eat from abundant supplies of desirable high-fat, sweet, and salty foods and alcoholic beverages at the expense of less-available or less-liked vegetables. We contend that assessing dietary preference via liking–disliking surveys holds promise for linking chemosensation with dietary intake and health outcomes in population-based studies. Typical intake measures (e.g., frequency surveys, dietary records) are difficult to complete and interpret. Because of memory issues and dietary restraint, individuals under- or overreport intakes, leading to inaccurate conclusions about diet–disease relationships. Surveying food and beverage liking is a time-efficient, simple task that minimizes the cognitive limitations of intake measures. In the present study, women in a worksite health risk appraisal completed brief food frequency and liking surveys and reported their height and weight, and blood pressure was measured. While liking and intake measures for high-fat and high-fiber foods were correlated, only liking was associated with disease risk. In multiple regression models, women reporting greater liking for high-fat foods and less liking for spicy foods had greater adiposity and/or blood pressure, controlling for age. These data, along with previous laboratory and community-based studies, support that reported liking of high-fat foods explains variability in adiposity and adiposity-related outcomes. Hedonic measures appear to capture habitual intake of foods and beverages, are easy to implement in the field, and thus may increase understanding of how chemosensory variation modifies disease risk. [ABSTRACT FROM AUTHOR]

Abstract: A half-century ago, Fischer and colleagues found correlations between food preference and genetic markers of taste [6-n-propylthiouracil (PROP), quinine]. Recently, a number of studies report differences in sweet liking/disliking with taste phenotype or genotype. Here we modeled optimal liking for milk/sugar mixtures using the response surface method among 79 mostly normal weight adults (36 women) who reported low dietary restraint. Two non-overlapping phenotype analyses were performed: a) discordance in PROP versus quinine bitterness and b) number of fungiform papillae (FP, taste papillae on the tongue tip). Although all phenotype groups liked highly sweet and creamy sensations (in liking by sensation models), the fat and sugar levels for hedonic optima varied (in liking by concentration models). Males generally liked higher fat (20 to 40%) and sugar levels, with females disliking unsweetened cream. In quinine/PROP groups, liking peaked at 30% fat/15% sucrose for men and women who tasted 0.32 mM quinine more bitter than 3.2 mM PROP (n =15); a group previously shown to have highest sugar intakes (Duffy et al., 2003). Those tasting PROP more bitter than quinine (n =14) reported greater creamy/sweet sensations, with peak liking at lower fat and sweet levels (3.3% fat/10% sucrose). Generally, those in the high FP group perceived more creamy/sweet sensations with level of liking more influenced by sugar level, especially among high FP females. At high sugar/high fat levels low FP males and females retained this liking while liking fell off for those in the high FP group. In summary, although most liked sweet/creamy sensations, perceptual differences in these sensations varied with oral phenotype, explaining some of the differences in the amount of sugar and fat required to reach hedonic optima. A high affinity for high sugar/high fat mixtures among oral phenotype subgroups has relevance for energy consumption and could explain the link previously observed between oral sensation and body weight. [Copyright &y& Elsevier]

Polymorphisms in the TAS2R38 gene provide insight to phenotypes long associated 6-n-propylthiouracil (PROP) and phenylthiocarbamide bitterness. We tested relationships between TAS2R38 genotype, taste phenotype, and fungiform papillae (FP) number in 139 females and 59 males (age range 21–60 years), primarily of European ancestry. DNA was analyzed for 3 polymorphic sites, identifying common (alanine–valine–isoleucine [AVI/AVI], heterozygotes, proline–alanine–valine [PAV/PAV]) and rare (proline–valine–isoleucine, alanine–alanine–valine, AAI) forms. Individuals with PROP threshold >0.15 mM were almost exclusively AVI/AVI; those with threshold <0.1 mM could have any genotype. PAV/PAVs were more difficult to identify with PROP taste measures, although perceived bitterness of moderate PROP concentrations (0.32, 1 mM) had better correspondence with genotype than did threshold. For AVI/AVIs, increases in bitterness from 1 to 3.2 mM PROP nearly paralleled those of TAS2R38 heterozygotes and PAV/PAVs. Some bitterness gains were related to FP number sampled from a standard area on the tongue tip, yet the PROP bitterness–FP relationship differed across genotype. Among homozygotes, FP was a significant determinant of PROP bitterness; heterozygotes showed a flat relationship. Those tasting concentrated PROP as more bitter also tasted concentrated sucrose, citric acid, sodium chloride, and quinine as more intense, even after statistically controlling for TAS2R38 genotype, FP, and intensity of tones (nonoral standard). To summarize, although PROP threshold generally exhibited single-gene complete dominance, PROP bitterness may involve additional bitter receptors as evidenced by misclassification of some nontaster homozygotes and the bitterness functions for concentrated PROP. Variability in receptor expression may explain attenuated bitterness–FP relationships. PROP bitterness does associate with heightened taste sensations (i.e., supertasting), but this is not due to TAS2R38 polymorphisms. [ABSTRACT FROM AUTHOR]

Genetic variation in oral sensation presumably influences ingestive behaviors through sensations arising from foods and beverages. Here, we investigated the influence of taste phenotype [6-n-propylthiouracil (PROP) bitterness, fungiform papillae (FP) density] on sweet and creamy sensations from sugar/fat mixtures. Seventy-nine subjects (43 males) reported the sweetness and creaminess of water or milk (skim, whole, heavy cream) varying in sucrose (0–20% w/v) on the general Labeled Magnitude Scale. Sweetness grew with sucrose concentration and when shifting from water to milk mixtures—the growth was greatest for those tasting PROP as most bitter. At higher sucrose levels, increasing fat blunted the PROP–sweet relationship, whereas at lower levels, the relationship was effectively eliminated. Perceived sweetness of the mixture exceeded that predicted from the sum of components at low sucrose concentrations (especially for those tasting PROP most bitter) but fell below predicted at high concentrations, irrespective of fat level. Creaminess increased greatly with fat level and somewhat with sucrose. Those tasting PROP most bitter perceived greater creaminess in the heavy cream across all sucrose levels. Perceived creaminess was somewhat lower than predicted, irrespective of PROP bitterness. The FP density generally showed similar effects as PROP on sweetness and creaminess, (but to a lesser degree) and revealed potential taste–somatosensory interactions in weakly sweet stimuli. These data support that taste phenotype affects the nature of enhancement or suppression of sweetness and creaminess in liquid fat/sugar mixtures. Taste phenotype effects on sweetness and creaminess likely involve differential taste, retronasal olfactory, and somatosensory contributions to these perceptual experiences. [ABSTRACT FROM AUTHOR]

Alcohol produces a range of oral sensations, some of which have been shown to vary with the perceived bitterness of 6-n-propylthiouracil (PROP), one marker for genetic variation in taste. Some studies report that offspring of alcoholics are most likely to be PROP nontasters [Physiol. Behav. 51 (1992) 1261; Physiol. Behav. 64 (1998) 147], yet others report the offspring as more responsive to sodium chloride (NaCl) and citric acid, which appears to contradict the taste genetic hypothesis. We predicted alcohol sensation and intake from measures of taste genetics (PROP bitterness and number of fungiform papilla), NaCl and citric acid intensity, and spatial taste pattern in 40 females and 43 males. Subjects used the general Labeled Magnitude Scale (gLMS) [Chem. Senses 18 (1993) 683; J. Food Qual. Pref. 14 (2002) 125] as an intensity and hedonic scale. Those who tasted PROP as most bitter or had highest numbers of fungiform papilla reported greatest oral burn from an alcohol probe; those who tasted least PROP bitterness consumed alcoholic beverages most frequently. Although higher NaCl and citric acid ratings associated with more frequent consumption of alcoholic beverages, the findings could be explained by lower intensity of tastants on the tongue tip (chorda tympani nerve) relative to whole mouth perception. In multiple regression analyses, PROP bitterness and the spatial pattern of taste perception were independent contributors to the prediction of alcohol intake. In summary, the results support that variation in oral sensation associates with alcohol intake. Those who taste PROP as least bitter and have low chorda tympani relative to whole mouth taste intensity appear to have fewest oral sensory hindrances to the consumption of alcoholic beverages. [Copyright &y& Elsevier]

We hypothesize that variation in oral sensation influences chronic disease risk by impacting dietary behaviors. Bitterness of 6-n-propylthiouracil (PROP) and fungiform papilla (FP) number serve as genetic taste markers. Data support that nontasters (who taste PROP as least bitter or have lowest FP number) show dietary behaviors that increase CVD risk (e.g. higher alcohol intake, greater preference for and intake of high-fat and sweet foods) and have greater measured CVD risk (e.g. higher blood pressure, less favorable serum lipids). Taste genetics interacts with environmental factors (e.g. taste-related pathologies) to affect oral sensation, dietary behaviors and disease risk. The generalizability of oral sensory and CVD risk relationships has begun to be tested on diverse samples. [Copyright &y& Elsevier]

Abstract: Our sodium-rich food supply compels investigation of how variation in salt sensation influences liking and intake of high-sodium foods. While supertasters (those with heightened propylthiouracil (PROP) bitterness or taste papillae number) report greater saltiness from concentrated salt solutions, the non-taster/supertaster effect on sodium intake is unclear. We assessed taster effects on salt sensation, liking and intake among 87 healthy adults (45 men). PROP bitterness showed stronger associations with perceived saltiness in foods than did papillae number. Supertasters reported: greater saltiness in chips/pretzels and broth at levels comparable to regular-sodium products; greater sensory and/or liking changes to growing sodium concentration in cheeses (where sodium ions mask bitterness) and broths; and less frequently salting foods. PROP effects were attenuated in women. Compared with men, women reported more saltiness from high-sodium foods and greater liking for broth at salt levels comparable to regular-sodium products. Across men and women, Structural Equation Models showed PROP and papillae number independently explained variability in consuming high-sodium foods by impacting salt sensation and/or liking. PROP supertasters reported greater changes in sensation when more salt was added to broth, which then associated with greater changes in broth liking, and finally with more frequent high-sodium food intake. Greater papillae number was associated with less frequent high-sodium food intake via reduced liking for high-fat/high-sodium foods. In summary, variation in sensations from salt was associated with differences in hedonic responses to high-sodium foods and thus sodium intake. Despite adding less salt, PROP supertasters consumed more sodium through food, as salt was more important to preference, both for its salty taste and masking of bitterness. [Copyright &y& Elsevier]

Abstract: Alcoholic beverages are complex stimuli, giving rise to sensations that promote or inhibit intake. Previous research has shown associations between 6-n-propylthiouracil (PROP) bitterness, one marker of genetic variation in taste, and alcohol behaviors. We tested the PROP bitterness and alcohol intake relationship as mediated by tastes of sampled alcoholic beverages. Forty-nine undergraduates (mean age=22 years) participated. According to the Alcohol Use Disorders Identification Test (AUDIT), only 3 of 49 subjects reported patterns indicating problematic drinking. Participants used the general Labeled Magnitude Scale to rate PROP bitterness and tastes from and preference for Pilsner beer, blended scotch whiskey, instant espresso and unsweetened grapefruit juice. Alcohol intake was reported over a typical week. Regression analysis tested the hypothesis that PROP bitterness influenced alcohol bitterness and sweetness, which in turn predicted alcohol intake. Those who tasted less PROP bitterness tasted all beverages as less bitter and more preferred. Sweetness of scotch was significantly greater in those who tasted PROP as least bitter. For scotch, greater sweetness and less bitterness from sampled scotch were direct predictors of greater alcohol intake. For beer, preference ratings were better predictors of alcohol intake than the bitter or sweet tastes of the sampled beer. These findings support that PROP bitterness predicts both positive and negative tastes from alcoholic beverages and that those tastes may predict alcohol intake. The college environment may attenuate direct effects of PROP bitterness and intake. Here, PROP bitterness does not predict alcohol intake directly, but acts instead through sweet and bitter tastes of alcoholic beverages. [Copyright &y& Elsevier]