Gustatory function and dietary habits in users and nonusers of smokeless tobacco

Smokeless tobacco use and public health nutrition: a global systematic review

OBJECTIVE

Tobacco consumption among low- and middle-income countries where food insecurity remains a challenge poses several concerns. This review examines the available global evidence linking smokeless tobacco (SLT) use with public health nutrition and its implications.

DESIGN

Systematic review of articles extracted from PubMed and Scopus from January 2000 to December 2020.

SETTING

Included studies that demonstrated the relationship between SLT and nutrition-related factors, that is, BMI, malnutrition, anaemia, poor birth outcomes and metabolic disorders. Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) guidelines have been followed to conduct the systematic evidence review.

PARTICIPANTS

A total of thirty-four studies were finally used in the systematic review, which included cross-sectional (thirty-one) and cohort (three).

RESULTS

SLT use has a huge impact on body weight, alteration in taste, poor oral health, and consumption of fruits and vegetables leading to malnutrition. Maternal use of SLT not only leads to anaemia but also hampers birth outcomes. Increased risk of metabolic syndrome and gallstone disease among SLT users are also well documented in the studies.

CONCLUSION

The review highlights the linkages between SLT usage and poor nutritional outcomes. Tobacco control efforts should be convergent with public health nutrition to achieve overall health benefits. Attention is also required to explore suitable mechanisms for SLT cessation combined with enhancing food and nutrition security at the community level in sync with investments in public health nutrition intervention.

Inter-individual characteristics on basic taste recognition thresholds in a college-aged cohort: potential predictive factors

Studying nutritional status from the perspective of taste sensitivity, rather than only dietary patterns, may provide new insights into the role of taste receptor signaling in the development of metabolic-associated diseases. In this cross-sectional study, we investigated the possible influence of sociodemographic (sex and smoking habit) and clinical variables (dental cavities, missing teeth, sinusitis, rhinitis, body mass index and metabolic high prevalence family antecedent diseases) on tastant (sucrose, monosodium glutamate, sodium chloride, citric acid, quinine, sinigrin, phenylthiocarbamide) recognition thresholds (RTs) in a college-aged cohort (n = 397). Predictive models for the tastant RTs were generated and a higher sucrose RT was found in females than in males, while sinusitis and rhinitis explained sucrose and sodium chloride RTs. Smoking habit was not an important predictive factor of taste sensitivity, although its long-term influence on RTs remains unclear. Additionally, a positive correlation was found between all the tastant RTs studied. Although results did not show a clear pattern, the statistical approach employed should prove useful in future studies of predictors of taste sensitivity.

Effect of cigarette smoke on gustatory sensitivity, evaluation of the deficit and of the recovery time-course after smoking cessation

BACKGROUND

Study results have shown that chronic exposure to cigarette smoke affects the taste function in humans. However, neither the quantitative impact on taste sensitivity nor the time-course of taste recovery on stopping smoking have been precisely examined.

METHODS

The experimental design included 2 phases, (i) a case-control phase comparing the taste sensitivity level measured by Electrogustometric (EGM) thresholds from various parts of the tongue (locus) between smokers (n = 83) and non-smokers (n = 48), (ii) a follow-up study looking at the taste sensitivity recovery in smokers after smoking cessation (n = 24) and compared with non-smokers.

RESULTS

Smokers exhibited significantly lower taste sensitivity than non-smokers - the higher the nicotine dependence (Fagerström scores), the lower the taste sensitivity. After smoking cessation, EGM thresholds decreased progressively, and reached the taste sensitivity range of non-smokers depending on locus and time. After 2 weeks a recovery could be observed on the 3 Tip and the 2 edge loci; the recovery in the posterior loci was complete after 9 weeks, and in the dorsal loci recovery was observed only after 2 months or more.

CONCLUSIONS

Smoking cessation does lead to a rapid recovery of taste sensitivity among smokers, with recovery time found to differ based on the sensitivity of loci of the tongue. The use of EGM could potentially be explored as a motivational tool for smoking cessation.

Amiloride-sensitive sodium currents in fungiform taste cells of rats chronically exposed to nicotine

Many studies have demonstrated that chronic exposure to nicotine, one of the main components of tobacco smoke, has profound effects on the functionality of the mammalian taste system. However, the mechanisms underlying nicotine action are poorly understood. In particular no information is available on the chronic effect of nicotine on the functioning of taste cells, the peripheral detectors which transduce food chemicals into electrical signals to the brain. To address this issue, I studied the membrane properties of rat fungiform taste cells and evaluated the effect of long-term exposure to nicotine on the amiloride-sensitive sodium currents (ASSCs). These currents are mediated by the epithelial sodium channels (ENaC) thought to be important, at least in part, in the transduction of salty stimuli. Patch-clamp recording data indicated that ASSCs in taste cells from rats chronically treated with nicotine had a reduced amplitude compared to controls. The pharmacological and biophysical analysis of ASSCs revealed that amplitude reduction was not dependent on changes in amiloride sensitivity or channel ionic permeability, but likely derived from a decrease in the activity of ENaCs. Since these channels are considered to be sodium receptors in taste cells, my results suggest that chronic exposure to nicotine hampers the capability of these cells to respond to sodium ions. This might represent a possible cellular mechanism underlying the reduced taste sensitivity to salt typically found in smokers.

Lower expressions of the human bitter taste receptor TAS2R in smokers: reverse transcriptase-polymerase chain reaction analysis

Background

Despite the fact that smokers have deficit in detecting taste, particularly bitter taste, no study has investigated its biological correlate.

Methods

In this context, we compared the expression of the bitter taste receptor gene, taste 2 receptor (TAS2R) in the tongues of smokers and non-smokers. Tissue samples were collected from the lateral portion of the tongues of 22 smokers and 22 age- and gender-matched healthy volunteers (19 males and three females) with no history of smoking. Reverse transcriptase-polymerase chain reaction was used to examine the expression of TAS2R in the two groups, and the effect of aging on TAS2R expression was also assessed.

Results

TAS2R expression was significantly lower among smokers than non-smokers (t = 6.525, P < .0001, 11.36 ± 6.0 vs. 2.09 ± 2.8, mean ± SD, non-smokers vs. smokers). Further, a positive correlation between age and expression of TAS2R was observed in non-smokers (r = .642, P = .001), but not smokers (r = .124, P = .584). This correlation difference was significant (Z = 1.96, P = .0496).

Conclusions

Smokers showed a significantly lower expression of the bitter taste receptor gene than non-smokers, which is potentially caused by their inability to acquire such receptors with age because of cigarette smoking, in contrast to non-smokers.

Effects of acute abstinence and nicotine administration on taste perception in cigarette smokers

We investigated the effects of short-term abstinence from smoking and acute nicotine administration on taste perception in smokers. We assessed sensitivity for salt and sucrose solutions and the self-reported intensity and pleasantness of these tastes, using a previously validated model of taste perception. This was in order to investigate mechanisms by which cigarette smoking and smoking cessation may modulate dietary behaviour. Male and female daily smokers attended a single testing session. Participants were randomised to either abstain for smoking for 12 h or smoke as usual on the morning of testing. At the testing session, participants completed subjective ratings of mood and ratings of intensity and pleasantness of salt and sucrose solutions, followed by measurement of the threshold at which these solutions could be detected on the tongue. Participants were then randomised to smoking either a nicotine-containing or denicotinised cigarette, after which they completed the same measures as previously. Our data suggest that following cigarette smoking, lower taste thresholds are obtained after smoking a denicotinised cigarette compared with a nicotinised cigarette, but among females only. This effect was not observed among males and did not differ as a function of abstinence condition. In addition, among non-abstinent smokers, females demonstrated higher taste thresholds (i.e. reduced sensitivity) for salt than males, but this sex difference was not observed among abstinent smokers.

Effects of cigarette smoking and family history of alcoholism on sweet taste perception and food cravings in women

BACKGROUND

Despite popular beliefs that smoking affects the sensitivity and liking of sweet-tasting foods and beverages, few psychophysical studies have examined this phenomenon and none have taken into account the individual's family history of alcoholism (FH+), a predictor of heightened sweet preferences.

METHODS

A within- and between-subjects study was conducted to determine the effect of both cigarette smoking and an acute exposure to nicotine on sweet taste sensitivity and preferences in women. Two groups were studied on 2 days separated by 1 week: women who were current smokers (n = 27, 18 were FH+) and those who never smoked in their lifetime (n = 22, 9 were FH+). Current smokers smoked nicotine-containing cigarettes during 1 test session and nicotine-free cigarettes during the other. The procedures were identical during both test sessions for the group of never smokers, with the exception that they did not smoke. Two-alternative staircase methods and forced-choice tracking procedures were used to assess sucrose thresholds and preferences, respectively, during both test session. Standardized questionnaires were administered to assess food cravings as well as smoking and alcohol usage and dependence. The Family Interview for Genetic Studies was used to detect alcoholism according to the DSM III criteria for family members up to second-degree relatives.

RESULTS

Acute exposure to nicotine did not affect sucrose detection thresholds or preferences, but smokers had significantly higher sucrose detection thresholds than never smokers. The greater the smoking dose in pack-years, the lower the sucrose sensitivity. Regardless of smoking status, women who were FH+ preferred significantly higher sucrose concentrations and craved sweets more often than women who were not.

CONCLUSIONS

Both smoking and having a family history of alcoholism had differential effects on sweet taste. Smoking was associated with decreased sweet taste sensitivity whereas having a family history of alcoholism was associated with heightened sweet preferences. These findings suggests that future research on the effects of smoking on food habits and cravings should take into account family history of alcoholism given its association with sweet liking and the increased likelihood to develop a tobacco disorder.

Effect of nicotine on chorda tympani responses to salty and sour stimuli

The effect of nicotine on the benzamil (Bz)-insensitive (transient receptor potential vanilloid-1 variant cation channel, TRPV1t) and the Bz-sensitive (epithelial Na(+) channel, ENaC) salt taste receptors and sour taste was investigated by monitoring intracellular Na(+) and H(+) activity (pH(i)) in polarized fungiform taste receptor cells (TRCs) and the chorda tympani (CT) nerve responses to NaCl, KCl, and HCl. CT responses in Sprague-Dawley rats and both wildtype and TRPV1 knockout (KO) mice were recorded in the presence and absence of agonists [resiniferatoxin (RTX) and elevated temperature] and an antagonist (SB-366791) of TRPV1t, the ENaC blocker (Bz), and varying apical pH (pH(o)). At concentrations <0.015 M, nicotine enhanced and at >0.015 M, it inhibited CT responses to KCl and NaCl. Nicotine produced maximum enhancement in the Bz-insensitive NaCl CT response at pH(o) between 6 and 7. RTX and elevated temperature increased the sensitivity of the CT response to nicotine in salt-containing media, and SB-366791 inhibited these effects. TRPV1 KO mice demonstrated no Bz-insensitive CT response to NaCl and no sensitivity to nicotine, RTX, and elevated temperature. We conclude that nicotine modulates salt responses by direct interaction with TRPV1t. At pH(o) >8, the apical membrane permeability of nicotine was increased significantly, resulting in increase in TRC pH(i) and volume, activation of ENaC, and enhancement of the Bz-sensitive NaCl CT response. At pH(o) >8, nicotine also inhibited the phasic component of the HCl CT response. We conclude that the effects of nicotine on ENaC and the phasic HCl CT response arise from increases in TRC pH(i) and volume.

Long-term effects of nicotine on rat fungiform taste buds

Nicotine, an alkaloid found in tobacco smoke, has been recognized as capable of inducing changes in taste functionality in conditions of chronic exposure. The mechanisms underlying these sensory alterations, however, are currently unknown. We addressed this issue by studying the long-term effects of nicotine on the anatomical features of taste buds, the peripheral end-organs of taste, in rat fungiform papillae. Nicotine was administered to rats via drinking water over a period of 3 weeks, which represents a standard method to achieve chronic drug exposure in laboratory animals. We found that prolonged administration of nicotine induced a significant reduction in the size of fungiform taste buds, without affecting their total number on the rat tongue. Morphometric measurements as well as evaluations of taste cell membrane capacitance suggested that the reduced size of taste organs was determined by a decrease in the number of cells per taste bud. In addition, chronic treatment with nicotine caused an increase in the relative density of cells expressing gustducin, a specific G protein alpha-subunit found in some taste cells and involved in bitter/sweet transduction. Interestingly, changes in the expression pattern of gustducin turned out to be more pronounced in periadolescent/adolescent than in adult rats. As a whole, our data indicate that long-term nicotine administration induces significant changes in the anatomical properties of taste buds in rat fungiform papillae. These changes could have a profound impact on the sensory information relayed to the brain; therefore, they may be responsible, at least in part, for the alterations in taste functionality observed during chronic nicotine exposure, a condition found in regular smokers.

Effects of tobacco smoking on caloric intake

Reduced body weight due to smoking may be an important factor inhibiting smoking cessation and promoting relapse after cessation in some smokers. It is popularly believed that smoking decreases body weight by suppressing appetite. However, cross-sectional studies show that, despite their lower body weights, smokers do not eat less than non-smokers or ex-smokers and, in fact, tend to eat slightly more. Similarly, laboratory studies show no acute effects of smoking or nicotine intake via other means on caloric intake in smokers, although intake of non-smokers may be reduced after nicotine. In contrast, longitudinal studies show that eating consistently increases in the first weeks after stopping smoking, but may recede to pre-cessation levels with longer-term abstinence, while resumption of smoking after cessation is accompanied by a reduction in eating. A similar pattern of results is seen for self-reported hunger and some, but not all, constituents of diet. Thus, there appear to be no acute or chronic effects of smoking on eating in smokers maintaining regular smoking, but changes in eating are observed concomitant with changes in smoking status (i.e. cessation or relapse). Although tolerance to anorectic effects of nicotine is one potential explanation, these findings may be more parsimoniously explained by viewing changes in eating due to smoking as secondary to an alteration in the set point around which body weight is regulated. According to this notion, cessation is accompanied by increased eating only until a new, higher body weight set point is reached, while relapse (and perhaps initiation of smoking) decreases eating only until a lower set point is reached. Implications of these findings and a set point explanation for them are discussed.

Effects of nicotine on hunger and eating in male and female smokers

We tested whether the inverse relationship between smoking and body weight may be due in part to nicotine's acute effects on reducing hunger and eating. On four mornings, male and female smokers (n = 10 each), abstinent overnight from smoking and food, received one of three nicotine doses (7.5, 15, and 30 micrograms/kg) or placebo (0) via nasal spray every 30 min for 2 h. Self-reported hunger and satiety ("fullness") and craving for cigarettes were obtained after each dose presentation. Subjects subsequently ate ad lib from a large array of food items varying in sweet taste and fat content. For both males and females, nicotine had no effect on self-reported hunger, but cigarette craving was decreased. Rather than being decreased, caloric intake during the meal was unexpectedly increased following nicotine compared with placebo. Cigarette craving increased after the meal, and this increase was unaffected by nicotine dose. There were virtually no differences between males and females in any effects of nicotine. These results indicate that nicotine may not acutely suppress appetite in fasting smokers and suggest that other actions of nicotine or smoking may account for the lower body weights of smokers.

Evaluation of risk factors in smokeless tobacco-associated oral lesions

Smokeless tobacco (ST) users and nonusers were recruited to evaluate the contribution of various risk factors (ST use, cigarettes, alcohol, and diet) in the development of oral mucosal lesions. Ninety-eight ST users with no lesion, 29 ST users with an oral lesion, and 33 nonusers were enrolled in the study. ST users with lesions, when compared with users with no lesion, were more likely to have used snuff than chewing tobacco (p = 0.01) and to have used more ST (p less than 0.01). Alcohol consumption, dietary intake of beta-carotene, and serum levels of beta-carotene were not related to an increased risk of lesion development. Our findings showed that the only significant risk factor for ST-associated oral lesions was the extent of ST exposure. Of 127 ST users, 29 (22.8%) had an oral lesion at the time of examination. Of these lesions, 23 (79.3%) were hyperkeratotic and 6 (20.7%) were epithelial dysplasia.