The alterations of taste and smell in smokers| Tabaccologia

Abstract

Introduction: Alterations in taste and smell due to tobacco smoke are considered side effects. The combustion of a cigarette produces a mixture of chemicals, including known carcinogens and nicotine, which cause damage to the structures involved. Smoking is also associated with a higher rate of oral cavity infections, resulting from oxidative stress and inflammatory responses. This literature review aims to investigate the correlations between cigarette smoking and taste and smell dysfunctions.

Methods: A total of 360 English-language articles based on studies conducted on humans were considered to perform a narrative review.

Results: The examined studies suggest a correlation between tobacco consumption and alterations in the perception of taste and smell. Smokers appear to have a different perception of nicotine compared to non-smokers, with a possible habituation to its bitter taste. Furthermore, smoking cessation can lead to an improvement in taste and smell perception. Smoking cessation is essential to improve the quality of life and reduce tobacco-related disease risks.

Introduction

Alterations in taste and smell due to tobacco smoke are recognized as direct and indirect side effects, associated with one of the leading preventable causes of death worldwide, i.e., lung cancer. There are about 1.1 billion smokers worldwide (21% of the world’s population) aged 15 years and older [1], where lung cancer has become the leading cause of death, surpassing breast cancer [2]. Despite a decreasing trend in the number of smokers, the decline is not occurring at the desired rate. Typically, smoking experimentation begins between the ages of 10 and 15, with regular smoking starting around age 20. The average daily cigarette consumption is decreasing globally but still averages around 11 cigarettes per day per smoker [3]. The combustion of a cigarette produces a complex mixture of chemicals, including known carcinogens such as carbon monoxide and hydrogen cyanide, as well as polycyclic aromatic hydrocarbons (PAHs) like benzo[a]pyrene, naphthalene, and phenanthrene. Additionally, tobacco smoke contains nicotine, a psychotropic substance that causes addiction and is involved in cellular proliferation processes [4]. This mixture has an extremely negative impact on the body, causing both direct and indirect damage to the involved anatomical structures. In particular, a higher rate of oral cavity infections associated with tobacco use has been observed. Tobacco smoke contains chemicals, including reactive oxygen species (ROS) and reactive nitrogen species (RNS), that can damage cellular and subcellular targets such as lipids, proteins, and nucleic acids. The observed damage is attributable to the establishment of oxidative stress and inflammatory response within the oral and respiratory cavities. These phenomena mutually influence each other, creating a vicious cycle that perpetuates the accumulation of reactive oxygen species (ROS) [5]. This accumulation poses a potential increase in damage to macromolecular targets, with consequent risks of numerous pathologies, including cancer. Despite worldwide efforts to discourage tobacco smoking, lung cancer is associated with more than 9.5 million deaths in 2018 alone, with nearly 30% of all cancer deaths in the USA attributed to it, and approximately 80% of lung cancers linked to smoking. The purpose of this literature review is to conduct an investigation comparing data from studies available on the PubMed and Web of Science platforms from 1980 to the present, highlighting the association between cigarette smoking and taste and smell dysfunctions, which, if identified early, can be symptoms of more severe diseases such as Alzheimer’s and Parkinson’s disease, as well as more recent diseases like COVID-19, which, as already known, have anosmia and ageusia as unmistakable symptoms. Tobacco is one of the leading causes of damage to the oral cavity, with significant impacts on taste (Figure 1) and smell. Smokers are more prone to gum problems such as periodontitis, tooth loss, and gum recession. This is due to smoking’s tendency to weaken the body’s defenses and intensify inflammatory reactions, leading to direct and indirect damage to anatomical structures involved. Furthermore, smoking increases the risk of oral cancer, with a significant percentage of tumors attributed to this habit [6]. Nicotine contained in tobacco has a bitter taste and can influence taste perception. Taste receptors can be compromised by smoking, causing a decreased sensitivity to certain flavors and the need to increase dosages to perceive them [7]. This phenomenon can contribute to smokers’ eating habits. Smell is also severely affected by tobacco smoke. Smokers have a higher risk of developing olfactory dysfunctions, with chronic inflammation of the respiratory tract and the replacement of healthy olfactory epithelium with squamous epithelium [8]. However, smoking cessation can lead to an improvement in smell in many cases. Furthermore, smoking causes morphological changes in central neural pathways involved in olfactory function, with the olfactory bulb and gray matter associated with the olfactory cortex potentially suffering damage. Although not all damage may be reversible, smoking cessation can reduce some of the olfactory dysfunctions caused by tobacco [9].

Methods

The investigation was conducted with the aim of examining meta-analysis studies addressing the effect of smoking on the senses of smell and taste. English-language articles based on studies conducted in humans were considered. Among them, the meta-analysis by Da Ré et al. 2018 [10] met all inclusion criteria, with the most important one being that all studies included in the meta-analysis examined the relationship between smell, taste, and smoking. The search covered articles published from January 1980 to August 2014 in the following databases: MEDLINE (accessed through PubMed), LILACS, Cochrane Library, and SciELO. Two separate lines of research were conducted: one focused on smell and the other on taste. Keywords used for the search included “Smoking,” “Randomized Controlled Trial,” “Smell Disorders,” “Smell,” “Sensory Modalities,” “Odor,” along with their MeSH terms. The selected search terms related to taste were “Smoking,” “Randomized Controlled Trial,” “Taste Disorders,” “Taste,” “Dysgeusia,” “Ageusia,” and their MeSH terms. Words related to outcome measures were not included to increase the sensitivity of this research. Exclusion criteria were applied to studies that did not show a clear methodological definition and those whose main outcome was not centered on the subjects’ smell or taste. Four articles were selected. Of the four studies included, only one considered both senses simultaneously (smell and taste) [11]. Two studies [12,13] focused exclusively on smell, while another study [14] considered only changes related to taste.

Results

The first study [11] involved 15 male and female smokers with an average age of 38.8 years and an average daily consumption of 6 cigarettes. It sought to determine whether the perception of puff strength was related to the amount of nicotine delivered and whether the sense of smell could discriminate nicotine. The second study [12] This study included 30 male volunteers with an average age of 29.9 years, of whom 15 were smokers of at least 20 cigarettes a day for two years, and the others were non-smokers. The study examined the role of smell and the trigeminal system in nicotine discrimination between smokers and non-smokers. The results showed that smokers considered nicotine less unpleasant than non-smokers. The third study [13] involved 48 daily cigarette smokers of both sexes. It examined the effects of short-term smoking abstinence and acute nicotine administration on taste perception in smokers, influencing eating behavior. The authors found that smoking abstinence and the type of cigarette influenced taste perception (Figure 2). Non-abstinent smokers rated sucrose as more pleasurable than salty solutions, while there were no significant differences among abstainers. The fourth study [14] involved 581 daily smokers divided into two groups: those who continued to smoke for two weeks and those who abstained for at least seven days. The study aimed to assess whether smoking withdrawal symptoms, including smell and taste, were valid signals of cigarette abstinence. The results showed that withdrawal symptoms, including loss of smell and taste, improved immediately after smoking cessation. In general, these studies suggest that smoking can influence both smell and taste, but further research is needed to fully understand the impact of smoking on these senses.

The mechanisms through which smoking damages smell and taste are still under study, but some known causes include squamous metaplasia, in which the airway epithelium is irreversibly replaced by another type of epithelium [8]. Furthermore, tobacco smoke exposure has been linked to increased apoptosis of olfactory neurons, but the continuous cellular turnover of the olfactory epithelium allows for constant regeneration of its functions after smoking cessation [15]. Smoking causes reversible sinonasal inflammation, associated with olfactory dysfunction, and the treatment of this condition and smoking cessation lead to an improvement in smell [16]. Some studies have also highlighted morphological changes in central neural pathways involved in olfactory function, such as reduced volume of the olfactory bulb and gray matter in the olfactory gyrus of heavy smokers, suggesting that such changes may precede olfactory dysfunctions [9]. Additionally, the bitterness of nicotine in humans activates specific taste receptors, eliciting an excitatory response in neurons involved in bitter taste while simultaneously suppressing responses to sweet, sour, salty, and umami flavors [7]. Smoking can negatively affect flavor perception due to changes in the oral plaque microbiome, xerostomia, reduced salivary flow, and alterations in the typical oral hygiene of smokers [17]. Furthermore, it has been found that smoking is associated with a deterioration of the sense of taste, particularly the inability to perceive bitterness. Nicotine in tobacco smoke appears to influence taste receptors, altering the responses of neurons related to bitter taste and suppressing the perception of flavors such as sweet, sour, salty, and umami [18]. In summary, studies suggest an association between smoking and taste and smell dysfunction, with effects on neural structures involved in these functions.

Conclusions

In this literature review, it has been reported that olfactory and taste dysfunctions are consistently present, directly or indirectly, in individuals who smoke nicotine-containing products such as cigars and cigarettes. However, current means of assessing the quality of taste and smell are not sufficiently precise. Nevertheless, it is known that smoking causes direct and indirect damage to the oral cavity and respiratory pathways, altering the perception of flavors and odors. The reduction in olfactory and gustatory capacities due to smoking can lead to increased health risks, such as difficulty in discerning spoiled or hazardous foods. It is also important to note that anosmia and ageusia have been significant symptoms for the recognition and identification of COVID-19 during the pandemic.

However, it has been reported that quitting smoking can lead to partial regeneration of olfactory functions and potentially improved taste perception (Figure 3). Therefore, smoking cessation is essential for enhancing the quality of life and reducing the risks of tobacco-related diseases.

Further studies are hoped for in the field of potential damages caused by cigarette smoking, as well as increased research into potential harms arising from the use of electronic cigarettes and heated tobacco products. Additionally, the importance of more careful medical monitoring of sensory capacities from a young age is emphasized, as such dysfunctions can serve as early indicators of serious illnesses.

Figures and tables

Figure 1.Tongue taste.

Figure 2.Anatomy of a taste bud.

Figure 3.The “Bean Eater” by Annibale Carracci (1583-1584, Colonna Gallery, Rome) masterfully captures the essence of gustatory anticipation. Depicting a commoner eagerly consuming a bowl of beans, Carracci skillfully conveys an anticipation of specific joy before the food reaches the taste buds. The lively expression of the painted man reveals a moment of pure sensory pleasure anticipation, unveiling the expectation even before the actual taste comes into play. The painting thus becomes a representation of that moment of anticipation and pleasure that the act of eating can evoke.

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