Smoking and olfactory dysfunction: A systematic literature review and meta-analysis

Olfaction in pregnancy: systematic review and meta-analysis

Little attention has been paid to olfactory changes during pregnancy with contemporary studies limited in number and sample size. We examined whether pregnancy is associated with differences in olfactory performance and if there were any specific gestational ages at which these differences occur through a comprehensive systematic review and meta-analysis of the current literature. An initial electronic database search identified 234 citations, which were screened at the abstract level. Twenty-three citations were germane for full-text review, and 13 met criteria for inclusion. Our review assessed 5 olfactory measures of interest: odor identification (n = 11 articles), threshold (n = 8), discrimination (n = 5), hedonics (n = 6), and intensity (n = 5). Nine of these 13 studies contained sufficient data for meta-analysis, and these studies included a total of 523 pregnant women and 365 non-pregnant controls. Despite previous subjective and objective reports of odor intolerances and odor hypersensitivity, we did not find any significant differences between pregnant and non-pregnant women in odor discrimination, thresholds, or hedonics. However, meta-analysis of 506 cases and 333 controls showed worse odor identification in pregnant women compared to controls in a random-effects model. Thus, we demonstrate worse performance at odor identification during pregnancy. In this review, we discuss the current evidence (and lack thereof) regarding olfaction in pregnancy as well as highlight current knowledge gaps in this field.

Olfaction in COPD

BACKGROUND

Olfaction is poorly characterized in COPD. To test the hypothesis that olfaction is reduced in COPD, we assessed olfaction with the "Sniffin' Sticks" test and a questionnaire addressing olfaction in COPD and a corresponding control group in respect to age and sex. We also explored whether there is an association between COPD, chronic rhinosinusitis without nasal polyps (CRSsNP), and other predefined covariates with olfactory function.

METHODOLOGY

Olfactory function was assessed by the score for threshold (T), discrimination (D) and identification (I), and the composite TDI score in the "Sniffin' Sticks" test and by self-reported evaluation of impaired olfaction and of "decreased sense of smell and taste" in the 22-item Sino-Nasal Outcome Test (SNOT-22) in 90 COPD patients and 93 controls. A clinical interview and ENT-examination with nasal endoscopy, skin prick test and spirometry with reversibility were performed.

RESULTS

The TDI, D and I scores were significantly lower in the COPD group than in the control group. The T score was not significantly different between the two groups. Hyposmia and anosmia were present in up to 79% of patients with COPD. The prevalence of self-reported impaired olfactory function and for "decreased sense of smell and taste" - was more than two-fold greater in the COPD than in the control group. COPD, higher age, male sex and allergy were associated with a lower TDI score, while CRSsNP was not associated with the TDI score.

CONCLUSIONS

COPD is associated with olfactory dysfunction and the underlying mechanisms for this dysfunction should be elucidated.

Olfactory dysfunction in passive vs active smoking

BACKGROUND

The aim of this study is to assess the olfactory functions of passive smokers compared to active smokers and nonsmokers.

METHODS

This prospective case-control study included 30 nonsmokers, 30 passive smokers, and 30 active smoker participants. All groups were matched for gender and age. The Sino-Nasal Outcome Test 22 (SNOT-22) and Sniffin' Sticks test battery were administered to all subjects. Threshold (T), discrimination (D), and identification (I) scores were noted. Olfactory function was subjectively assessed as 0: severe dysfunction and 5: no problem.

RESULTS

Overall, TDI scores of active smokers (24.78 ± 3.02) and passive smokers (24.90 ± 2.45) were significantly lower than nonsmokers (34.23 ± 3.46). There was no statistically significant difference between passive smokers and smokers (F (2,87) = 13.47, P < .001)). All subscores are negatively affected by active or passive smoking. The greatest impact of smoking was on threshold scores (η 2 T  = 0.719), followed by identification (η 2 I  = 0.353) and discrimination (η 2 D  = 0.282) scores. SNOT-22 and TDI scores were weakly (r = -.352) correlated as subjective assessment, and TDI scores were moderately correlated (r: .539) (P values < .001). Age and pack-years cigarette dosage had a negative effect on the TDI score (TDI = 26.386 - (0.084 × age) - (0.072 × Pack.Year)) according to stepwise linear regression model (F = 10.187; P = .001).

CONCLUSIONS

Passive smoking has nearly the same adverse effect on olfactory function as active smoking. The threshold scores are the most negatively affected. The olfactory effect of cigarette smoke may not be directly related to nasal inflammation. Olfactory neuronal pathways should be investigated to elucidate the exact pathophysiology.

LEVEL OF EVIDENCE

3b.

Association between social determinants of health and olfactory function: a scoping review

BACKGROUND

Social determinants of health (SDoH) include the socioeconomic, demographic, and social conditions that influence differences in health status among individuals and groups. The impact of these conditions on olfactory function remains poorly understood. In this scoping review, we systematically review the available literature to synthesize the association between SDoH and olfactory function.

METHODS

In accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses extension for Scoping Review (PRISMA-ScR) guidelines, we performed systematic search queries in PubMed, Embase, and Ovid databases and categorized articles according to themes that emerged regarding SDoH. The primary outcomes included self-reported and objective measurements of smell.

RESULTS

We identified 722 unique references that underwent title and abstract review by two independent reviewers, with 70 articles undergoing full-text review and 57 relevant for data extraction. Six themes emerged in our review, under which we categorized the studies and synthesized respective associations with olfactory function. These include studies exploring socioeconomic status (n = 19, 33%), education status (n = 27, 47%), occupational exposures (n = 26, 46%), racial/ethnic disparities (n = 12, 21%), and lifestyle/behavioral factors (n = 33, 58%).

CONCLUSIONS

Within the context of this scoping review, olfactory dysfunction is significantly more prevalent in patients with lower socioeconomic status, exposure to environmental and occupational toxins, and of minority race/ethnicity, whereas the associations between olfactory dysfunction and education level and lifestyle factors such as smoking and drinking seem to be much more elusive. This review highlights the importance of accounting for SDoH in observational studies examining olfactory outcomes. Given the increased awareness of olfactory loss, special consideration should be given to understanding olfactory dysfunction in the context of these factors.

Lipidomic profile of human nasal mucosa and associations with circulating fatty acids and olfactory deficiency

The nasal mucosa (NM) contains olfactory mucosa which contributes to the detection of odorant molecules and the transmission of olfactory information to the brain. To date, the lipid composition of the human NM has not been adequately characterized. Using gas chromatography, liquid chromatography coupled to mass spectrometry and thin layer chromatography, we analyzed the fatty acids and the phospholipid and ceramide molecular species in adult human nasal and blood biopsies. Saturated and polyunsaturated fatty acids (PUFAs) accounted for 45% and 29% of the nasal total fatty acids, respectively. Fatty acids of the n-6 family were predominant in the PUFA subgroup. Linoleic acid and arachidonic acid (AA) were incorporated in the main nasal phospholipid classes. Correlation analysis revealed that the nasal AA level might be positively associated with olfactory deficiency. In addition, a strong positive association between the AA levels in the NM and in plasma cholesteryl esters suggested that this blood fraction might be used as an indicator of the nasal AA level. The most abundant species of ceramides and their glycosylated derivatives detected in NM contained palmitic acid and long-chain fatty acids. Overall, this study provides new insight into lipid species that potentially contribute to the maintenance of NM homeostasis and demonstrates that circulating biomarkers might be used to predict nasal fatty acid content.

Olfaction in patients with Parkinson's disease: a new threshold test analysis through turning points trajectories

Olfactory deficit is a widely documented non-motor symptom in Parkinson’s disease (PD). Abnormal turning points trajectories through olfactory threshold testing have been recently reported in patients with olfactory dysfunction, who seem to adapt faster to olfactory stimuli, but data on PD patients are lacking. The aim of this study is to perform olfactory threshold test and explore the turning points trajectories in PD patients in comparison to normal controls. We recruited 59 PD patients without dementia, and no conditions that could influence evaluation of olfaction and cognition. Sixty healthy subjects served as controls. Patients and controls underwent a comprehensive olfactory evaluation with the Sniffin’ Sticks extended test assessing threshold, discrimination and identification and a full neuropsychological evaluation. Besides, threshold test data were analyzed examining all the turning points trajectories. PD patients showed a different olfactory threshold test pattern, i.e., faster olfactory adaptation, than controls with no effect of age. Normosmic PD patients showed different olfactory threshold test pattern, i.e., better threshold score, than normosmic controls. Visuospatial dysfunction was the only factor that significantly influenced this pattern. Olfactory threshold trajectories suggested a possible adaptation phenomenon in PD patients. Our data offered some new insights on normosmic PD patients, which appear to be a subset with a specific psychophysical profile. The analysis of the turning points trajectories, through an olfactory threshold test, could offer additional information on olfactory function in PD patients. Future larger studies should confirm these preliminary findings.

Does Each Menstrual Cycle Elicit a Distinct Effect on Olfactory and Gustatory Perception?

The obesity pandemic has brought forth a scientific interest in food intake and sensory perception interactions. Olfactory perception and gustatory perception are very complex and under the influence of many factors, including the menstrual cycle. This study aims to clarify conflicting findings on the influence of the menstrual cycle on olfactory and gustatory perception. Women were assessed during four consecutive phases of one complete cycle (mid-follicular, ovulatory, mid-luteal, and late luteal phases (N = 21)), in contrast to women measured across the same phases belonging to two menstrual cycles (N = 29). Additional control groups were men (N = 17), postmenopausal women (N = 14), oral contraceptive users (N = 10), and women with an anovulatory cycle (N = 8). Olfactory threshold, odor discrimination, and identification were tested using the "Sniffin Sticks" test kit. Suprathreshold intensity and hedonic ratings for sweet, salty, sour, and bitter solutions were assessed. One-way ANOVA and ANOVA for repeated measurements was applied in the analysis, along with linear and trigonometric data fitting and linear mixed models. Linear increases in olfactory discrimination, identification, and overall olfactory performance were observed only in women followed across a complete menstrual cycle. Compared to other groups, these women displayed a cyclic pattern characterized by a predilection for sweet solution; reduced distaste for salty and sour solutions; and increased intensity perception of salty, sour, and bitter solutions towards the end of the cycle. These results suggest that a distinct hormonal milieu of a complete menstrual cycle may be affecting both olfactory and gustatory perception.

Olfactory Impairment Among Rural-Dwelling Chinese Older Adults: Prevalence and Associations With Demographic, Lifestyle, and Clinical Factors

Objective: Olfactory impairment (OI) refers to decreased (hyposmia) or absent (anosmia) ability to smell. We sought to estimate the prevalence and correlates of OI among rural-dwelling Chinese older adults.

Methods: This population-based cross-sectional analysis included 4,514 participants (age ≥65 years; 56.7% women) from the Multidomain Interventions to Delay Dementia and Disability in Rural China (MIND-China). The 16-item Sniffin' Sticks identification test (SSIT) was used to assess olfactory function. Olfactory impairment was defined as the SSIT score ≤10, hyposmia as SSIT score of 8–10, and anosmia as SSIT score <8. Multivariable logistic regression models were used to examine factors associated with OI.

Results: The overall prevalence was 67.7% for OI, 35.3% for hyposmia, and 32.5% for anosmia. The prevalence increased with age for OI and anosmia, but not for hyposmia. The multivariable-adjusted odds ratio (OR) of OI was 2.10 (95% CI 1.69–2.61) for illiteracy and 1.41 (1.18–1.70) for elementary school (vs. middle school or above), 1.30 (1.01–1.67) for current smoking (vs. never smoking), 0.86 (0.74–0.99) for overweight and 0.73 (0.61–0.87) for obesity (vs. normal weight), 4.21 (2.23–7.94) for dementia, 1.68 (1.23–2.30) for head injury, and 1.44 (1.14–1.83) for sinonasal disease. Illiteracy in combination with either male sex or diabetes was significantly associated with an over two-fold increased OR of OI (p for interactions <0.05).

Conclusion: Olfactory impairment is highly prevalent that affects over two-thirds of rural-dwelling older adults in China. OI is correlated with illiteracy, current smoking, dementia, head injury, and sinonasal disease, but negatively associated with overweight or obesity. Olfactory impairment as a potential clinical marker of neurodegenerative disorders among older adults deserves further investigation.

Age-Related Changes in Clinical Presentation of Covid-19: the EPICOVID19 Web-Based Survey

BACKGROUND

The influence of aging and multimorbidity on Covid-19 clinical presentation is still unclear.

OBJECTIVES

We investigated whether the association between symptoms (or cluster of symptoms) and positive SARS-CoV-2 nasopharyngeal swab (NPS) was different according to patients' age and presence of multimorbidity.

METHODS

The study included 6680 participants in the EPICOVID19 web-based survey, who reported information about symptoms from February to June 2020 and who underwent at least one NPS. Symptom clusters were identified through hierarchical cluster analysis. The associations between symptoms (and clusters of symptoms) and positive NPS were investigated through multivariable binary logistic regression in the sample stratified by age (<65 vs ≥65 years) and number of chronic diseases (0 vs 1 vs ≥2).

RESULTS

The direct association between taste/smell disorders and positive NPS was weaker in older and multimorbid patients than in their younger and healthier counterparts. Having reported no symptoms reduced the chance of positive NPS by 86% in younger (95%CI: 0.11-0.18), and by 46% in older participants (95%CI: 0.37-0.79). Of the four symptom clusters identified (asymptomatic, generic, flu-like, and combined generic and flu-like symptoms), those associated with a higher probability of SARS-CoV-2 infection were the flu-like for older people, and the combined generic and flu-like for the younger ones.

CONCLUSIONS

Older age and pre-existing chronic diseases may influence the clinical presentation of Covid-19. Symptoms at disease onset tend to aggregate differently by age. New diagnostic algorithms considering age and chronic conditions may ease Covid-19 diagnosis and optimize health resources allocation.

TRIAL REGISTRATION

NCT04471701 (ClinicalTrials.gov).

Olfactory language and semantic processing in anosmia: a neuropsychological case control study

A longstanding debate within philosophy and neuroscience involves the extent to which sensory information is a necessary condition for conceptual knowledge. Much of our understanding of this relationship has been informed by examining the impact of congenital blindness and deafness on language and cognitive development. Relatively little is known about the "lesser" senses of smell and taste. Here we report a neuropsychological case-control study contrasting a young adult male (P01) diagnosed with anosmia (i.e. no olfaction) during early childhood relative to an age- and sex-matched control group. A structural MRI of P01's brain revealed profoundly atrophic/aplastic olfactory bulbs, and standardized smell testing confirmed his prior pediatric diagnosis of anosmia. Participants completed three language experiments examining comprehension, production, and subjective experiential ratings of odor salient words (e.g. sewer) and scenarios (e.g. fish market). P01's ratings of odor salience of single words were lower than all control participants, whereas his ratings on five other perceptual and affective dimensions were similar to controls. P01 produced unusual associations when cued to generate words that smelled similar to odor-neutral target words (e.g. ink → plant). In narrative picture description for odor salient scenes (e.g. bakery), P01 was indistinguishable from controls. These results suggest that odor deprivation does not overtly impair functional language use. However, subtle lexical-semantic effects of anosmia may be revealed using sensitive linguistic measures.

Clinical Olfactory Working Group consensus statement on the treatment of postinfectious olfactory dysfunction

BACKGROUND

Respiratory tract viruses are the second most common cause of olfactory dysfunction. As we learn more about the effects of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), with the recognition that olfactory dysfunction is a key symptom of this disease process, there is a greater need than ever for evidence-based management of postinfectious olfactory dysfunction (PIOD).

OBJECTIVE

Our aim was to provide an evidence-based practical guide to the management of PIOD (including post-coronavirus 2019 cases) for both primary care practitioners and hospital specialists.

METHODS

A systematic review of the treatment options available for the management of PIOD was performed. The written systematic review was then circulated among the members of the Clinical Olfactory Working Group for their perusal before roundtable expert discussion of the treatment options. The group also undertook a survey to determine their current clinical practice with regard to treatment of PIOD.

RESULTS

The search resulted in 467 citations, of which 107 articles were fully reviewed and analyzed for eligibility; 40 citations fulfilled the inclusion criteria, 11 of which were randomized controlled trials. In total, 15 of the articles specifically looked at PIOD whereas the other 25 included other etiologies for olfactory dysfunction.

CONCLUSIONS

The Clinical Olfactory Working Group members made an overwhelming recommendation for olfactory training; none recommended monocycline antibiotics. The diagnostic role of oral steroids was discussed; some group members were in favor of vitamin A drops. Further research is needed to confirm the place of other therapeutic options.

Could Early Identification of Changes in Olfactory Function Be an Indicator of Preclinical Neurodegenerative Disease? A Systematic Review

INTRODUCTION

Alzheimer's disease (AD) is a debilitating neurodegenerative disease that currently affects 850,000 individuals in the UK with estimates continuing to rise. Diagnosis is only available in the presence of significant neuronal pathology and apparent cognitive decline, meaning that treatment avenues are often limited and carry little to no effect on prognosis. Olfactory function has been shown to have a direct correlation with cognitive function and therefore may serve as a potential diagnostic tool for the detection of preclinical disease. The objective was to examine the current literature to establish the accuracy of olfactory function testing in determining current and future cognitive function.

METHODS

A systematic review was performed via Medline on 17 October 2019 using the search terms and Boolean operators 'Dementia OR Alzheimer's AND olfaction AND cognitive impairment' yielding 111 results. These were then screened using inclusion/exclusion criteria alongside a PICO strategy. After titles, abstracts and full text were screened, nine articles were included in the review and critically appraised using the AXIS and CASP tools.

RESULTS

Significant correlations are demonstrated between olfactory impairment (OI) and cognitive decline. However, there were limitations of many of the studies in that confounders such as head trauma, upper respiratory infection (URTI) and smoking history were not considered. The majority of the studies also used an olfactory screening tool that was not designed for the population being examined.

CONCLUSION

Despite improvements in olfactory testing needing to be implemented, OI is clearly impaired in neurodegenerative disease across a multitude of ages and cultures, offering an early marker of future cognitive decline. As a result of the heterogenous nature of the included studies, there is a further need for future research to ensure the sensitivity, validity and reliability of implementing olfactory testing as an early marker of future cognitive decline.

A Prospective Study on Risk Factors for Olfactory Dysfunction in Aging

Background

Olfactory dysfunction (OD) refers to a reduced or absent ability to smell. OD negatively impacts health and quality of life and its prevalence increases with advancing age. Since OD may be an early marker of dementia and impending death, more knowledge regarding risk factors of OD in aging is warranted. The objective was therefore to explore longitudinally which demographic, genetic, clinical, lifestyle, and cognitive factors predict the development of OD.

Methods

The study included participants aged 60–90 years from the Swedish National Study on Aging and Care in Kungsholmen (SNAC-K), who did not have OD at baseline and were reassessed with an odor identification task at a 6-year follow-up (n = 1,004). Risk factors of OD were assessed with multivariable logistic regression analyses.

Results

The percentage of incident OD cases was 14.2% over 6 years in the total sample and this number increased monotonically with age. Increasing age, carrying the ε4 allele of the APOE gene, atrial fibrillation, cerebrovascular disease, and current smoking were found to be risk factors for the development of OD, whereas better olfactory identification and verbal episodic memory proficiency at baseline were identified as protective factors.

Conclusions

In addition to nonmodifiable factors (age and genetic risk), several modifiable risk factors of OD were identified. This suggests that it might be possible to reduce OD incidence through the management of vascular risk factors and maintenance of a healthy lifestyle.

Loss of Olfactory Function-Early Indicator for Covid-19, Other Viral Infections and Neurodegenerative Disorders

The loss of the senses of smell (anosmia) and taste (ageusia) are rather common disorders, affecting up to 20% of the adult population. Yet, this condition has not received the attention it deserves, most probably because per se such a disorder is not life threatening. However, loss of olfactory function significantly reduces the quality of life of the affected patients, leading to dislike in food and insufficient, exaggerated or unbalanced food intake, unintentional exposure to toxins such as household gas, social isolation, depression, and an overall insecurity. Not only is olfactory dysfunction rather prevalent in the healthy population, it is, in many instances, also a correlate or an early indicator of a panoply of diseases. Importantly, olfactory dysfunction is linked to the two most prominent neurodegenerative disorders, Parkinson's disease and Alzheimer's disease. Anosmia and hyposmia (reduced sense of smell) affect a majority of patients years before the onset of cognitive or motor symptoms, establishing olfactory dysfunction as early biomarker that can enable earlier diagnosis and preventative treatments. In the current health crisis caused by SARS-CoV2, anosmia and dysgeusia as early-onset symptoms in virus-positive patients may prove to be highly relevant and crucial for pre-symptomatic Covid-19 detection from a public health perspective, preceding by days the more classical respiratory tract symptoms such as cough, tightness of the chest or fever. Thus, the olfactory system seems to be at the frontline of pathologic assault, be it through pathogens or insults that can lead to or at least associate with neurodegeneration. The aim of this review is to assemble current knowledge from different medical fields that all share a common denominator, olfactory/gustatory dysfunction, and to distill overarching etiologies and disease progression mechanisms.

The olfactory deficits of depressed patients are restored after remission with venlafaxine treatment

BACKGROUND

It is unclear whether olfactory deficits improve after remission in depressed patients. Therefore, we aimed to assess in drug-free patients the olfactory performance of patients with major depressive episodes (MDE) and its change after antidepressant treatment.

METHODS

In the DEP-ARREST-CLIN study, 69 drug-free patients with a current MDE in the context of major depressive disorder (MDD) were assessed for their olfactory performances and depression severity, before and after 1 (M1) and 3 (M3) months of venlafaxine antidepressant treatment. They were compared to 32 age- and sex-matched healthy controls (HCs). Olfaction was assessed with a psychophysical test, the Sniffin' Sticks test (Threshold: T score; Discrimination: D score; Identification: I score; total score: T + D + I = TDI score) and Pleasantness (pleasantness score: p score; neutral score: N score; unpleasantness score: U score).

RESULTS

As compared to HCs, depressed patients had lower TDI olfactory scores [mean (s.d.) 30.0(4.5) v. 33.3(4.2), p < 0.001], T scores [5.6(2.6) v. 7.4(2.6), p < 0.01], p scores [7.5(3.0) v. 9.8(2.8), p < 0.001)] and higher N scores [3.5(2.6) v. 2.1(1.8), p < 0.01]. T, p and N scores at baseline were independent from depression and anhedonia severity. After venlafaxine treatment, significant increases of T scores [M1: 7.0(2.6) and M3: 6.8(3.1), p < 0.01] and p scores [M1: 8.1(3.0) and M3: 8.4(3.3), p < 0.05] were evidenced, in remitters only (T: p < 0.01; P: p < 0.01). Olfaction improvement was mediated by depression improvement.

CONCLUSIONS

The olfactory signature of MDE is restored after venlafaxine treatment. This olfaction improvement is mediated by depression improvement.

Hedonicity in functional motor disorders: a chemosensory study assessing taste

The aim of this study was to explore hedonicity to basic tastes in patients with functional motor disorders (FMDs) that are often associated with impairment in emotional processing. We recruited 20 FMD patients and 24 healthy subjects, matched for age and sex. Subjects were asked to rate the hedonic sensation (i.e., pleasant, neutral, and unpleasant) on a - 10 to +10 scale to the four basic tastes (sweet, sour, salty, and bitter) at different concentrations, and neutral stimuli (i.e., no taste stimulation) by means of the Taste Strips Test. Anxiety, depression, and alexithymia were assessed. FMD patients rated the highest concentration of sweet taste (6.7 ± 2.6) as significantly more pleasant than controls (4.7 ± 2.5, p = 0.03), and the neutral stimuli significantly more unpleasant (patients: - 0.7 ± 0.4, controls: 0.1 ± 0.4, p = 0.013). Hedonic ratings were not correlated to anxiety, depression, or alexithymia scores. Hedonic response to taste is altered in FMD patients. This preliminary finding might result from abnormal interaction between sensory processing and emotional valence.

Epigenome-450K-wide methylation signatures of active cigarette smoking: The Young Finns Study

Smoking as a major risk factor for morbidity affects numerous regulatory systems of the human body including DNA methylation. Most of the previous studies with genome-wide methylation data are based on conventional association analysis and earliest threshold-based gene set analysis that lacks sensitivity to be able to reveal all the relevant effects of smoking. The aim of the present study was to investigate the impact of active smoking on DNA methylation at three biological levels: 5'-C-phosphate-G-3' (CpG) sites, genes and functionally related genes (gene sets). Gene set analysis was done with mGSZ, a modern threshold-free method previously developed by us that utilizes all the genes in the experiment and their differential methylation scores. Application of such method in DNA methylation study is novel. Epigenome-wide methylation levels were profiled from Young Finns Study (YFS) participants' whole blood from 2011 follow-up using Illumina Infinium HumanMethylation450 BeadChips. We identified three novel smoking related CpG sites and replicated 57 of the previously identified ones. We found that smoking is associated with hypomethylation in shore (genomic regions 0-2 kilobases from CpG island). We identified smoking related methylation changes in 13 gene sets with false discovery rate (FDR) ≤ 0.05, among which is olfactory receptor activity, the flagship novel finding of the present study. Overall, we extended the current knowledge by identifying: (i) three novel smoking related CpG sites, (ii) similar effects as aging on average methylation in shore, and (iii) a novel finding that olfactory receptor activity pathway responds to tobacco smoke and toxin exposure through epigenetic mechanisms.

Age-Related Olfactory Dysfunction: Epidemiology, Pathophysiology, and Clinical Management

Like other sensory systems, olfactory function deteriorates with age. Epidemiological studies have revealed that the incidence of olfactory dysfunction increases at the age of 60 and older and males are more affected than females. Moreover, smoking, heavy alcohol use, sinonasal diseases, and Down’s syndrome are associated with an increased incidence of olfactory dysfunction. Although the pathophysiology of olfactory dysfunction in humans remains largely unknown, studies in laboratory animals have demonstrated that both the peripheral and central olfactory nervous systems are affected by aging. Aged olfactory neuroepithelium in the nasal cavity shows the loss of mature olfactory neurons, replacement of olfactory neuroepithelium by respiratory epithelium, and a decrease in basal cell proliferation both in the normal state and after injury. In the central olfactory pathway, a decrease in the turnover of interneurons in the olfactory bulb (OB) and reduced activity in the olfactory cortex under olfactory stimulation is observed. Recently, the association between olfactory impairment and neurodegenerative diseases, such as Alzheimer’s disease (AD) and Parkinson’s disease (PD), has gained attention. Evidence-based pharmacotherapy to suppress or improve age-related olfactory dysfunction has not yet been established, but preliminary results suggest that olfactory training using odorants may be useful to improve some aspects of age-related olfactory impairment.

Chronic Cigarette Smoking Associates Directly and Indirectly with Self-Reported Olfactory Alterations: Analysis of the 2011-2014 National Health and Nutrition Examination Survey

INTRODUCTION

Population-based studies show inconsistent effects of cigarette smoking on olfactory function. We aimed to identify direct and indirect associations between measures of smoking exposure/nicotine dependence and altered olfaction in a nationally representative sample of adults.

METHODS

NHANES 2011-2014 (n = 7418) participants (mean age = 57.8 ± 12.2 years) self-reported olfaction and related health and demographic risks. Affirmative answers to three questions defined altered olfaction (olfactory problems in the past years; worse ability since age 25; phantom smells). Smoking (never, former, current) was self-reported by chronicity (pack years, PY) and dependency (time to first cigarette upon waking) and verified by serum cotinine. Associations were tested with logistic regression, reporting odds ratios (ORs) and 95% confidence intervals (CIs), and mediation models.

RESULTS

Estimated prevalence of altered olfaction was 22.3%, with age-related increases. Nearly half of the sample were former/current smokers (47.4%). Controlling for olfactory-related risks, ≥10 PY smokers had significantly greater odds of altered olfaction versus never smokers (OR 1.36, CI: 1.06-1.74). The odds of altered olfaction were heightened among current smokers (≥10 PY) who also had high nicotine dependence (smoked ≤30 min of waking) (OR 1.41, CI: 1.01-1.99). Light smokers (≤10 PY smokers) did not show increased odds versus never smokers. Current smokers who also were heavy drinkers (≥4 drinks/day) had the highest odds for altered olfaction (OR 1.96, CI: 1.20-3.19). Olfactory-related pathologies (sinonasal problems, serious head injury, tonsillectomy, xerostomia) partially mediated the association between smoking and altered olfaction.

CONCLUSIONS

Chronic cigarette smoking was associated with increased odds of self-reported olfactory alterations, directly and indirectly via olfactory-related pathologies.

IMPLICATIONS

Analysis of the US nationally representative data revealed significant positive associations between chronic smoking and alterations in the sense of smell. Rates of smell alteration (self-reported problems in the past year, losses with aging, and phantom smells) increased from 23% among adults to 33% for chronic smokers and 38% for chronic smokers who also reported heavy drinking. Chronic smoking showed associations with smell alteration that were direct and indirect through exposure to olfactory-related pathologies (naso-sinus problems, dry mouth, head/facial injury). Smell alteration can impact smokers' quality of life by challenging the ability to sense warning odors, food flavor, and olfactory-stimulated emotions and memories.

The Association Between Smoking on Olfactory Dysfunction in 3,900 Patients With Olfactory Loss

OBJECTIVES/HYPOTHESIS

The association between smoking and olfactory loss remains a conundrum. Prior studies have found negative and positive effects of smoking on olfactory function in the general population. However, smoking cessation seems to improve both rated and measured olfactory function. The purpose of this study was to investigate the olfactory function and smoking habits in patients with olfactory loss caused by different etiologies to unveil underlying patterns related to smoking.

STUDY DESIGN

Retrospective observational study.

METHODS

Patients were included from two specialized taste and smell centers. Patients underwent olfactory testing, clinical examination including rhinoscopy, and the underlying etiology was identified. Patterns of olfactory test scores, demographics, and etiologies were analyzed.

RESULTS

In total, 3,900 patients with olfactory loss were included. Of these, 521 were current smokers, and 316 were former smokers. Patients with a history of smoking did not have significantly lower olfactory function. Current smokers were more often affected by posttraumatic olfactory loss, but not sinonasal, postviral, or idiopathic olfactory loss.

CONCLUSIONS

Current smoking, but not former smoking, was associated with posttraumatic olfactory loss. In relation to measured olfactory function, a history of smoking was not associated to lower olfactory scores. Our findings suggest that the general recommendations of smoking cessation for patients with olfactory loss are especially relevant for patients with posttraumatic olfactory loss. The nature of this association between current smoking and posttraumatic olfactory loss has yet to be elucidated.

LEVEL OF EVIDENCE

2b Laryngoscope, 131:E8-E13, 2021.

Factors associated with odour identification in older Indonesian and white Australian adults

BACKGROUND AND AIMS

Among older adults, olfactory dysfunction is associated with cognitive impairment, lower quality of life, and increased mortality. While age is a risk factor for olfactory dysfunction, other risk factors are less well understood, and may vary between ethno-regional groups. This study investigated how associations between odour identification (OI) and various risk factors, as well as cognition and language ability, differed or were similar in two distinct ethno-regional groups of older adults.

METHODS

This cross-sectional study used data from two cohorts: 470 Indonesians (aged 67.4 ± 7.4 years) and 819 white Australians (aged 78.7 ± 4.8 years). Univariate and multivariate analyses explored whether OI test scores were associated with age, sex, education, cholesterol levels, apolipoprotein E ε4 status, smoking, diabetes, hypertension and depression scale scores, or with Mini-Mental State Examination (MMSE) and language test performance.

RESULTS

Univariate analyses identified some factors associated with OI scores in both Indonesians and white Australians, including older age and smoking with lower scores, and MMSE and language test performance with higher scores. Multivariate analyses yielded different and mutually exclusive patterns of associations in the two ethno-regional groups, with language test scores significantly associated with higher OI scores in Indonesians, and age, being male, smoking, having diabetes and higher depression scale scores significantly associated with lower OI scores in white Australians.

CONCLUSION

Ethno-regional differences may need consideration in the attempt to fully understand associations between OI and negative outcomes like dementia and mortality, and interventions for olfactory dysfunction might need to be tailored to specific ethno-regional groups. However, the difference in mean age between cohorts is a limitation of this study, and future studies should aim to compare populations with similar age distributions.

The Changing Landscape of Parkinson Epidemiologic Research

Despite recent successes in understanding the genetics of Parkinson’s disease (PD), the causes of late-onset sporadic PD remain elusive. Many of the epidemiologic findings on PD etiology have been challenged by alternative explanations such as reverse causation. This is mainly because PD often takes decades to develop before it can be diagnosed late in life. Convincing evidence shows that this prodromal stage of PD is characterized by various prodromal symptoms such as olfactory impairment and rapid-eye-movement sleep behavior disorder (RBD). As they likely reflect PD pathogenesis years, if not decades, before nigrostriatal involvement, research on these symptoms may represent an unprecedented opportunity to dissect the etiology of PD. Using PD prodromal symptoms as intermediate phenotypes, we may be able to identify factors that contribute to the development of these symptoms and factors that modify their progression to clinical PD. Further, this line of research will also enable examinations of novel etiological hypotheses of PD development such as the microbiome and prion hypotheses. In this article, the author used olfactory impairment and RBD as examples to illustrate the promises and challenges of epidemiologic research on prodromal symptoms to understand PD etiology.

Factors Associated With Phantom Odor Perception Among US Adults: Findings From the National Health and Nutrition Examination Survey

Importance

Phantom odor perception can be a debilitating condition. Factors associated with phantom odor perception have not been reported using population-based epidemiologic data.

Objective

To estimate the prevalence of phantom odor perception among US adults 40 years and older and identify factors associated with this condition.

Design, Setting, and Participants

In this cross-sectional study with complex sampling design, 7417 adults 40 years and older made up a nationally representative sample from data collected in 2011 through 2014 as part of the National Health and Nutrition Examination Survey.

Exposures

Sociodemographic characteristics, cigarette and alcohol use, head injury, persistent dry mouth, smell function, and general health status.

Main Outcomes and Measures

Phantom odor perception ascertained as report of unpleasant, bad, or burning odor when no actual odor exists.

Results

Of the 7417 participants in the study, 52.8% (3862) were women, the mean (SD) age was 58 (12) years, and the prevalence of phantom odor perception occurred in 534 participants, which was 6.5% of the population (95% CI, 5.7%-7.5%). Phantom odor prevalence varied considerably by age and sex. Women 60 years and older reported phantom odors less commonly (7.5% [n = 935] and 5.5% [n = 937] among women aged 60-69 years and 70 years and older, respectively) than younger women (9.6% [n = 1028] and 10.1% [n = 962] among those aged 40-49 years and 50-59 years, respectively). The prevalence among men varied from 2.5% (n = 846) among men 70 years and older to 5.3% (n = 913) among men 60 to 69 years old. Phantom odor perception was 60% (n = 1602) to 65% (n = 2521) more likely among those with an income-to-poverty ratio of less than 3 compared with those in the highest income-to-poverty ratio group (odds ratio [OR], 1.65; 95% CI, 1.06-2.56; and OR, 1.60; 95% CI, 1.01-2.54 for income-to-poverty ratio <1.5 and 1.5-2.9, respectively). Health conditions associated with phantom odor perception included persistent dry mouth (OR, 3.03; 95% CI, 2.17-4.24) and history of head injury (OR, 1.74; 95% CI, 1.20-2.51).

Conclusions and Relevance

An age-related decline in the prevalence of phantom odor perception is observed in women but not in men. Only 11% (n = 64) of people who report phantom odor perception have discussed a taste or smell problem with a clinician. Associations of phantom odor perception with poorer health and persistent dry mouth point to medication use as a potential explanation. Prevention of serious head injuries could have the added benefit of reducing phantom odor perception.

Olfactory dysfunction persists after smoking cessation and signals increased cardiovascular risk

BACKGROUND

Olfaction plays a critical role in health and function in older adults, and impaired sense of smell is a strong predictor of morbidity and mortality. Smoking cigarettes causes olfactory impairment, but the mechanism of damage and ability to recover after cessation are unknown. We investigated the relationship between time since quitting and olfactory dysfunction in order to elucidate the mechanism(s) by which smoking damages the olfactory system and to inform patient counseling.

METHODS

Using longitudinal data from the National Social Life Health and Aging Project (n = 3528 older adults, including 1526 former smokers), we analyzed the association between odor identification performance and time since smoking cessation using multivariate ordinal logistic regression, adjusting for cognition and demographic variables. To test whether vascular disease plays a role, we also assessed the relationship between olfactory decline and incidence of heart attack and heart disease.

RESULTS

Former smokers who quit ≤15 years before testing had significantly impaired olfaction compared to never smokers (p = 0.04), but those who quit >15 years prior did not. Olfactory decline over 5 years showed modest evidence toward predicting increased incidence of heart attack or heart disease (p = 0.08).

CONCLUSION

Olfactory impairment in smokers persists 15 years after quitting, which is consistent with a vascular mechanism of impairment. Indeed, olfactory decline is a predictor of the development of cardiovascular disease. Taken together, these data suggest that olfactory loss may be a useful sign of underlying vascular pathology. Further investigation of olfactory loss as an early biomarker for cardiovascular disease is warranted.

Parkinsonism Relating to Intoxication with Glyphosate

We herein report the case of a 38-year-old man who developed parkinsonism 4 years after ingesting glyphosate. The patient presented with right-sided bradykinesia and cogwheel rigidity without autonomic symptoms. Magnetic resonance imaging of the brain and [123I]-metaiodobenzylguanidine myocardial scintigraphy were normal. A drastic response to levodopa and the presence of levodopa-induced dyskinesia without strong non-motor symptoms were seen in this patient. We considered that young-onset atypical parkinsonism was associated with a history of sublethal glyphosate ingestion. Epidemiologic investigations have shown that exposure to pesticides is a risk factor for Parkinson's disease (PD). Our findings support the notion that glyphosate exposure might be related to the onset of PD.

Olfactory impairment in frontotemporal dementia: A systematic review and meta-analysis

Frontotemporal dementia (FTD) presents clinically in three variants: one behavioral and two with progressive primary aphasia - non-fluent/agrammatic and semantic. Defined by the degenerative process and cerebral atrophy, olfactory dysfunction occurs in up to 96% of previous FTD case series.

Objective

the present study aims to critically synthesize data about the relationship between FTD and olfactory impairment to analyze the usefulness of olfactory evaluation tests as a complementary element in early diagnosis.

Methods

a database search was performed using the keywords "olfactory OR smell OR olfaction AND frontotemporal dementia". We included studies that evaluated olfactory function in patients diagnosed with frontotemporal dementia, all subtypes, compared with age-matched healthy controls. For comparative purposes, the effect size was calculated using Cohen's D. The studies selected were categorized according to dementia variant and olfactory test type. A meta-analysis was performed using forest plots - homogeneity was evaluated by statistical tests (i² and Cochran Q).

Results

ten articles met the inclusion criteria. Heterogeneity was classified as low for semantic dementia olfactory identification and behavioral variant olfactory discrimination groups (i² = 0 and 3.4%, respectively) and as moderate for the behavioral variant olfactory identification group (i² = 32.6%).

Conclusion

patients with the frontotemporal dementia behavioral variant seem to present with alterations in odor identification, but with preserved discrimination. Scent identification also seems to be impaired in semantic dementia. Therefore, we conclude that olfactory evaluation in these patients is possibly impacted by cognitive alterations and not by sensory deficits. Application of olfactory tests may prove important in differentiating prodromal states from other types of dementia with more pronounced olfactory impairment.

Perceived health effects of vaping among Hungarian adult e-cigarette-only and dual users: a cross-sectional internet survey

BACKGROUND

Knowledge about the health effects of e-cigarette use (or vaping) among past and current combustible cigarette users is limited. Several studies have assessed vaping-related adverse events (AEs) and beneficial health effects, however, most studies focused on AEs in general and examined only a few physiological changes that vapers experience. This study aims to explore self-reported AEs and perceived health changes due to e-cigarette use among Hungarian adult e-cigarette-only users (former smokers who switched completely to e-cigarette use) and dual users (smokers who use e-cigarettes and combustible tobacco cigarettes concomitantly).

METHODS

A cross-sectional, web-based survey of 1042 adult Hungarian e-cigarette users was conducted in 2015. Participants reported AEs and changes in physiological functions since they switched from smoking to e-cigarette use or while dually using e-cigarettes and combustible cigarettes. Confirmatory factor analysis with covariates was applied to explain perceived health changes due to e-cigarette-only use and dual use.

RESULTS

Dual users (17.6%) were significantly more likely to report AEs of vaping than e-cigarette-only users (26.2% vs. 11.8%, p < 0.001). Experiencing health improvements were significantly more likely among e-cigarette-only users than for dual users for all surveyed physiological functions. E-cigarette-only users reported larger effects of vaping on sensory, physical functioning, and mental health factors compared to dual users. Self-reported changes in sensory and physical functioning were significantly higher among individuals using e-cigarettes more than a year and people who were past heavy smokers (smoked ≥20 cigarettes per day). Gender was related to sensory improvement only; males reported greater improvement than females.

CONCLUSIONS

The majority of e-cigarette-only users reported more perceived beneficial changes in physiological functions and fewer AEs than dual users. Perceived short-term benefits of e-cigarette use may reinforce users despite the uncertainty of long-term health consequences. Health professionals should provide balanced information regarding the possible short- and long-term positive and negative health effects of e-cigarette use during consultations with patients.

Modeling Associations between Chemosensation, Liking for Fats and Sweets, Dietary Behaviors and Body Mass Index in Chronic Smokers

Chronic smokers have a greater risk for altered chemosensation, unhealthy dietary patterns, and excessive adiposity. In an observational study of chronic smokers, we modeled relationships between chemosensation, fat/carbohydrate liking, smoking-associated dietary behaviors, and body mass index (BMI). Also tested in the model was liking for sweet electronic cigarette juice (e-juice). Smokers (n = 135, 37 ± 11 years) were measured for: Taste genetics (intensity of 6-n-propylthiouracil-PROP); taste (NaCl and quinine intensities) and olfactory (odor identification) function; liking for cherry e-juice; and weight/height to calculate BMI. Smokers survey-reported their food liking and use of smoking for appetite/weight control. Structural equation models tested direct and indirect relationships between chemosensation, fat/carbohydrate liking, dietary behaviors, and BMI. In good-fitting models, taste intensity was linked to BMI variation through fat/carbohydrate liking (greater PROP intensity→greater NaCl intensity→greater food liking→higher BMI). Olfactory function tended to predict sweet e-juice liking, which, in turn, partially mediated the food liking and BMI association. The path between smoking-associated dietary behaviors and BMI was direct and independent of chemosensation or liking. These findings indicate that taste associates with BMI in chronic smokers through liking of fats/carbohydrates. Future research should determine if vaping sweet e-juice could improve diet quality and adiposity for smokers.

High Pesticide Exposure Events and Olfactory Impairment among U.S. Farmers

BACKGROUND

Olfactory impairment (OI) is common among older adults and independently predicts all-cause mortality and the risk of several major neurodegenerative diseases. Pesticide exposure may impair olfaction, but empirical evidence is lacking.

OBJECTIVE

We aimed to examine high pesticide exposure events (HPEEs) in relation to self-reported OI in participants in the Agricultural Health Study (AHS).

METHODS

We conducted multivariable logistic regression to examine the associations between HPEEs reported at enrollment (1993–1997) and self-reported OI at the latest AHS follow-up (2013–2015) among 11,232 farmers, using farmers without HPEEs as the reference or unexposed group.

RESULTS

A total of 1,186 (10.6%) farmers reported OI. A history of HPEEs reported at enrollment was associated with a higher likelihood of reporting OI two decades later {odds ratio [Formula: see text] [95% confidence interval (CI): 1.28, 1.73]}. In the analyses on the HPEE involving the highest exposure, the association appears to be stronger when there was a [Formula: see text] delay between HPEE and washing with soap and water [e.g., [Formula: see text] (95% CI: 1.48, 2.89) for 4-6 h vs. [Formula: see text] (95% CI: 1.11, 1.75) for [Formula: see text]]. Further, significant associations were observed both for HPEEs involving the respiratory or digestive tract [[Formula: see text] (95% CI: 1.22, 1.92)] and dermal contact [[Formula: see text] (95% CI: 1.22, 1.78)]. Finally, we found significant associations with several specific pesticides involved in the highest exposed HPEEs, including two organochlorine insecticides (DDT and lindane) and four herbicides (alachlor, metolachlor, 2,4-D, and pendimethalin). HPEEs that occurred after enrollment were also associated with OI development.

CONCLUSIONS

HPEEs may cause long-lasting olfactory deficit. Future studies should confirm these findings with objectively assessed OI and also investigate potential mechanisms. https://doi.org/10.1289/EHP3713.

Management and outcomes of pregnancy with or without lupus nephritis: a systematic review and meta-analysis

Background

Although it is well established that systemic lupus erythematosus (SLE) negatively affects pregnancy outcomes, there is insufficient evidence on the effect of lupus nephritis (LN) on antenatal management and pregnancy outcomes. We performed a systematic review and meta-analysis to determine the association of LN with management and pregnancy outcomes in SLE patients.

Methods

Embase, Medline, Cochrane, and ClinicalTrials.gov were carefully searched for relevant English and Chinese language studies. A total of 2,987 articles were reviewed. Data were extracted that compared management and pregnancy outcomes in SLE pregnant women with LN vs without LN. Risk of bias was assessed by a modified version of the Newcastle-Ottawa Scale and the STROBE checklist. Combined odds ratios (OR) and 95% confidence intervals (CI) were obtained and sensitivity analysis was performed using RevMan 5.3 software.

Results

Sixteen studies, including 1,760 pregnant patients with SLE, were included. Gestational hypertension (OR=5.65, 95% CI=2.94–10.84), preeclampsia (OR=2.84, 95% CI=1.87–4.30), SLE flare (OR=2.66, 95% CI=1.51–4.70), renal flare (OR=15.18, 95% CI=5.89–39.14), proteinuria (OR=8.86, 95% CI=4.75–16.52), and hypocomplementemia (OR=2.86, 95% CI=1.68–4.87) were significantly affected in pregnant women with LN. Anti-Sjögren’s syndrome-related antigen A/Ro autoantibodies were negatively associated with pregnant women with LN (OR=0.57, 95% CI=0.33–0.98). Pregnant women with LN presented a significant decrease in live births (OR=0.62, 95% CI=0.49–0.80) and a significant increase in preterm births (OR=1.92, 95% CI=1.49–2.49) and fetal growth restriction (OR=1.43, 95% CI=1.08–1.91). Regarding antenatal management, steroids (OR=2.48, 95% CI=1.59–3.87) and immunosuppressant treatment (OR=6.77, 95% CI=3.30–13.89) were more frequently used in women with LN.

Conclusion

This review identified a significant association between the aforementioned outcomes and SLE pregnant patients with LN. In patients with SLE, LN increased the risks for adverse pregnancy outcomes and the use of medication. Therefore, special treatment and close monitoring should be allocated to pregnant women with LN.

Causality Assessment of Olfactory and Gustatory Dysfunction Associated with Intranasal Fluticasone Propionate: Application of the Bradford Hill Criteria

Causality assessment is crucial to post-marketing pharmacovigilance and helps optimize safe and appropriate use of medicines by patients in the real world. Self-reported olfactory and gustatory dysfunction are common in the general population as well as in patients with allergic rhinitis and nasal polyposis. Intranasal corticosteroids, including intranasal fluticasone propionate (INFP), are amongst the most effective drugs indicated in the treatment of allergic rhinitis and nasal polyposis. While intranasal corticosteroids are associated with olfactory and gustatory dysfunction and are currently labeled for these adverse events, causality assessment has not been performed to date. Although there is no single widely accepted method to assess causality in pharmacovigilance, the Bradford Hill criteria offer a robust and comprehensive approach because nine distinct aspects of an observed potential drug–event association are assessed. In this literature-based narrative review, Hill’s criteria were applied to determine causal inference between INFP and olfactory and gustatory dysfunction.

Factors Influencing the Phenotypic Characterization of the Oral Marker, PROP

In the last several decades, the genetic ability to taste the bitter compound, 6-n-propyltiouracil (PROP) has attracted considerable attention as a model for understanding individual differences in taste perception, and as an oral marker for food preferences and eating behavior that ultimately impacts nutritional status and health. However, some studies do not support this role. This review describes common factors that can influence the characterization of this phenotype including: (1) changes in taste sensitivity with increasing age; (2) gender differences in taste perception; and (3) effects of smoking and obesity. We suggest that attention to these factors during PROP screening could strengthen the associations between this phenotype and a variety of health outcomes ranging from variation in body composition to oral health and cancer risk.