The association between diabetes and olfactory impairment in adults: A systematic review and meta-analysis

Association of nasal surgery with olfactory function among older adults

BACKGROUND/PURPOSE

Olfactory Dysfunction (OD) is a prevalent condition that commonly presents in the older adult population. Various factors have been shown to contribute to OD, such as neurodegenerative disease, older age, and smoking status; however, the influence of nasal surgery on olfactory function is not well delineated. This study seeks to explore the potential effect of nose surgery on olfactory function.

METHODS

This cross-sectional study was conducted on data for 2285 adults from Round 1 of the National Social Life, Health, and Aging Project (NSHAP), a nationally representative sample of US older adults. The 5-item Sniffin' Sticks test was used to define olfactory function: correctly identifying ≥4 odors indicated normal olfactory function, while correctly identifying 0-3 odors was considered OD Associations between prior nasal surgery and OD were assessed using multivariable logistic regression, and adjusted odds ratios (OR) were calculated. Analyses were weighted using NSHAP-provided person-level weights to account for sampling design.

RESULTS

OD was present in 18.4 % of adults. The weighted average age was 67.1 ± 7.2 years among those with normal olfaction and 70.9 ± 7.9 years for those with OD. Of adults with OD, 9.8 % had a prior nasal surgery as compared to 8.1 % of those with normal olfaction, although the difference was not statistically significant. After adjusting for age, gender, race, education, prior stroke, dementia, and self-reported mental health, prior nasal surgery was not significantly associated with OD (OR: 1.14; 95 % CI: 0.77-1.70).

CONCLUSION

Prior nasal surgery was not associated with OD after controlling for covariates. While this study does provide unique insight into the relationship between nasal surgery and OD in nationally representative cohort of older adults, it was limited since the dataset utilized did not contain information on the specific surgery that participants underwent. Therefore, further research with more detailed information on the types of nasal surgeries and sinonasal conditions prior to surgery would further help elucidate the relationship between and nasal surgery and OD.

Association between subtypes of diabetes and special sensations: A 2-sample Mendelian randomization study

Diabetes, a chronic condition affecting millions of individuals, is divided into type 1 diabetes (T1D) and type 2 diabetes (T2D), each with unique pathophysiological characteristics. While the impact of diabetes on vision is established, its relationship with other special senses, balance, hearing, and olfaction, remains uncertain. This study utilized a 2-sample Mendelian randomization (MR) approach to investigate the associations between diabetes subtypes and specific sensory disorders. We performed MR analysis using various methods (inverse variance weighting [IVW], MR-Egger, simple mode, weighted mode, weighted median, MR-PRESSO) to assess the causal relationships between diabetes subtypes and sensory disorders (vestibular dysfunction, sensorineural hearing loss, conductive hearing loss, and olfactory dysfunction). Different diabetes genome-wide association studies datasets were utilized for validation. MR analysis revealed no significant correlations between T1D or T2D and the sensory disorders studied. Interestingly, an initial signal suggested that T1D might increase the risk of conductive hearing loss (IVW: odds ratio = 1.120, 95% CI: 1.035-1.211, P = .005), but this finding was not supported by validation studies. No evidence of horizontal pleiotropy or heterogeneity was found (P > .05). Our MR analysis and subsequent validation revealed no significant associations between diabetes subtypes and special senses. The initial suggestion of an increased risk of conductive hearing loss in T1D patients was not confirmed. Future research should further explore the intricate relationships among diabetes, sensory functions, and other factors, as well as the potential effects of diabetes management on sensory health.

Olfactory Dysfunction as a Biomarker for Early Diagnosis of Cognitive Impairment in Patients With Type 2 Diabetes: A Systematic Review

Background: Olfactory dysfunction and cognitive impairment (CI) have been associated with Type 2 diabetes (T2DM), but the mechanisms underlying this association are broadly unknown. This systematic review tends to investigate the relationship between the onset of olfactory dysfunction and CI in patients with T2DM and to explore the potential role of olfactory dysfunction as an early diagnosis biomarker of CI. Methods: We conducted a systematic review consulting PubMed and Scopus. The articles considered eligible included patients with T2DM and cognitive and olfactory test. Results: The search identified a total of 145 articles, of which 13 were finally selected. The majority of these studies discovered a correlation between olfactory dysfunction and CI in individuals with T2DM. Additionally, other biomarkers such as functional magnetic resonance imaging demonstrated changes in brain regions associated with the sense of smell in T2DM patients. Conclusions: Olfactory dysfunction could be a biomarker for early diagnosis of CI in T2DM. However, these alterations are highly heterogeneous and more studies that include neuroimaging need to be conducted.

Diabetic Neuropathy Is Related to Rhinencephalon Degeneration in Adults With Type 1 Diabetes

Aims: We aimed to assess neurodegenerative changes in the rhinencephalon via magnetic resonance imaging (MRI) and relate it to olfactory function and diabetic peripheral neuropathy (DPN) in adults with type 1 diabetes (T1D). Materials and Methods: Individuals aged 18-65 with T1D duration over 10 years and control healthy subjects underwent olfactory assessment using Sniffin'Sticks and brain MRI to assess volumetric measurements of the olfactory bulbs and piriform cortex thickness. Results: 32 T1D (24 males) aged 43.5 years (IQR: 37.0-48), diabetes duration 24.5 years (IQR: 20.5-27.0), and A1C 7.95% (IQR: 7.4-8.4) were assessed. The control group consisted of 6 healthy adults (4 males) aged 41.0 years (IQR: 36.0-48.0). Significantly lower olfactory test results in TDI (threshold-differentiation-identification) (31.5 (IQR: 28.7-33.6) vs. 34.1 (IQR: 33.2-37.2), p = 0.02) were obtained in the T1D as compared to the controls. Summarized olfactory bulb (OB) volumes and thickness of the left pyriform cortex were significantly smaller in T1D than in controls (65.8 mm3 (IQR: 57.9-71.7) vs. 75.8 mm3 (IQR: 74.8-76.7); p = 0.0005 and 3.1 mm (IQR: 2.7-3.4) vs. 3.6 mm (IQR: 3.5-4.1); p =0.02). Patients with DPN had significantly smaller OB volumes than patients without DPN (58.1 mm3 (IQR: 54.0-70.9) vs. 69.8 mm3 (IQR: 65.0-72.2); p = 0.02). Tobacco smoking (β: -7.89; p = 0.013) and DPN (β:-7.02; p = 0.015) proved to be independent predictors of OB volume. Conclusions: In adults with a long history of T1D, olfactory function and structures are impaired. The presence of diabetic neuropathy and ongoing smoking addiction might be considered predictors of the degradation of rhinencephalon structures in people with T1D.

Association of prior military service with olfactory function among older adults

Objective

Olfactory dysfunction (OD) is a condition primarily affecting older adults. Several factors have been implicated in OD, such as age, socioeconomic status, and neurodegenerative disease; however, the effect of military service still requires additional investigation. Here, we aim to determine if there is an association between prior military service and OD among older adults.

Methods

This cross-sectional study included 2268 adults from Round 1 of the National Social Life, Health, and Aging Project. OD was defined as 0-3 odors correctly identified on the 5-item Sniffin' Sticks test. Bivariate analysis was conducted to calculate crude odds ratios (cOR) for the association of prior military service with OD and identify covariates for regression. Associations between prior military service and OD were assessed using logistic regression, and adjusted odds ratios (aOR) were calculated controlling for age, gender, race/ethnicity, education, stroke history, dementia, diabetes, and mental health. All analyses were weighted using survey weights to account for sampling design.

Results

OD was present in 489 adults (21.6%). Among those with OD, the average age was 71.0 ± 7.9 years, whereas the average age in those without OD was 67.0 ± 7.2 years. Among adults with OD, 34.4% reported prior military service, compared to 27.7% of adults without OD (cOR = 1.37; 95% CI: 1.05-1.79). However, after adjusting for covariates, prior military service was not associated with OD (aOR: 1.09; 95% CI: 0.79-1.50). Older age (aOR: 1.07; 95% CI: 1.05-1.09) and worse mental health (aOR: 1.68; 95% CI: 1.14-2.49) were associated with OD.

Conclusion

Prior military service was not associated with OD among older adults after controlling for covariates. More nuanced research is needed to examine correlations between OD and specific elements of military service such as duration, toxin exposure, and head trauma.Level of Evidence: Level 4.

Olfactory function in diabetes mellitus

Diabetes mellitus (DM) is an increasingly common disease in both children and adults. In addition to neuronal and/or vascular disorders, it can cause chemosensory abnormalities including olfactory deterioration. The purpose of this article is to summarize current knowledge on olfactory function in DM, highlighting the impact of co-morbidities, especially obesity, thyroid dysfunction, chronic kidney disease and COVID-19 on olfactory outcomes. Research to date mostly shows that olfactory impairment is more common in people with diabetes than in the general population. In addition, the presence of concomitant diseases is a factor increasing olfactory impairment. Such a correlation was shown for type 1 diabetes, type 2 diabetes and gestational diabetes. At the same time, not only chronic diseases, but also DM in acute conditions such as COVID-19 leads to a higher prevalence of olfactory disorders during infection. Analyzing the existing literature, it is important to be aware of the limitations of published studies. These include the small number of patients studied, the lack of uniformity in the methods used to assess the sense of smell, frequently relying on rated olfactory function only, and the simultaneous analysis of patients with different types of diabetes, often without a clear indication of diabetes type. In addition, the number of available publications is small. Certainly, further research in this area is needed. From a practical point of view decreased olfactory performance may be an indicator for central neuropathy and an indication for assessing the patient's nutritional status, examining cognitive function, especially in older patients and performing additional diagnostic tests, such as checking thyroid function, because all those changes were correlated with smell deterioration.

Use of nonsteroidal anti-inflammatory drugs and poor olfaction in women

BACKGROUND

It is unclear whether regular use of nonsteroidal anti-inflammatory drugs (NSAIDs) is associated with poor olfaction in older adults.

METHODS

We selected 4020 participants, aged 50 to 79 years in 2018, from 36,492 eligible participants in the National Institute of Environmental Health Sciences Sister Study, according to their self-reported olfaction status. Of these, 3406 women completed the 12-item Brief Smell Identification Test. We defined poor olfaction as a test score ≤9 in the primary analysis. We then estimated odds ratios (ORs) and 95% confidence intervals (CIs) from weighted logistic models, accounting for the study design, missing exposures/outcomes, and covariates.

RESULTS

Overall, NSAID use was not associated with poor olfaction. However, we found evidence for potential multiplicative interactions. Specifically, the OR comparing regular versus never use of aspirin was 1.8 (95% CI, 1.1-3.2) among women who had not regularly used nonaspirin NSAIDs, while the corresponding OR was 0.8 (95% CI, 0.5-1.2) among nonaspirin NSAID users (P for interaction = 0.016). Similar results were seen for ibuprofen alone versus ibuprofen with other NSAID use (P for interaction = 0.010). Among women using either drug alone, associations with poor olfaction increased with increasing duration and cumulative dose. Post hoc analyses showed that the interactions could not be readily explained by potential biases. Other NSAIDs were not associated with olfaction.

CONCLUSION

Long-term regular use of aspirin or ibuprofen was associated with poor olfaction among women who never regularly used other types of NSAIDs. These preliminary findings warrant independent confirmation.

Association between social determinants of health and olfactory dysfunction in older adults: A population-based analysis

BACKGROUND

Social determinants of health (SDoH) are environmental conditions that influence health outcomes. As olfactory dysfunction (OD) in older individuals is associated with increased morbidity and mortality, we sought to investigate the impact of specific SDoH on olfactory function.

METHODS

A cross-sectional analysis of the Health, Aging and Body Composition Study, a US population-based epidemiologic cohort study, was performed. Olfactory function was assessed utilizing both a self-report and a psychophysical olfactory test (CC-SIT test). Multivariable logistic regressions were performed to examine associations between specific SDoH with self-reported anosmia (sOD) and objective anosmia (oOD) as assessed by psychophysical testing. Differences in sensitivity and specificity were evaluated with sample tests for equality of proportions.

RESULTS

Of 2219 participants, 13% had oOD and 18% had objective hyposmia; only 10% had sOD. Individuals identifying as Black race had higher odds of oOD (odds ratio [OR]:1.41, 95% confidence interval [CI]:1.02-1.95), while females and those reporting family incomes ≥$50,000 had lower odds of oOD (OR: 0.46, CI:0.34-0.62; OR:0.52, CI:0.29-0.93), adjusting for covariates. No specific SDoH was significantly associated with sOD. The sensitivity and specificity of sOD for oOD was 23.1% and 92.0%, respectively. sOD had greater sensitivity in females than males (30.8% vs. 18.8%, p = 0.030), while specificity varied significantly depending on family income (range: 90.0%-94.8%, p = 0.033).

CONCLUSIONS

Utilizing a large population-based study, we find disparities in the prevalence and self-recognition of OD among individuals of different gender, race, and income levels. Further effort is needed to evaluate factors propagating these disparities and to raise awareness of OD across all patient populations.

Cranial Nerve Affection in Adolescents with Type 1 Diabetes Assessed by Corneal Confocal Microscopy, Smell and Taste Tests

Aim

To determine whether adolescents with type 1 diabetes (T1D) have morphological changes of the corneal nerve fibers and reduced smell and taste function compared to healthy control subjects as a sign of cranial nerve affection and to evaluate possible associated risk factors for cranial nerve affection.

Methods

The study was a part of the T1DANES study including 60 adolescents (15-<19 years) and 23 healthy age-matched controls. First, clinical and biochemical data on the participants were obtained, and the second step involved a test day with neurological examinations including corneal confocal microscopy (CCM), olfactory testing with Sniffin' Sticks, and gustatory assessment with taste-drop test.

Results

The adolescents with T1D (mean diabetes duration 9.8 years, mean HbA1c 61 mmol/mol) had lower CCM parameters (corneal nerve fiber density, corneal nerve branch density, corneal nerve fiber length, and corneal nerve fiber fractal dimension) compared to control subjects (all p < 0.05). No differences in total score for smell test (p = 0.66) and taste test (p = 0.47) were found, but adolescents with T1D had reduced ability to taste sweet (p < 0.01). In total, 24% had two or more reduced CCM parameters, 12% had reduced smell test, and 23% had abnormal taste test. Higher waist to height ratio (WHtR) was the only risk factor found for reduced corneal nerve fiber density, and higher BMI-SDS and WHtR were found for impaired taste function. Having abnormal smell test increased the risk for having abnormal taste perception, and vice versa.

Conclusion

Up to 29% of adolescents with T1D had abnormal test scores indicating cranial nerve affection. Lower corneal nerve fiber density and reduced ability to taste sweet were found in adolescents with T1D compared to control subjects. Clinical attention to smell and taste function seems important because it requires intervention for advising adolescents with impaired smell and taste function.

Application of Artificial Neural Networks (ANN) to Elucidate the Connections among Smell, Obesity with Related Metabolic Alterations, and Eating Habit in Patients with Weight Excess

Obesity is a severe health problem linked to an increased risk of comorbidity and mortality and its etiopathogenesis includes genetic, epigenetic, microbiota composition, and environmental factors, such as dietary habits. The olfactory system plays an important role in controlling food intake and meal size, influencing body weight and energy balance. This study aims to identify the connection between olfactory function and clinical and nutritional aspects related to weight excess in a group of 68 patients with overweight or obesity. All participants underwent the evaluation of olfactory function, anthropometric data (weight, height, BMI, waist circumference), clinical data (hypertension, disglycemia, dyslipidemia, metabolic syndrome), and adherence to the Mediterranean diet (Mediterranean Diet Score). A fourth-generation artificial neural network data mining approach was used to uncover trends and subtle associations between variables. Olfactory tests showed that 65% of patients presented hyposmia. A negative correlation was found between olfactory scores and systolic blood pressure, fasting plasma glucose, and triglycerides levels, but a positive correlation was found between olfactory scores and the Mediterranean diet score. The methodology of artificial neural networks and the semantic connectivity map "Auto-Contractive Map" highlighted the underlying scheme of the connections between the variables considered. In particular, hyposmia was linked to obesity and related metabolic alterations and the male sex. The female sex was connected with normosmia, higher adherence to the Mediterranean diet, and normal values of blood pressure, lipids, and glucose levels. These results highlight an inverse correlation between olfactory skills and BMI and show that a normosmic condition, probably because of greater adherence to the Mediterranean diet, seems to protect not only from an excessive increase in body weight but also from associated pathological conditions such as hypertension and metabolic syndrome.

Pathophysiology of SARS-CoV-2 Infection of Nasal Respiratory and Olfactory Epithelia and Its Clinical Impact

PURPOSE OF REVIEW

While the predominant cause for morbidity and mortality with SARS-CoV-2 infection is the lower respiratory tract manifestations of the disease, the effects of SARS-CoV-2 infection on the sinonasal tract have also come to the forefront especially with the increased recognition of olfactory symptom. This review presents a comprehensive summary of the mechanisms of action of the SARS-CoV-2 virus, sinonasal pathophysiology of COVID-19, and the correlation with the clinical and epidemiological impact on olfactory dysfunction.

RECENT FINDINGS

ACE2 and TMPRSS2 receptors are key players in the mechanism of infection of SARS-CoV-2. They are present within both the nasal respiratory as well as olfactory epithelia. There are however differences in susceptibility between different groups of individuals, as well as between the different SARS-CoV-2 variants. The sinonasal cavity is an important route for SARS-CoV-2 infection. While the mechanism of infection of SARS-CoV-2 in nasal respiratory and olfactory epithelia is similar, there exist small but significant differences in the susceptibility of these epithelia and consequently clinical manifestations of the disease. Understanding the differences and nuances in sinonasal pathophysiology in COVID-19 would allow the clinician to predict and counsel patients suffering from COVID-19. Future research into molecular pathways and cytokine responses at different stages of infection and different variants of SARS-CoV-2 would evaluate the individual clinical phenotype, prognosis, and possibly response to vaccines and therapeutics.

Food odor perception promotes systemic lipid utilization

Food cues during fasting elicit Pavlovian conditioning to adapt for anticipated food intake. However, whether the olfactory system is involved in metabolic adaptations remains elusive. Here we show that food-odor perception promotes lipid metabolism in male mice. During fasting, food-odor stimulation is sufficient to increase serum free fatty acids via adipose tissue lipolysis in an olfactory-memory-dependent manner, which is mediated by the central melanocortin and sympathetic nervous systems. Additionally, stimulation with a food odor prior to refeeding leads to enhanced whole-body lipid utilization, which is associated with increased sensitivity of the central agouti-related peptide system, reduced sympathetic activity and peripheral tissue-specific metabolic alterations, such as an increase in gastrointestinal lipid absorption and hepatic cholesterol turnover. Finally, we show that intermittent fasting coupled with food-odor stimulation improves glycemic control and prevents insulin resistance in diet-induced obese mice. Thus, olfactory regulation is required for maintaining metabolic homeostasis in environments with either an energy deficit or energy surplus, which could be considered as part of dietary interventions against metabolic disorders.

Impact of Systemic Diseases on Olfactory Function in COVID-19 Infected Patients

Background

COVID-19 (SARS-CoV-2/2019-nCoV) is now a major public health threat to the world. Olfactory dysfunctions (ODs) are considered potential indicating symptoms and early case identification triaging for coronavirus disease 2019 (COVID-19). The most common reported comorbidities are diabetes mellitus, chronic lung disease, and cardiovascular disease. The objective of this study was to evaluate prevalence of different types of smell disorders in patients with laboratory-confirmed COVID-19 infection and impact of involved systemic diseases.

Methodology

A cross-sectional retrospective study has been done for patients with laboratory-confirmed COVID-19 infection (mild-to-moderate). The data collected from patient's files and developed online electronic questionnaire (WhatsApp) based on the patients most common and recurrent reported data including: a) symptoms of olfactory dysfunction and associated covid19 symptoms fever and headache, cough, sore throat, pneumonia, nausea, vomiting and diarrhea, arthralgia and myalgia and taste dysfunction. b) Associated systemic diseases including: diabetes, hypertension, asthma, chronic renal disease, chorionic liver disease and hypothyroidism.

Results

Of 308 patients confirmed with Covid-19 infection, (72.4%) developed OD distributed as follows; complete anosmia (57.8%), troposmia (8.4%), hyposmia (2.9%), partial anosmia (2.6%) and euosmia (0.6%). Significantly increased prevalence of diabetes, hypertension asthma in the group with olfactory dysfunction (p < 0.001), chronic liver disease (p = 0.005), and hypothyroidism (p = 0.03).

Conclusion

The development of ODs after Covid-19 infection was associated with mild disease form and lower hospitalization. In addition, it showed significant relationship with preexisting systemic diseases. Anosmia is the common modality of ODs.

Cardiovascular Risk Stratification in Diabetic Retinopathy via Atherosclerotic Pathway in COVID-19/Non-COVID-19 Frameworks Using Artificial Intelligence Paradigm: A Narrative Review

Diabetes is one of the main causes of the rising cases of blindness in adults. This microvascular complication of diabetes is termed diabetic retinopathy (DR) and is associated with an expanding risk of cardiovascular events in diabetes patients. DR, in its various forms, is seen to be a powerful indicator of atherosclerosis. Further, the macrovascular complication of diabetes leads to coronary artery disease (CAD). Thus, the timely identification of cardiovascular disease (CVD) complications in DR patients is of utmost importance. Since CAD risk assessment is expensive for low-income countries, it is important to look for surrogate biomarkers for risk stratification of CVD in DR patients. Due to the common genetic makeup between the coronary and carotid arteries, low-cost, high-resolution imaging such as carotid B-mode ultrasound (US) can be used for arterial tissue characterization and risk stratification in DR patients. The advent of artificial intelligence (AI) techniques has facilitated the handling of large cohorts in a big data framework to identify atherosclerotic plaque features in arterial ultrasound. This enables timely CVD risk assessment and risk stratification of patients with DR. Thus, this review focuses on understanding the pathophysiology of DR, retinal and CAD imaging, the role of surrogate markers for CVD, and finally, the CVD risk stratification of DR patients. The review shows a step-by-step cyclic activity of how diabetes and atherosclerotic disease cause DR, leading to the worsening of CVD. We propose a solution to how AI can help in the identification of CVD risk. Lastly, we analyze the role of DR/CVD in the COVID-19 framework.

Olfactory disfunction and diabetic complications in type 2 diabetic patients: a pilot study

PURPOSE

Scarce information on the prevalence and characteristics of olfactory disfunction (OD) in type 2 diabetic (T2D) patients are available. The aims of this study were (1) to assess the olfactory function in T2D patients and to compare it with a control group of individuals without T2D, and (2) to evaluate the differences in OD within T2D patients according to the presence of diabetic complications.

METHODS

A group of 39 T2D patients and a control group of 39 healthy individuals were enrolled. Each subject underwent an evaluation of the olfactory performance using the Sniffing Olfactory Screening Test (SOST) and completed a questionnaire assessing the subjective perception of olfaction. According to the presence of diabetic complications, the group of T2D patients was divided into two subgroups. Non-parametric tests and regression analysis were used for statistical analysis.

RESULTS

No differences in the subjective perception of olfaction were demonstrated among T2D patients (with and without complications) and controls. A significant difference for the SOST score was demonstrated among the different groups. In particular, OD was more frequent in T2D patients than in controls. In addition, OD was far more frequent in T2D patients with complications. Regression analysis did not demonstrate any significant association between OD and clinical/demographic characteristics of T2D patients.

CONCLUSION

T2D patients were more frequently affected by OD. The subgroup analysis suggested a possible relationship between OD and diabetic complications since patients with T2D diabetic complications demonstrated lower olfactory abilities than controls subjects and T2D patients without diabetic complications.

Olfaction in the context of obesity and diabetes: Insights from animal models to humans

The olfactory system is at the crossroad between sensory processing and metabolic sensing. In addition to being the center of detection and identification of food odors, it is a sensor for most of the hormones and nutrients responsible for feeding behavior regulation. The consequences of modifications in body homeostasis, nutrient overload and alteration of this brain network in the pathological condition of food-induced obesity and type 2 diabetes are still not elucidated. The aim of this review was first to use both humans and animal studies to report on the current knowledge of the consequences of obesity and type 2 diabetes on odorant threshold and olfactory perception including identification discrimination and memory. We then discuss how olfactory processing can be modified by an alteration of the metabolic homeostasis of the organism and available elements on pharmacological treatments that regulate olfaction. We focus on data within the olfactory system but also on the interactions between the olfactory system and other brain networks impacted by metabolic diseases.

Alterations in sweet taste function in adults with diabetes mellitus: a systematic review and potential implications

Diet therapy for diabetes involves controlling carbohydrate intake in order to manage blood glucose concentrations. Simple carbohydrates, like sucrose, quickly and potently raise blood glucose when ingested, and are typically perceived as sweet. Sweetness is innately pleasurable and contributes to the positive hedonic evaluation of foods and beverages. There is some evidence to suggest that individuals with diabetes mellitus may be less able to detect sweetness, which could result in increased intake and, thus, more difficulty managing blood glucose. A systematic review that included PubMed, PsycInfo, and Embase databases was conducted. Inclusion criteria included observational studies that investigated the sweet taste function of adults with and without diabetes mellitus (Prospero CRD42021225058). The quality of the final included studies was assessed using the Academy of Nutrition and Dietetics' Evidence Analysis Library Quality Criteria Checklist: Primary Research tool. Eighteen studies that compared sweet taste thresholds, intensity ratings, or hedonic responses in adults both with and without diabetes were included. Differences in sweet taste thresholds, both detection and recognition, indicated that individuals with diabetes were less sensitive than healthy controls. The same findings were observed for intensity ratings. Only two studies examined hedonic responses; results were inconclusive.

The microvascular hypothesis underlying neurologic manifestations of long COVID-19 and possible therapeutic strategies

With the ongoing distribution of the coronavirus disease (COVID) vaccines, the pandemic of our age is ending, leaving the world to deal with its well-documented aftereffects. Long COVID comprises a variety of symptoms, of which the neurological component prevails. The most permeating theory on the genesis of these symptoms builds upon the development of microvascular dysfunction similar to that seen in numerous vascular diseases such as diabetes. This can occur through the peripheral activation of angiotensin-converting enzyme 2 receptors, or through exacerbations of pro-inflammatory cytokines that can remain in circulation even after the infection diminishes. Several drugs have been identified to act on the neurovascular unit to promote repair, such as gliptins, and others. They also succeeded in improving neurologic outcome in diabetic patients. The repurposing of such drugs for treatment of long COVID-19 can possibly shorten the time to recovery of long COVID-19 syndrome.

Association between diabetes mellitus and chronic rhinosinusitis with nasal polyps: A population-based cross-sectional study

OBJECTIVE

To investigate the association between physician-diagnosed diabetes mellitus (DM) and chronic rhinosinusitis (CRS) phenotypes in a national population-based study.

STUDY DESIGN

Retrospective cross-sectional study.

SETTING

Population-based survey data were collected by the Korean National Health and Nutrition Survey between January 2008 and December 2012.

PARTICIPANTS AND METHODS

A total of 34 670 participants aged over 19 years were enrolled in the Korea National Health and Nutrition Examination Surveys from 2008 to 2012. The relationship of CRS prevalence, with and without nasal polyps, with physician-diagnosed DM and non-DM were assessed. Differences in sinonasal symptoms between patients with and without DM were analysed in this cross-sectional study.

RESULTS

A significant association was observed between DM and CRS with nasal polyps after adjustment for multiple variables. No substantial association was observed between DM and CRS without nasal polyps. Among patients with CRS, olfactory dysfunction for >3 months was significantly more frequent in the DM group than in the non-DM group.

CONCLUSION

We demonstrated significant associations between DM and CRS with nasal polyps and olfactory dysfunction among patients with CRS in a large national clinical cohort study. The direct mechanism of the association between DM and CRS with nasal polyps should be further investigated to clarify the pathogenesis of CRS with nasal polyps.

Olfactory dysfunction in cystic fibrosis: Impact of CFTR modulator therapy

BACKGROUND

Elexacaftor-tezacaftor-ivacaftor (ETI) improves pulmonary health and chronic rhinosinusitis (CRS) for people with cystic fibrosis (PwCF), however its impact on olfaction has not been investigated. Olfactory dysfunction impairs quality-of-life (QOL). This study evaluated the impact of ETI on multiple olfactory metrics.

METHODS

Adult PwCF/CRS with CF transmembrane conductance regulator genotype F508del/F508del or F508del/minimal function who clinically initiated ETI participated in a prospective, observational study. Endpoints included changes after 6 months of ETI in quantitative olfactory function (Smell Identification Test, SIT), olfactory QOL (Questionnaire of Olfactory Disorders, QOD) and percent olfactory cleft opacification (%OCO), representing superior nasal cavity inflammation where afferent olfactory neurons are concentrated.

RESULTS

30 PwCF/CRS met inclusion criteria; 25 completed the study. Mean ETI adherence was 93%. At baseline, participants were hyposmic (mean SIT 31.3), had significant %OCO (mean 65.6%), yet reported non-impaired olfactory QOL (mean QOD 6.1). At follow-up, mean SIT worsened mildly (p=0.009), mean %OCO remained stable (p=0.46), and mean QOD improved modestly (p=0.008). No outcomes were impacted by prior modulator use, genotype, nasal polyps, or CF-related diabetes. Prior sinus surgery was associated with QOD improvement (p=0.04). Increased (worse) baseline QOD scores and %OCO were associated with greater improvements (p<0.003), but not SIT (p=0.44).

CONCLUSIONS

ETI was not associated with improvement in quantitative olfaction or olfactory cleft opacification after 6 months. PwCF/CRS have hyposmia but do not report impairment in olfactory QOL. Further study to investigate mechanisms explaining olfactory dysfunction and whether olfaction improves with greater duration of ETI or in younger age groups is warranted.

Age-Related Olfactory Decline Is Associated With Levels of Exercise and Non-exercise Physical Activities

Objective: This cross-sectional study evaluates the impact of active or non-active lifestyle in terms of physical, cognitive and social activity on the olfactory function in Elderly Subjects (ES) and aims at looking for a correlation between the time devoted to life activities and the score obtained during the olfactory tests by each individual.

Methods: One hundred and twenty-two elderly volunteers were recruited in Sardinia (Italy) and divided into active ES (n = 60; 17 men, 43 women; age 67.8 ± 1.12 years) and inactive ES (n = 62; 21 men, 41 women, age 71.1 ± 1.14 years) based on their daily physical activities. The olfactory function was evaluated using the “Sniffin’s Sticks” battery test, while the assessment of daily activities was made by means of personal interviews.

Results: A significant effect of active or inactive lifestyle was found on the olfactory function of ES (F_(1,120) > 10.16; p < 0.005). A positive correlation was found between the olfactory scores and the number of hours per week dedicated to physical activities (Pearson’s r > 0.32, p ≤ 0.014) in both active and inactive ES.

Conclusions: High levels of exercise and non-exercise physical activity are strongly associated with the olfactory function and, consequently, with the quality of life of the elderly. Given the limited physical exercise of elderly people, they can benefit from a more active lifestyle by increasing non-exercise physical activities.

Epidemiological, otolaryngological, olfactory and gustatory outcomes according to the severity of COVID-19: a study of 2579 patients

OBJECTIVE

To investigate prevalence and epidemiological and clinical factors associated with olfactory dysfunction (OD) and gustatory dysfunction (GD) in COVID-19 patients according to the disease severity.

STUDY DESIGN

Cross-sectional study.

METHODS

A total of 2579 patients with a positive diagnosis of COVID-19 were identified between March 22 and June 3, 2020 from 18 European hospitals. Epidemiological and clinical data were extracted. Otolaryngological symptoms, including OD and GD, were collected through patient-reported outcome questionnaire and Sniffin'Sticks tests were carried out in a subset of patients.

RESULTS

A total of 2579 patients were included, including 2166 mild (84.0%), 144 moderate (5.6%) and 269 severe-to-critical (10.4%) patients. Mild patients presented an otolaryngological picture of the disease with OD, GD, nasal obstruction, rhinorrhea and sore throat as the most prevalent symptoms. The prevalence of subjective OD and GD was 73.7 and 46.8%, and decreases with the severity of the disease. Females had higher prevalence of subjective OD and GD compared with males. Diabetes was associated with a higher risk to develop GD. Among the subset of patients who benefited from psychophysical olfactory evaluations, there were 75 anosmic, 43 hyposmic and 113 normosmic patients. The prevalence of anosmia significantly decreased with the severity of the disease. Anosmia or hyposmia were not associated with any nasal disorder, according to SNOT-22.

CONCLUSION

OD and GD are more prevalent in patients with mild COVID-19 compared with individuals with moderate, severe or critical diseases. Females might have a higher risk of developing OD and GD compared with males.

Impact of renal replacement therapies on olfactory ability: results of a cross-sectional case control study

Introduction

Several studies have suggested that chronic kidney disease (CKD) may be associated with olfactory impairment. However, to date, the impact of renal replacement therapies has only been partly defined.

Methods

We tested the olfactory function of 235 participants [50 kidney transplant recipients (KT), 49 hemodialyzed patients (HD), 30 peritoneal dialysis patients (PD), 51 patients with CKD not on dialysis (ND-CKD) and 55 healthy subjects (HS)] by the Sniffin’ Sticks test (Burghardt®, Wedel, Germany), including the sub-tests for the determination of odor threshold (T), odor discrimination (D), odor identification (I). Each subtest result was then summed up to a composite score, known as the TDI score. The Sino-Nasal Outcome Test-22 (SNOT22), Montreal Cognitive Assessment (MoCA) test and olfactory function Visual Analogue Scale (ofVAS) were also performed.

Results

The mean TDI score was significantly lower (and consistent with hyposmia), in HD, PD and ND-CKD compared to HS and KT (ANOVA p < 0.001). Similar results were observed in the I and D tests, and with the T score, though with regard to the latter, only in PD and ND-CKD patients. Multiple comparisons among groups demonstrated no significant differences between KT and HS. After adjustments for confounding factors, a significant linear association was found between both urea (β − 0.03, p < 0.003) and eGFR (β 0.08, p < 0.001) with TDI score. No significant association was observed between the TDI score and the ofVAS score (p = 0.293).

Conclusions

Olfactory impairment affects a large number of CKD patients in the pre-dialysis phase as well as those on dialysis. Kidney transplantation may reverse this condition with a possible positive impact on the quality of life and social behaviors/relationships.

Graphic abstract

Supplementary Information

The online version contains supplementary material available at 10.1007/s40620-021-00983-6.

Development of the Spanish Version of Sniffin's Sticks Olfactory Identification Test: Normative Data and Validity of Parallel Measures

The Sniffin' Sticks Olfactory Identification Test is a tool for measurement of olfactory performance developed in Germany and validated in several countries. This research aims to develop the Spanish version of the Sniffin' Sticks Olfactory Identification Test and obtain normative values for the Spanish population. The parameters are free recall and subjective intensity of odorants are included. The influence of possible demographic covariates such as sex, age, smoking, or educational level are analyzed, and the items that best discriminate are studied. In addition, the internal structure validity of the blue and purple versions is studied as a parallel measure, and a cultural adaptation of the purple version is carried out. For this, three independent samples of normosmic healthy volunteers were studied. To obtain normative values, the sample was of 417 participants (18-89 years). For the internal structure validity study of both versions, the sample was 226 (18-70 years), and for familiarity of the purple version, the sample was 75 participants (21-79 years). Results indicated that men and women and smokers and non-smokers perform equally. However, differences were found as age progresses, being more pronounced after 60 years old in all three measurements of the identification test. This research also provides the items that best discriminate in the blue version and a cultural adaptation for the purple version. In conclusion, the Sniffin' Sticks Odor Identification Test is a suitable tool for olfactory assessment in the Spanish population. The instrument has been expanded with two new scores, and normative data as a function of age are provided. Its parallel version also seems appropriate for testing, as items have been culturally adapted and evidence of internal structure validity for both versions is reported.

Differences in taste and smell perception between type 2 diabetes mellitus patients and healthy controls

BACKGROUND AND AIMS

The senses of taste and smell are essential determinants of food choice, which in turn may contribute to the development of chronic diseases, including diabetes. Although past studies have evaluated the relationship between type 2 diabetes mellitus (DM2) and senses disorders, this relationship remains controversial. In this study, we evaluated taste and smell perception in DM2 patients and healthy controls (HC). Moreover, we analyzed the association of chemosensory impairments with anthropometric and clinical outcomes (e.g. Body Mass Index (BMI), Fasting blood glucose (FBG), drugs, cardiovascular diseases (CVD), and hypertension) in DM2 patients.

METHODS AND RESULTS

The study included 94 DM2 patients and 244 HC. Taste recognition for 6-n-propylthiouracil (PROP), quinine, citric acid, sucrose, and sodium chloride (NaCl) compounds was assessed using a filter paper method, while smell recognition of 12 odorants was performed using a Sniffin' sticks test. We found that a higher percentage of DM2 patients showed identification impairment in salt taste (22% vs. 5%, p-value<0.0009) and smell recognition (55% vs. 27%, p-value = 0.03) compared to HC. We also observed that 65% of hypertensive DM2 subjects presented smell identification impairment compared to 18% of non-hypertensive patients (p-value = 0.019). Finally, patients with impairments in both taste and smell showed elevated FBG compared to patients without impairment (149.6 vs.124.3 mg/dL, p-value = 0.04).

CONCLUSION

The prevalence of taste and smell identification impairments was higher in DM2 patients compared to HC, and a possible relationship with glycemic levels emerged.

Relationships between Cognitive Function and Odor Identification, Balance Capability, and Muscle Strength in Middle-Aged Persons with and without Type 2 Diabetes

AIM

We investigated the relationship between cognitive function and olfactory and physical functions in middle-aged persons with and without type 2 diabetes (T2D) to examine the potential of olfactory and physical functions as biomarkers for early cognitive impairment.

METHODS

Enrolled were 70 T2D patients (age 40 to <65 y) and 81 age-matched control participants without diabetes. Cognitive function was assessed by the Montreal Cognitive Assessment (MoCA), Trail Making Test parts A and B (TMT-A/-B), Wisconsin Card Sorting Test (WCST), Quick Inventory of Depressive Symptomatology Self-Report (QIDS), and Starkstein Apathy Scale (SAS). Multiple linear regression analyses were performed.

RESULTS

Odor identification was an independent determinant shown in the results of the TMT-A in the entire participant group and was independently associated with the MoCA and TMT-B in the T2D group. Balance capability assessed with a stabilometer was independently associated with all cognitive function tests except for QISD and SAS in the entire participant group and the T2D group and was independently associated with TMT-A in the control group. Knee extension strength was independently associated with the SAS in the entire participant group and the T2D group.

CONCLUSIONS

Odor identification, balance capability, and knee extension strength were potential markers for cognitive decline in middle-aged persons with T2D.

Spanish Validation for Olfactory Function Testing Using the Sniffin' Sticks Olfactory Test: Threshold, Discrimination, and Identification

The assessment of olfactory function is becoming increasingly relevant, especially in cases of cognitive decline (i.e., neurodegenerative diseases), where olfactory alterations may be relevant as potential early biomarkers. The Sniffin' Sticks Olfactory Test, developed in Germany and validated in several countries, is an objective measure of olfactory performance. This study aims to validate this test in a Spanish sample. This study included 209 healthy normosmic volunteers (154 females and 55 males) aged between 20 to 79 years (mean age = 50.11 ± 15.18 years) as the normative sample. From this group, 22 participants were retested in order to obtain test-retest reliability evidence. Odor familiarity for descriptors in the olfactory identification test was also studied on an independent healthy sample (n = 69), and required cultural modifications were applied. Results indicate that men and women, as well as smokers and non-smokers, performed equally in every test. However, significant differences were found between age groups in every score. The general trend is that olfactory function progressively decreases as a function of age, the elderly group (+60 years) being the one with the lowest scores. In conclusion, this normative data, in addition to the test's cultural modifications, allows the Sniffin' Sticks Olfactory Test to be administered on a Spanish population.

Western Diet Accelerates the Impairment of Odor-Related Learning and Olfactory Memory in the Mouse

Olfactory dysfunction could be an early indicator of cognitive decline in type 2 diabetes (T2D). However, whether obesity affects olfaction in people with T2D is unclear. This question needs to be addressed, because most people with T2D are obese. Importantly, whether different contributing factors leading to obesity (e.g., different components of diet or gain in weight) affect specific olfactory functions and underlying mechanisms is unknown. We examined whether two T2D-inducing obesogenic diets, one containing a high proportion of fat (HFD) and one with moderate fat and high sugar (Western diet, WD), affect odor detection/discrimination, odor-related learning, and olfactory memory in the mouse. We also investigated whether the diets impair adult neurogenesis, GABAergic interneurons, and neuroblasts in the olfactory system. Here, we further assessed olfactory cortex volume and cFos expression-based neuronal activity. The WD-fed mice showed declined odor-related learning and olfactory memory already after 3 months of diet intake (p = 0.046), although both diets induced similar hyperglycemia and weight gain compared to those of standard diet-fed mice (p = 0.0001 and p < 0.0001, respectively) at this time point. Eight months of HFD and WD diminished odor detection (p = 0.016 and p = 0.045, respectively), odor-related learning (p = 0.015 and p = 0.049, respectively), and olfactory memory. We observed no changes in the investigated cellular mechanisms. We show that the early deterioration of olfactory parameters related to learning and memory is associated with a high content of sugar in the diet rather than with hyperglycemia or weight gain. This finding could be exploited for understanding, and potentially preventing, cognitive decline/dementia in people with T2D. The mechanisms behind this finding remain to be elucidated.

Correlates of olfactory impairment in middle-aged non-diabetic Caucasian subjects with stage I-II obesity

PURPOSE

This study evaluates among middle-aged subjects with obesity the prevalence of olfactory impairment (OI) with respect to normative values and its correlation with body composition, cognition, sleep quality, and inflammation.

METHODS

In 60 (31 women, 29 men) volunteers with a body mass index ≥ 30 to ≤ 40 kg/m², aged ≥ 50 to ≤ 70 years, we assessed olfaction by the Sniffin' Stick test. We measured anthropometrics, body composition and metabolic profiles and evaluated cognition by the MiniMental State Examination (MMSE) and sleep disturbances by the Insomnia Severity Index (ISI). Patients were classified into two groups according to a total olfactory score (odor Threshold, Discrimination, Identification, TDI) below or above the 25th percentile from age and gender-adjusted normative data.

RESULTS

Overall, 25 subjects (42%) had OI (TDI < 25th percentile). The largest differences between subjects with and without OI were observed in discrimination and identification scores, with a large overlap in olfactory threshold. Subjects with an abnormal TDI showed significantly higher fat mass index, ISI scores and urinary neopterin and lower MMSE scores than those without OI. By multivariable logistic regression, MMSE, ISI score and urinary neopterin were significantly associated to OI.

CONCLUSIONS

Among middle-aged subjects with stage I and II obesity, OI is highly prevalent and is independently associated with poor self-reported sleep quality, lower cognition scores and higher levels of the inflammatory marker neopterin.

Association of olfactory neuropathy spectrum disorder and Wolff-Parkinson-White syndrome: A Report of a case

Olfactory neuropathy spectrum disorder is characterized by hyposmia or anosmia and hypoplastic or absent olfactory bulbs. There may be an association between olfactory neuropathy spectrum disorder and Wolff-Parkinson-White syndrome.

Smell and taste dysfunction during the COVID-19 outbreak: a preliminary report

In late December 2019, in Wuhan (China), health authorities reported several clusters of pneumo- nia of unknown cause, subsequently attributed to a novel coronavirus, identified as Severe Acute Respiratory Syndrome-Coronavirus 2. Anosmia and dysgeusia have been reported as particular symptoms.4,5  Notably, these sensory symptoms seem to have a peculiar trend, such as usually precede the onset of respiratory symp- toms. So, they have been defined as "sentinel" symptoms. We presented a series of COVID-19 patients. Anos- mia and dysgeusia frequently preceded respiratory complaints. Anosmia and dysgeusia seem to be short-lived and self-resolving in COVID-19, thus a neurotoxic effect swiftly disappearing and/or cytopathic damage could be hypothesized similarly to other viral infections.