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

Alterations of Cerebral Blood Flow and Its Connectivity in Olfactory-Related Brain Regions of Type 2 Diabetes Mellitus Patients

To investigate the alteration of cerebral blood flow (CBF) and its connectivity patterns in olfactory-related regions of type 2 diabetes mellitus (T2DM) patients using arterial spin labeling (ASL). Sixty-nine patients with T2DM and 63 healthy controls (HCs) underwent ASL scanning using 3.0T magnetic resonance imaging. We compared the CBF values of the olfactory-related brain regions between the two groups and analyzed the correlation between their changes and clinical variables. We also used these regions as seeds to explore the differences in CBF connectivity patterns in olfactory-related brain regions between the T2DM patients and HCs. Compared with the HC group, the CBF of the right orbital part of the inferior frontal gyrus (OIFG), right insula, and bilateral olfactory cortex was decreased in the T2DM patients. Moreover, the duration of the patients was negatively correlated with the CBF changes in the right OIFG, right insula, and right olfactory cortex. The CBF changes in the right OIFG were positively correlated with the Self-Rating Depression Scale scores, those in the right insula were negatively correlated with the max blood glucose of continuous glucose, and those in the right olfactory cortex were negatively correlated with the mean blood glucose of continuous glucose. In addition, the T2DM patients also showed decreased CBF connectivity between the right OIFG and the left temporal pole of the middle temporal gyrus and increased CBF connectivity between the right medial orbital part of the superior frontal gyrus and the right orbital part of the superior frontal gyrus and between the right olfactory cortex and the bilateral caudate and the left putamen. Patients with T2DM have decreased CBF and altered CBF connectivity in multiple olfactory-related brain regions. These changes may help explain why olfactory dysfunction occurs in patients with T2DM, thus providing insights into the neuropathological mechanism of olfactory dysfunction and cognitive decline in T2DM patients.

Neuroprotective role of insulin-like growth factor 1 in auditory and other nervous systems

Insulin-like growth factor 1 (IGF1) exerts an influence on almost every organ system in the body and plays an important role in growth, development, and metabolism. In the nervous system, IGF1 acts by promoting the development and growth of neurons and glial cells, differentiation of Schwann cells and their migration to axons, neurite outgrowth, and neuronal survival. The lack of IGF1 is associated with several pathological conditions, including severe prenatal growth retardation, postnatal growth failure, microcephaly, mental retardation, and bilateral sensorineural hearing loss. In addition to its physiological effects, based on the findings of in vivo and in vitro experiments and clinical trials, IGF1 is considered to play a potential role in the treatment of various types of neuronal damage. In this review, we discuss the potential use of IGF1 as a therapeutic molecule in the nervous system: (1) auditory system, including hair cells, cochlear ribbon synapses, auditory nerve, and central nervous systems, and (2) other peripheral nervous systems, especially the olfactory system and facial nerve. The role of IGF1 in the progression of age-related sensory deficits, especially hearing loss and olfactory dysfunction, is also discussed. Recent studies on IGF1 demonstrated that exogenous IGF1 can be applied in many fields, thus supporting the continued evaluation of IGF1 as a potential therapeutic molecule. Additional scientific investigations should be conducted to further supplement recent findings.

Manganese-enhanced magnetic resonance imaging method detects age-related impairments in axonal transport in mice and attenuation of the impairments by a microtubule-stabilizing compound

In this study a manganese-enhanced magnetic resonance imaging (MEMRI) method was developed for mice for measuring axonal transport (AXT) rates in real time in olfactory receptor neurons, which project from the olfactory epithelium to the olfactory neuronal layer of the olfactory bulb. Using this MEMRI method, two major experiments were conducted: 1) an evaluation of the effects of age on AXT rates and 2) an evaluation of the brain-penetrant, microtubule-stabilizing agent, Epothilone D for effect on AXT rates in aged mice. In these studies, we improved upon previous MEMRI approaches to develop a method where real-time measurements (32 time points) of AXT rates in mice can be determined over a single (approximately 100 min) scanning session. In the age comparisons, AXT rates were significantly higher in young (mean age ∼4.0 months old) versus aged (mean age ∼24.5 months old) mice. Moreover, in aged mice, eight weeks of treatment with Epothilone D, (0.3 and 1.0 mg/kg) was associated with statistically significant increases in AXT rates compared to vehicle-treated subjects. These experiments conducted in a living mammalian model (i.e., wild type, C57BL/6 mice), using a new modified MEMRI method, thus provide further evidence that the process of aging leads to decreases in AXT rates in the brain and they further support the argument that microtubule-based therapeutic strategies designed to improve AXT rates have potential for age-related neurological disorders.

International consensus statement on allergy and rhinology: Olfaction

BACKGROUND

The literature regarding clinical olfaction, olfactory loss, and olfactory dysfunction has expanded rapidly over the past two decades, with an exponential rise in the past year. There is substantial variability in the quality of this literature and a need to consolidate and critically review the evidence. It is with that aim that we have gathered experts from around the world to produce this International Consensus on Allergy and Rhinology: Olfaction (ICAR:O).

METHODS

Using previously described methodology, specific topics were developed relating to olfaction. Each topic was assigned a literature review, evidence-based review, or evidence-based review with recommendations format as dictated by available evidence and scope within the ICAR:O document. Following iterative reviews of each topic, the ICAR:O document was integrated and reviewed by all authors for final consensus.

RESULTS

The ICAR:O document reviews nearly 100 separate topics within the realm of olfaction, including diagnosis, epidemiology, disease burden, diagnosis, testing, etiology, treatment, and associated pathologies.

CONCLUSION

This critical review of the existing clinical olfaction literature provides much needed insight and clarity into the evaluation, diagnosis, and treatment of patients with olfactory dysfunction, while also clearly delineating gaps in our knowledge and evidence base that we should investigate further.

Distinct Age-Specific Effects on Olfactory Associative Learning in C57BL/6 Substrains

C57BL/6 is the most widely used mouse strain in the laboratories. Two substrains of C57BL/6, C57BL/6J (B6J), and C57BL/6N (B6N) are well-known backgrounds for genetic modification and have been shown difference in quite a few tests, including open field test, rotarod test, and Morris water maze. However, difference between these two substrains in olfaction-dependent behaviors remains unknown. Here, we used olfactory two-alternative choice task, which is modified to have two training stages, to evaluate animals’ ability in instrumental learning and olfactory association. In the first (rule learning) stage, the mice were trained to use the operant chamber to collect water rewards. An odor cue was provided in the procedure, with no indication about reward locations. In the following (discrimination learning) stage, two odor cues were provided, with each indicating a specific water port. The animals were rewarded upon correct port choices following cue deliveries. We found that during young adulthood (7–10 weeks old), proportionally more B6J than B6N mice were able to pass rule learning (58.3% vs. 29.2%) and ultimately acquire this task (54.2% vs. 25%), with the two substrains showing similar pass rates in discrimination learning (92.9% vs. 85.7%). Surprisingly, at a more mature age (17 weeks old), this substrain difference disappeared. Mature B6N mice had a significant improvement in pass percentages of rule learning and overall task, whereas similar improvement was not observed in the B6J counterparts. Instead, mature B6J mice had an improved speed in rule learning and overall task. We further examined behavioral patterns of 8-week-old B6J and B6N mice in the olfactory habituation or dishabituation test. We observed normal olfactory habituation from subjects of both substrains, with the B6J mice exhibiting stronger investigative responses to newly presented odorants. These results reveal for the first time that B6J and B6N mice are different in acquisition processes of a behavioral task that requires instrumental learning and olfactory association, and that maturation appears to employ different effects on these two substrains during these processes. Furthermore, young adult B6J and B6N mice might be similar in olfactory habituation but different in the olfactory aspects of novelty seeking.

Neuroimmunoendocrine Link Between Chronic Kidney Disease and Olfactory Deficits

Chronic kidney disease (CKD) is a multifactorial pathology that progressively leads to the deterioration of metabolic functions and results from deficient glomerular filtration and electrolyte imbalance. Its economic impact on public health is challenging. Mexico has a high prevalence of CKD that is strongly associated with some of the most common metabolic disorders like diabetes and hypertension. The gradual loss of kidney functions provokes an inflammatory state and endocrine alterations affecting several systems. High serum levels of prolactin have been associated with CKD progression, inflammation, and olfactory function. Also, the nutritional status is altered due to impaired renal function. The decrease in calorie and protein intake is often accompanied by malnutrition, which can be severe at advanced stages of the disease. Nutrition and olfactory functioning are closely interconnected, and CKD patients often complain of olfactory deficits, which ultimately can lead to deficient food intake. CKD patients present a wide range of deficits in olfaction like odor discrimination, identification, and detection threshold. The chronic inflammatory status in CKD damages the olfactory epithelium leading to deficiencies in the chemical detection of odor molecules. Additionally, the decline in cognitive functioning impairs the capacity of odor differentiation. It is not clear whether peritoneal dialysis and hemodialysis improve the olfactory deficits, but renal transplants have a strong positive effect. In the present review, we discuss whether the olfactory deficiencies caused by CKD are the result of the induced inflammatory state, the hyperprolactinemia, or a combination of both.

A systematic review of olfactory-related brain structural changes in patients with congenital or acquired anosmia

Brain structural features of healthy individuals are associated with olfactory functions. However, due to the pathophysiological differences, congenital and acquired anosmia may exhibit different structural characteristics. A systematic review was undertaken to compare brain structural features between patients with congenital and acquired anosmia. A systematic search was conducted using PubMed/MEDLINE and Scopus electronic databases to identify eligible reports on anosmia and structural changes and reported according to PRISMA guidelines. Reports were extracted for information on demographics, psychophysical evaluation, and structural changes. Then, the report was systematically reviewed based on various aetiologies of anosmia in relation to (1) olfactory bulb, (2) olfactory sulcus, (3) grey matter (GM), and white matter (WM) changes. Twenty-eight published studies were identified. All studies reported consistent findings with strong associations between olfactory bulb volume and olfactory function across etiologies. However, the association of olfactory function with olfactory sulcus depth was inconsistent. The present study observed morphological variations in GM and WM volume in congenital and acquired anosmia. In acquired anosmia, reduced olfactory function is associated with reduced volumes and thickness involving the gyrus rectus, medial orbitofrontal cortex, anterior cingulate cortex, and cerebellum. These findings contrast to those observed in congenital anosmia, where a reduced olfactory function is associated with a larger volume and higher thickness in parts of the olfactory network, including the piriform cortex, orbitofrontal cortex, and insula. The present review proposes that the structural characteristics in congenital and acquired anosmia are altered differently. The mechanisms behind these changes are likely to be multifactorial and involve the interaction with the environment.

Comparison of Olfactory Tract Diffusion Measures Between Early Stage Parkinson's Disease Patients and Healthy Controls Using Ultra-High Field MRI

BACKGROUND

MRI is a valuable method to assist in the diagnostic work-up of Parkinson's disease (PD). The olfactory tract (OT) has been proposed as a potential MRI biomarker for distinguishing PD patients from healthy controls.

OBJECTIVE

This study aims to further investigate whether diffusion measures of the OT differ between early stage PD patients and healthy controls.

METHODS

Twenty hyposmic/anosmic PD patients, 65 normosmic PD patients, and 36 normosmic healthy controls were evaluated and a 7T diffusion weighted image scan was acquired. Manual seed regions of interest were drawn in the OT region. Tractography of the OT was performed using a deterministic streamlines algorithm. Diffusion measures (fractional anisotropy and mean- radial- and axial diffusivity) of the generated streamlines were compared between groups.

RESULTS

Diffusion measures did not differ between PD patients compared to healthy controls and between hyposmic/anosmic PD patients, normosmic PD patients, and normosmic healthy controls. A positive correlation was found between age and mean- and axial diffusivity within the hyposmic/anosmic PD subgroup, but not in the normosmic groups. A positive correlation was found between MDS-UPDRSIII scores and fractional anisotropy.

CONCLUSION

This study showed that fiber tracking of the OT was feasible in both early stage PD and healthy controls using 7T diffusion weighted imaging data. However, 7T MRI diffusion measures of the OT are not useful as an early clinical biomarker for PD. Future work is needed to clarify the role of other OT measurements as a biomarker for PD and its different subgroups.

Olfactory Function and Markers of Brain Pathology in Non-Demented Individuals with Autosomal Dominant Alzheimer's Disease

BACKGROUND

Olfactory dysfunction is one of the earliest signs of Alzheimer's disease (AD), highlighting its potential use as a biomarker for early detection. It has also been linked to progression from mild cognitive impairment (MCI) to dementia.

OBJECTIVE

To study olfactory function and its associations with markers of AD brain pathology in non-demented mutation carriers of an autosomal dominant AD (ADAD) mutation and non-carrier family members.

METHODS

We analyzed cross-sectional data from 16 non-demented carriers of the Presenilin1 E280A ADAD mutation (mean age [SD]: 40.1 [5.3], and 19 non-carrier family members (mean age [SD]: 36.0 [5.5]) from Colombia, who completed olfactory and cognitive testing and underwent amyloid and tau positron emission tomography (PET) imaging.

RESULTS

Worse olfactory identification performance was associated with greater age in mutation carriers (r = -0.52 p = 0.037). In carriers, worse olfactory identification performance was related to worse MMSE scores (r = 0.55, p = 0.024) and CERAD delayed recall (r = 0.63, p = 0.007) and greater cortical amyloid-β (r = -0.53, p = 0.042) and tau pathology burden (entorhinal: r = -0.59, p = 0.016; inferior temporal: r = -0.52, p = 0.038).

CONCLUSION

Worse performance on olfactory identification tasks was associated with greater age, a proxy for disease progression in this genetically vulnerable ADAD cohort. In addition, this is the first study to report olfactory dysfunction in ADAD mutation carriers with diagnosis of MCI and its correlation with abnormal accumulation of tau pathology in the entorhinal region. Taken together, our findings suggest that olfactory dysfunction has promise as an early marker of brain pathology and future risk for dementia.

Olfactory Characterization and Training in Older Adults: Protocol Study

The aim of this article is to present the research protocol for a prospective cohort study that will assess the olfactory function and the effect of an intervention based on olfactory training in healthy very old adults (≥75 years old). A convenience sample of 180 older people (50% female) will be recruited in three different environments: hospitalized control group (CH) with stable acute illness (n = 60); ambulatory control group (CA) of community-based living (n = 60); and an experimental odor training group (EOT) from nursing homes (n = 60). The odor training (OT) intervention will last 12 weeks. All the volunteers will be assessed at baseline; CA and EOT groups will also be assessed after 12 weeks. The primary end point will be change in olfactory capacity from baseline to 12 weeks period of intervention or control. The intervention effects will be assessed with the overall score achieved in Sniffin Sticks Test (SST) – Threshold, Discrimination, and Identification (TDI) extended version. Secondary end points will be changes in cognitive tasks, quality of life, mood, immune status, and functional capacity. All these measurements will be complemented with an immune fitness characterization and a deep proteome profiling of the olfactory epithelium (OE) cultured ex vivo. The current study will provide additional evidence to support the implementation of olfactory precision medicine and the development of immunomodulatory nasal therapies based on non-invasive procedures. The proposed intervention will also intend to increase the knowledge about the olfactory function in very elderly people, improve function and quality of life, and promote the recovery of the health.

Olfactory Signatures in the Food Finding Test in Mice With Normal and Alzheimer's Disease-Pathological Aging With Special Concerns on the Effects of Social Isolation

The temporal course and the severity of the involution of sensory systems through aging can be critical since they ensure the ability to perceive and recognize the world. In older people, sensory impairments significantly increase their risk of biological, psychological, and social impoverishment. Besides this, olfactory loss is considered an early biomarker in Alzheimer’s disease (AD) neurodegenerative process. Here we studied olfactory ethograms in middle-aged male and female gold-standard C57BL/6 mice and 3xTg-AD mice, a genetic model of AD that presents cognitive dysfunction and a conspicuous neuropsychiatric-like phenotype. A paradigm involving 1-day food deprivation was used to investigate the ethological patterns shown in the olfactory inspection of a new cage and the sniffing, finding, and eating of hidden food pellets. The sniffing–find–eat temporal patterns were independent of the loss of weight and unveiled (fast) olfactory signatures in Alzheimer’s disease, differing from those (slow progressive) in normal aging. Male 3xTg-AD mice exhibited an early signature than female mice, opposite to animals with normal aging. The sequence of actions was correlated in male and female 3xTg-AD mice in contrast to control mice. Social isolation, naturally occurring in male 3xTg-AD due to the death of cage mates, emphasized their olfactory patterns and disrupted the behavioral correlates. The paradigm provided distinct contextual, sex, and genotype olfactory ethogram signatures useful to investigate olfactory function in normal and AD-pathological aging. Isolation had an impact on enhancing the changes in the olfactory signature here described, for the first time, in the 3xTg-AD model of Alzheimer’s disease.

Olfactory dysfunction in aging and neurodegenerative diseases

Alterations in olfactory functions are proposed to be early biomarkers for neurodegeneration. Many neurodegenerative diseases are age-related, including two of the most common, Parkinson's disease (PD) and Alzheimer's disease (AD). The establishment of biomarkers that promote early risk identification is critical for the implementation of early treatment to postpone or avert pathological development. Olfactory dysfunction (OD) is seen in 90% of early-stage PD patients and 85% of patients with early-stage AD, which makes it an attractive biomarker for early diagnosis of these diseases. Here, we systematically review widely applied smelling tests available for humans as well as olfaction assessments performed in some animal models and the relationships between OD and normal aging, PD, AD, and other conditions. The utility of OD as a biomarker for neurodegenerative disease diagnosis and future research directions are also discussed.

Clinicoradiological features in amyotrophic lateral sclerosis patients with olfactory dysfunction

Objective: Amyotrophic lateral sclerosis (ALS) is an adult-onset neurodegenerative disorder characterized by motor neuron involvement. Although olfactory dysfunction has been described in ALS, clinicoradiological features associated with the olfactory dysfunction remain poorly understood. Methods: We enrolled 30 patients with ALS and age- and sex-matched 53 healthy controls (HCs). All participants underwent the odor stick identification test for Japanese (OSIT-J) and clinical assessments, including disease duration, ALSFRS-R, site of onset, forced vital capacity, and cognitive examinations that reflected the general, executive, memory and language function. We investigated the associations between OSIT-J score and clinical features and examined atrophic changes by voxel-based morphometry (VBM) analysis to MRI. Results: The OSIT-J score was significantly lower in ALS patients than HCs (6.9 ± 3.2 vs. 9.8 ± 1.9, p < 0.001). In ALS, there were significant relationships between OSIT-J score and age at examination, frontal assessment battery, word fluencies, digit span forward, and ADAS-Jcog recognition, but not education, disease type, duration, ALSFRS-R and, %VC. Multiple regression analysis with stepwise method showed the only ADAS-Jcog recognition substantially predicted OSIT-J score. VBM analysis with age, sex, total intracranial volume, and ADAS-Jcog recognition as covariates showed OSIT-J scores were substantially correlated with atrophic changes of left orbital cortex consisting of gyrus rectus and medial orbital gyrus and right hippocampus in ALS. Conclusion: ALS patients could show substantial olfactory dysfunction in association with orbital cortex and hippocampus involvements. The olfactory examination could be a useful marker for screening of frontotemporal alteration in ALS.

Possible Use of Phytochemicals for Recovery from COVID-19-Induced Anosmia and Ageusia

The year 2020 became the year of the outbreak of coronavirus, SARS-CoV-2, which escalated into a worldwide pandemic and continued into 2021. One of the unique symptoms of the SARS-CoV-2 disease, COVID-19, is the loss of chemical senses, i.e., smell and taste. Smell training is one of the methods used in facilitating recovery of the olfactory sense, and it uses essential oils of lemon, rose, clove, and eucalyptus. These essential oils were not selected based on their chemical constituents. Although scientific studies have shown that they improve recovery, there may be better combinations for facilitating recovery. Many phytochemicals have bioactive properties with anti-inflammatory and anti-viral effects. In this review, we describe the chemical compounds with anti- inflammatory and anti-viral effects, and we list the plants that contain these chemical compounds. We expand the review from terpenes to the less volatile flavonoids in order to propose a combination of essential oils and diets that can be used to develop a new taste training method, as there has been no taste training so far. Finally, we discuss the possible use of these in clinical settings.

Handgrip strength as a moderator of the influence of age on olfactory impairment in US adult population ≥ 40 years of age

The aim of this study was to determine whether handgrip strength attenuates the negative relationship between age and olfactory function in a representative US population sample 40 years old and over. A cross-sectional study was performed with 2861 adults from the US National Health and Nutrition Examination Survey NHANES (2013–2014). An 8-item odor identification test was applied to determine olfactory function. Muscle strength was determined through a handgrip dynamometer (defined as the sum of the largest handgrip strength reading from right and left hands). Moderation analysis was performed to test whether the association between age and olfactory impairment was moderated by handgrip strength. Moderation analysis highlighted two regions of significance: the first region was found at < 56.6 kg, indicating that the adverse influence of age on olfactory function may be greater for the participants in this area; the second region was found at ≥ 56.6 kg, indicating that the negative impact of age on olfactory function disappeared for adults who were above this estimate point. In conclusion, handgrip strength, a general indicator of muscle strength, moderates the relationship between age and olfactory ability in a US adult population aged 40 years and older. Our findings are clinically relevant, since they emphasize the importance of muscular fitness in adulthood and old age by diminishing the deleterious effect of aging on olfactory performance.

Six-month smell and taste recovery rates in coronavirus disease 2019 patients: a prospective psychophysical study

BACKGROUND

The long-term recovery rate for coronavirus disease 2019 related chemosensory disturbances has not yet been clarified.

METHODS

Olfactory and gustatory functions were assessed with psychophysical tests in patients in the first seven days from coronavirus disease 2019 onset and one, two, three and six months after the first evaluation.

RESULTS

A total of 300 patients completed the study. The improvement in olfactory function was significant at the two-month follow up. At the end of the observation period, 27 per cent of the patients still experienced a persistent olfactory disturbance, including anosmia in 5 per cent of cases. As for taste, the improvement in the psychophysical scores was significant only between the baseline and the 30-day control. At the 6-month evaluation, 10 per cent of the patients presented with a persistent gustatory disturbance with an incidence of complete ageusia of 1 per cent.

CONCLUSION

Six months after the onset of coronavirus disease 2019, about 6 per cent of patients still had a severe persistent olfactory or gustatory disturbance.

Olfactory impairment in men and mice related to aging and amyloid-induced pathology

Olfaction, or the sense of smell, is one of the most ancient senses in men and mice, important for a large variety of innate and acquired behaviors. Clinical data reveal an early impairment of olfaction during normal aging and in the course of neurodegenerative diseases, but the underlying cellular/molecular mechanisms remain obscure. In the current review, we compare different aspects of the aging- and Alzheimer's disease related impairment of olfaction in men and mice, aiming at the identification of common morbidities and biomarkers, which can be analyzed in detail in the appropriate mouse models. We also identify common, often interdependent (patho)physiological pathways, including but not limited to extracellular amyloid depositions, neuroinflammation, ɛ4 allele of the apolipoprotein E, CNS insulin resistance, and the impairment of adult neurogenesis, to be targeted by basic and clinical research.

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.

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.

The association between olfactory dysfunction and cardiovascular disease and its risk factors in middle-aged and older adults

While previous studies have reported olfactory dysfunction (OD) in relation to cardiovascular disease (CVD), few population-based studies have investigated whether such associations differ by sex. The purpose of this study was to identify the association between CVD and its risk factors with OD, and the sex-associated differences within the general population. We examined 20,016 adults aged 40 and older from the Korean National Health and Nutrition Examination Survey. All subjects reported on their history of OD. CVD and its risk factors included coronary artery disease (CAD), stroke, hypertension, diabetes, obesity, abdominal obesity, and hypertriglyceridemia; logistic regression was used to analyse their associations with OD, and additive interaction was used to analyse the interaction between risk factors and sex. In males, CAD was more likely to be associated with OD (odds ratio [OR] 1.81, 95% confidence interval [CI] 1.05–3.14), whereas abdominal obesity was associated with OD in females (OR 1.39, 95% CI 1.06–1.84).Additive interaction were observed between abdominal obesity and female sex with a relative excess risk of interaction of 0.45 (95% CI 0.26–0.63). Our findings suggest the relationship between OD and CVD and its risk factors and sex-associated differences among middle-aged and older adults.

Olfactory loss and aging: connections with health and well-being

Age-related olfactory dysfunction, or presbyosmia, is a common sensory impairment in aging adults. People in this demographic group with comorbid conditions or exposure to viral, traumatic, or environmental insults remain at the greatest risk for impairment. Several methods for assessing olfaction exist, but they are only available in special settings and require consideration of age, sex, ancestry, and cognition. Perhaps most importantly, olfactory dysfunction has been suggested as an early sign of Alzheimer's and Parkinson's disease and therefore may serve as a tool in the diagnosis and prognosis of these neurodegenerative conditions. Outside of this context, olfactory loss also impacts nutrition, safety, and social relationships, and even predicts mortality itself. This review covers the detection and manifestations of olfactory decline in aging individuals and the myriad ways in which olfactory impairment is connected to their health and well-being.

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.

Olfaction as a Marker for Dystonia: Background, Current State and Directions

Dystonia is a heterogeneous group of hyperkinetic movement disorders. The unifying descriptor of dystonia is the motor manifestation, characterized by continuous or intermittent contractions of muscles that cause abnormal movements and postures. Additionally, there are psychiatric, cognitive, and sensory alterations that are possible or putative non-motor manifestations of dystonia. The pathophysiology of dystonia is incompletely understood. A better understanding of dystonia pathophysiology is highly relevant in the amelioration of significant disability associated with motor and non-motor manifestations of dystonia. Recently, diminished olfaction was found to be a potential non-motor manifestation that may worsen the situation of subjects with dystonia. Yet, this finding may also shed light into dystonia pathophysiology and yield novel treatment options. This article aims to provide background information on dystonia and the current understanding of its pathophysiology, including the key structures involved, namely, the basal ganglia, cerebellum, and sensorimotor cortex. Additionally, involvement of these structures in the chemical senses are reviewed to provide an overview on how olfactory (and gustatory) deficits may occur in dystonia. Finally, we describe the present findings on altered chemical senses in dystonia and discuss directions of research on olfactory dysfunction as a marker in dystonia.