Olfactory function in Wave 2 of the National Social Life, Health, and Aging Project

Examining the Longitudinal Relationship Between Olfactory Dysfunction and Frailty in Community-Dwelling, older US Adults

OBJECTIVE

Olfactory dysfunction is a "canary in the coalmine" for aging conditions. We evaluated olfactory dysfunction as a biomarker of early frailty in older adults living in the United States.

STUDY DESIGN

Prospective, longitudinal, nationally representative study.

SETTING

National Social Life, Health and Aging Project (NSHAP).

METHODS

We examined data from 1061 community-dwelling older US adults. Odor identification (5-item Sniffin' Stick) and frailty scores were measured at baseline and 5-year follow-up. Multivariate logistic regressions evaluated the association between olfactory dysfunction and frailty at baseline in cross-section and over time in the transition from robust to prefrail to frail, adjusting for confounding factors measured at baseline.

RESULTS

Older US adults who were anosmic at baseline were more likely to be frail 5 years later compared to normosmic peers (odds ratio [OR]: 3.83, 95% confidence interval [CI]: 1.10-13.31, P = .035). Examining changes in frailty stage over time, we found that anosmics were more likely to transition from prefrail to frail over 5 years (OR: 3.25, 95% CI: 1.31-8.08, P = .011). Interestingly, hyposmics did not show a similar trajectory toward frailty (P > .05). In contrast, olfactory dysfunction was not associated with frailty in cross-section (OR: 0.90, 95% CI: 0.43-1.89, P = .787, hyposmia; OR: 0.72, 95% CI: 0.15-3.35, P = .673, anosmia).

CONCLUSION

Older US adults with anosmia face higher odds of becoming frail over 5 years, especially those in the prefrail stage. Olfactory dysfunction may serve as a surrogate marker for early-stage neurodegenerative diseases, which are strong contributors to frailty.

Olfactory decline develops in parallel with frailty in older US adults with obstructive lung diseases

BACKGROUND

Frailty is prevalent among older adults with asthma or chronic obstructive pulmonary disease (obstructive lung diseases [OLDs]). Frailty and OLD's co-occurrence is associated with increased hospitalization/mortality. Chemosensory dysfunction is closely connected to both OLD and frailty. We evaluated the utility of olfactory decline as a biomarker of frailty in the setting of OLD.

METHODS

We performed a prospective, longitudinal, nationally representative study of community-dwelling older US adults in the National Social Life, Health and Aging Project, an omnibus in-home survey. Respondents reported a physician's diagnosis of OLD. Decline in odor identification and sensitivity over 5 years and frailty (adapted fried frailty phenotype criteria) were measured using standard tools. Multivariate logistic regressions evaluated the association between OLD status, olfactory decline, and frailty.

RESULTS

We compared individuals with OLD (n = 98; mean age 71.2 years, 59.2% women) and those without OLD (n = 1036; mean age 69.5 years, 58.9% women). Olfactory identification decline was associated with developing frailty over the 5-year follow-up period in individuals with OLD (odds ratio [OR] = 9.1, 95% confidence interval [CI] = 2.1-38.6, p = 0.003). Olfactory decline predicted incidence of frailty in individuals with OLD (identification: OR = 4.8, 95% CI = 1.3-17.5, P = 0.018; sensitivity: OR = 6.1, 95%CI = 1.2-31.0, p = 0.030) but not in those without OLD adjusting for demographics, heavy alcohol use, current smoking, and comorbidity. Results were robust to different thresholds for olfactory decline and frailty development.

CONCLUSIONS

Older adults with OLD who experience olfactory decline face higher odds of developing frailty. Use of olfactory decline as a biomarker to identify frailty could allow earlier intervention and decrease adverse outcomes for high-risk older adults with OLD.

Experiences of living without a sense of smell: Like "Being Behind Glass"

This study addresses the paucity of research concerning the subjective experiences of those affected by anosmia. In the study, we interviewed individuals(n = 11) recruited via the charity (Fifth Sense) and used Interpretative Phenomenological Analysis (IPA) to analyse the data. Findings revealed three main themes and seven sub themes. The main themes are Living with Anosmia; Remembrance of things old and new and Resilience. The study reveals the process of becoming aware of being anosmic and the relationships with others in this process including potentially unhelpful minimisations of the impact by professionals. In addition to a sense of isolation and insecurity, living with anosmia for some participants brought with it an identification of being 'anosmic' and feeling part of a community. This was in contrast to a general lack of public knowledge and understanding of anosmia. The findings of the study demonstrated the importance of smell to time, place and relationship and the recalling of smells as bringing a sense of connectivity to loved ones, of times past and also a sense of loss of ability. Participants also described the ways in which they coped and adapted to a life with anosmia and focused on positive aspects of life. These findings provide a rich qualitative account of the experience of anosmia. The findings point towards future research which could inform us about the lives of those who are anosmic and currently unaware and of those recently diagnosed, which will create a richer understanding of the experiences of anosmia.

Normative data for the Vietnamese smell identification test

Introduction

The 12-item Vietnamese smell identification test (VSIT) has been developed to evaluate the olfactory function of the Vietnamese population. This study aimed to investigate the normative value of the VSIT in different age groups and sexes.

Methods

This cross-sectional study was conducted at Ho Chi Minh University Medical Center, Vietnam. All participants were evaluated for odor identification ability using the VSIT. We included healthy participants aged 18 years or older with no history of olfactory disturbances.

Results

A total of 391 healthy volunteers were recruited with a mean age of 45.80 years (SD: 17.62; range: 18-86; female: 63.4 %). The tenth percentile of scores on the 0-12 VSIT scale was 8.3 in participants aged 18-29 years, 9.0 in 30-39 years, 8.0 in 40-49 years, 7.8 in 50-59 years, 7.9 in 60-69 years and 6.0 in over 70 years. Young adults (18-39 years old) had better olfactory identification ability than older adults (over 50 years), p < 0.001. There was a significant main effect of sex on VSIT score (p = 0.02), suggesting that females outperformed males. Sensitivity to 8 odors were negatively correlated with age: lemon, garlic, banana, coffee, mango, guava, apple and watermelon (p < 0.05 in all cases) whereas four odors were age-independent including orange, fish sauce, soy sauce, and fish.

Conclusion

Normative data provide guidance for assessing individual olfactory function. However, there were significant sex and age effects on olfactory identification scores on the VSIT. Therefore, future studies should be conducted to better adjust for those confounders mentioned above.

Association of APOE ε4 Status With Long-term Declines in Odor Sensitivity, Odor Identification, and Cognition in Older US Adults

BACKGROUND AND OBJECTIVES

The APOE ε4 allele confers susceptibility to faster decline in odor identification and subsequently to Alzheimer disease (AD). Odor identification requires recognizing and naming odors and detecting them (odor sensitivity). Whether APOE ε4 is associated with decline of odor sensitivity and whether such decline serves as a harbinger of cognitive decline and AD remains unclear. We determined whether and when APOE ε4 affects decline in odor sensitivity, odor identification, and cognition in the National Social Life Health and Aging Project (NSHAP).

METHODS

We used data from NSHAP, a nationally representative survey study of home-dwelling US older adults. Olfaction was measured over time (odor identification in 2005, 2010, and 2015; odor sensitivity in 2010 and 2015; both using validated tests). Cognition was measured with a modified version of the Montreal Cognitive Assessment in 2010 and 2015. Genotyping was performed using DNA samples collected in 2010. Odor sensitivity and identification were compared among APOE ε4 carriers and noncarriers stratified by age. Relationships between APOE ε4, odor sensitivity, odor identification, and cognition were analyzed in cross-section using ordinal logistic regression and longitudinally using mixed-effects models adjusted for confounders.

RESULTS

Odor sensitivity was measured in 865 respondents, odor identification in 1,156 respondents, and cognition in 864 respondents; all these respondents had genetic data available. Odor sensitivity deficits in APOE ε4 carriers were apparent at ages 65-69 years, whereas odor identification deficits did not appear until ages 75-79 years. Subsequently, odor sensitivity did not decline more rapidly with aging in APOE ε4 carriers compared with that in noncarriers (carrier status and aging interaction: odds ratio [OR] 1.44, 95% CI 0.94-2.19, p = 0.092), whereas odor identification declined more rapidly in carriers (aging 10 years interaction: OR 0.26, 95% CI 0.13-0.52, p < 0.001). As expected, and in parallel to odor identification, cognition declined more rapidly in APOE ε4 carriers (interaction: OR 0.55, 95% CI 0.34-0.89, p = 0.015).

DISCUSSION

APOE ε4 affects decline of odor sensitivity earlier than odor identification or cognition. Thus, testing odor sensitivity may be useful to predict future impaired cognitive function. Identifying the mechanism underlying these relationships will elucidate the key role of olfaction in neurodegeneration during aging.

Olfactory Function and Olfactory Disorders

The sense of smell is important. This became especially clear to patients with infection-related olfactory loss during the SARS-CoV-2 pandemic. We react, for example, to the body odors of other humans. The sense of smell warns us of danger, and it allows us to perceive flavors when eating and drinking. In essence, this means quality of life. Therefore, anosmia must be taken seriously. Although olfactory receptor neurons are characterized by regenerative capacity, anosmia is relatively common with about 5 % of anosmic people in the general population. Olfactory disorders are classified according to their causes (e. g., infections of the upper respiratory tract, traumatic brain injury, chronic rhinosinusitis, age) with the resulting different therapeutic options and prognoses. Thorough history taking is therefore important. A wide variety of tools are available for diagnosis, ranging from short screening tests and detailed multidimensional test procedures to electrophysiological and imaging methods. Thus, quantitative olfactory disorders are easily assessable and traceable. For qualitative olfactory disorders such as parosmia, however, no objectifying diagnostic procedures are currently available. Therapeutic options for olfactory disorders are limited. Nevertheless, there are effective options consisting of olfactory training as well as various additive drug therapies. The consultation and the competent discussion with the patients are of major importance.

Development and validation of the Olfactory Memory Test Battery (OMTB) based on odors with high- and low-verbalizability

BACKGROUND

Odor memory is an important field of clinical research for its distinctive characteristics, which differ from those of other sensory systems. To date, several tests have been implemented for the assessment of odor memory. Despite a range of studies demonstrating the importance of verbal mediation in odor memory, few have distinguished odor memory performance in different odor verbalization levels.

NEW METHOD

We aimed to develop a standardized odor memory test toolbox with one group of odors that are easily verbally identified and the other group of odors that are difficult to identify. The test contained two odor categories (high- and low-verbalizability odors), each consisting of three subtests (short- and long-term memory and working memory).

RESULTS

Satisfactory test-retest reliability and solid validity of the odor recognition and working memory test were shown in both odor categories. Moreover, people scored significantly better with high- than low-verbalizability odors. A negative age effect on odor memory performance was also found.

COMPARISON WITH EXISTING METHODS

No previous odor memory test distinguished odor memory performance in different odor verbalization levels, while the Olfactory Memory Test Battery (OMTB) contains high- and low-verbalizability odors and each category has three subtests.

CONCLUSIONS

The present study indicated the OMTB is a comprehensive assessment of odor memory with good reliability and validity. All subtests can be used separately or in combination with each other according to the clinical and research needs.

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.

Androstadienone sensitivity is associated with attention to emotions, social interactions, and sexual behavior in older U.S. adults

Δ 4,16-androstadien-3-one (androstadienone) is a putative human pheromone often linked to sexual attraction in young adults, although specific associations with sexual behavior are not yet established. Androstadienone also serves a broader social-emotional function beyond the sexual domain, specifically tuning the brain to efficiently process emotional information. Whether these effects persist throughout the lifespan into post-reproductive life is unknown. In a laboratory study of older adults, those with greater androstadienone odor sensitivity paid greater attention to subliminal emotional information, specifically, angry faces (p = 0.05), with a similar relationship to happy faces. In contrast, the physical odor n-butanol (a control) did not affect emotional attention (p = 0.49). We then extended this laboratory research and determined whether sensitivity to androstadienone affects the everyday lives of older adults by measuring their social and sexual behavior. In this second study, we surveyed in a nationally representative sample of US older adults living in their homes (National Social Life and Aging Project, 62-90 years; n = 2,086), along with their sensitivity to androstadienone, general olfactory function, health and demographics. Greater sensitivity to androstadienone was associated with richer social lives: having more friends, increased communication with close friends and family, and more participation in organized social events and volunteer activities (all p's ≤ 0.05, generalized linear models, adjusted for age and gender). It was also associated with more recent sexual activity, more frequent sexual thoughts, and viewing sex as an important part of life (all p's ≤ 0.05). General olfactory function did not explain these associations, supporting a specialized function for this pheromone during everyday life, and expanding its role to social life as well as sexual behavior, likely mediated by enhanced attention to emotional information.

Olfactory Sensitivity Is Associated with Body Mass Index and Polymorphism in the Voltage-Gated Potassium Channels Kv1.3

Smell strongly contributes to food choice and its hedonistic evaluation. A reduction or loss of smell has been related to malnutrition problems, resulting in excessive weight loss or gain. Voltage-gated potassium channels Kv1.3 are widely expressed in the olfactory bulb, and contribute mainly to the value of the resting membrane potential and to the frequency of action potentials. Mutations in the Kv1.3 gene are associated with alterations in glycemic homeostasis and olfactory sensitivity. We evaluated the olfactory performance in 102 healthy subjects and its association with BMI and polymorphism in the human Kv1.3 gene. Olfactory performance, based on the olfactory threshold, discrimination and identification scores and their summed score (TDI), was measured using the “Sniffin’ Sticks” test. Subjects were genotyped for the rs2821557 polymorphism of the Kv1.3 gene, whose major allele T was associated with a super-smeller phenotype, lower plasma glucose levels and resistance to diet-induced obesity as compared with the minor allele C. Based on the Kv1.3 genotype, the TDI and I olfactory scores obtained by the subjects were the following: TT > TC > CC. Subjects who were TT homozygous or heterozygous exhibited lower BMIs and reached higher olfactory scores than those with the CC genotype. The results were sex-dependent: heterozygous females performed better than heterozygous males. These findings show an inverse relationship between olfactory function and BMI, and a significant effect of the Kv1.3 genotypes on the olfactory functions and on the BMIs of the subjects. Finally, they suggest that the sex-related differences in the olfactory function can be partially ascribed to the Kv1.3 gene’s polymorphism.

Psychophysical Testing in Chemosensory Disorders

Purpose of Review

To provide an overview of psychophysical testing in olfaction and gustation.

Recent Findings

Subjective patient report correlates poorly with objective assessment of olfaction and gustation. It is therefore important that clinicians and researchers perform psychophysical testing during chemosensory assessment. There are several validated psychophysical tests of olfaction and gustation, with ongoing developments accelerated by the COVID-19 pandemic. These tests have been culturally and linguistically adapted globally. Screening tests have been developed with careful consideration to distinguish normosmics from those with olfactory dysfunction.

Summary

Validated chemosensory tools are available for use by the clinician to support screening, diagnosis, or monitoring. There are promising advances in self-assessment and screening that provide avenues for the development of a standardised pathway for identification and formal assessment of patients with smell and taste disorders.

Could melatonin have a potential adjuvant role in the treatment of the lasting anosmia associated with COVID-19? A review

INTRODUCTION

Anosmia, the loss of the sense of smell, is usually associated with rhinopathies and has been reported as a common symptom of COVID-19. There is no specific drug to treat this condition, although some evidence suggests that melatonin could promote the recovery of olfactory sensory neurons.

METHODS

We set out to perform a narrative review to synthesize the current evidence in this area in respect of our hypothesis that melatonin may be linked with anosmia and play a part in oxidative stress and the regulation of inflammation. The main electronic databases (MEDLINE/PubMed, Embase, and Cochrane) were searched.

RESULTS

The search produced 26 articles related to our hypothesis. Some studies examined issues related to melatonin's effects and its use as adjuvant therapy for COVID-19. Despite some studies suggesting that melatonin may have potential in the treatment of COVID-19, to the best of our knowledge, there have been no trials that have used it to treat anosmia associated with the disease. Few articles identified proposed that melatonin might have an effect on olfactory cells.

DISCUSSION

Further experimental and clinical research on the role of circadian melatonin in the olfactory system is warranted. This will provide evidence of the use of melatonin in the management of anosmia. A number of identified studies suggest that the imbalanced release of melatonin by the pineal gland associated with sleep disturbance may play a role in anosmia, although the specific pathway is not yet entirely clear. This may be a base for further research into the potential role of melatonin as adjuvant treatment of anosmia.

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.

Olfactory dysfunction is associated with cognitive impairment in patients with obstructive sleep apnea: a cross-sectional study

PURPOSE

Obstructive sleep apnea (OSA) increases the risk for olfactory dysfunction. However, the relationship between olfactory function and cognition in OSA patients is unclear. The present study aimed to investigate the relationship between cognition and olfactory dysfunction (OD) in patients with OSA.

METHOD

This was a cross-sectional study in which 74 patients with OSA and 22 controls were recruited. All subjects completed polysomnography, Sniffin' Sticks, and -neurocognitive assessments. According to results of Sniffin' Sticks, OSA patients were divided into two groups: OSA with OD (53 cases) and OSA without OD (21 cases). Neurocognitive function was assessed by Montreal Cognitive Assessment (MoCA), Memory and Executive Screening (MES), and Shape Trail Test (STT). Cognition was compared between OSA with and without OD. Correlation between olfactory parameters and respiratory sleep parameters and neurocognitive assessments was analyzed.

RESULTS

Compared with OSA without OD, OSA with OD showed significantly decreased neurocognitive scores of MoCA (29-27 vs 27-23, p < 0.01), MES-5R (45-40.1 vs 43-33.5, p < 0.01) and increased consuming time of STT-B (91.66 vs 121.63, p < 0.01). A positive correlation was found between the scores of MoCA and MES-5R and all olfactory parameters. In addition, a negative correlation was present between the time consumed for STT-B and odor thresholds (r = - 0.344, p < 0.01), odor identification (r = - 0.335, p < 0.01), and threshold-discrimination-identification scores (r = - 0.448, p < 0.01).

CONCLUSION

Olfactory function is associated cognitive function in patients with OSA and may provide a new direction for early treatment interventions in OSA patients at risk for cognitive impairment.

Restoration of olfactory dysfunctions by nanomaterials and stem cells-based therapies: Current status and future perspectives

Dysfunction in the olfactory system of a person can have adverse effects on their health and quality of life. It can even increase mortality among individuals. Olfactory dysfunction is related to many factors, including post-viral upper respiratory infection, head trauma, and neurodegenerative disorders. Although some clinical therapies such as steroids and olfactory training are already available, their effectiveness is limited and controversial. Recent research in the field of therapeutic nanoparticles and stem cells has shown the regeneration of dysfunctional olfactory systems. Thus, we are motivated to highlight these regenerative approaches. For this, we first introduce the anatomical characteristics of the olfactory pathway, then detail various pathological factors related to olfactory dysfunctions and current treatments, and then finally discuss the recent regenerative endeavors, with particular focus on nanoparticle-based drug delivery systems and stem cells. This review offers insights into the development of future therapeutic approaches to restore and regenerate dysfunctional olfactory systems.

Food Neophobia, Odor and Taste Sensitivity, and Overall Flavor Perception in Food

Smell, which allows us to gather information about the hedonic value of an odor, is affected by many factors. This study aimed to assess the relationship among individual factors, odor sensitivity, and enjoyment, and to evaluate how overall flavor perception and liking in actual food samples are affected by odor sensitivity. A total of 749 subjects, from four different Italian regions, participated in the study. The olfactory capabilities test on four odors (anise, banana, mint, and pine), as well as PROP (6-n-prpyl-2-thiouracil) status and food neophobia were assessed. The subjects were clustered into three groups of odor sensitivity, based on the perceived intensity of anise. The liking and intensity of the overall flavor were evaluated for four chocolate puddings with increasing sweetness (C1, C2, C3, and C4). The individual variables significantly affected the perceived intensity and liking of the odors. Even if all of the odor sensitivity groups perceived the more intensely flavored samples as the C1 and C4 chocolate puddings, the high-sensitivity group scored the global flavor of all of the samples as more intense than the low-sensitivity group. The low-sensitive subjects evaluated the liking of the sweeter samples with higher scores than the moderate-sensitive subjects, whereas the high-sensitive subjects gave intermediate scores. In conclusion, odor sensitivity plays a pivotal role in the perception and liking of real food products; this has to be taken into account in the formulation of new products, suitable for particular categories with reduced olfactory abilities.

Olfactory Decline in Older Adults with Mild Cognitive Impairment with and without Comorbidities

Over the past two decades, several studies have measured olfactory performance in Mild Cognitive Impairment (MCI). Deficits are observed in multiple olfactory domains, including odour detection threshold, identification, discrimination, and memory. In this study, the psychophysiological Sniffin’ Sticks smell screening test was administered to examine olfactory functioning in 145 older adults with MCI, a group with MCI and chronic comorbid conditions, and a healthy age-matched comparison group. We hypothesised that olfactory performance will deteriorate in the two MCI groups compared to the control group, even after assessing the known contributions of age and gender. The higher olfactory deterioration in the group with the MCI and the comorbidities in the first year disappeared in the second. This could mean that early consideration of the potential effect of other comorbidities that might affect olfaction should be taken and addressed, as they could easily mask the effect of cognitive decline and/or contribute to it. This study also found higher deterioration in smell identification in participants with MCI, as has been found repeatedly in similar research. Olfactory identification seems to be a more robust marker for discriminating people with MCI and without, and even discriminating between those with MCI and having other health problems.

Sleep-Disordered Breathing Is Associated With Impaired Odor Identification in Older U.S. Adults

BACKGROUND

Sleep-disordered breathing (SDB) is a common, underdiagnosed condition in older adults with major health consequences, including disrupted central nervous system functioning. Whether SDB may affect sensory function is unclear. We sought to address this question by comparing 2 forms of olfactory testing which measure peripheral and central olfactory processing.

METHODS

We assessed SDB (survey-reported snoring frequency, nighttime apneic events, or diagnosis of sleep apnea) in the National Social Life, Health, and Aging Project, a nationally representative sample of older U.S. adults. Odor sensitivity (peripheral) and odor identification (central) were assessed with validated instruments. Logistic regression was used to test the relationship between SDB and olfaction, accounting for relevant covariates, including demographics, cognition, and comorbidity.

RESULTS

Twenty-nine percent of older U.S. adults reported symptoms of SDB (apneic events or nightly snoring). Of these, only 32% had been diagnosed with sleep apnea. Older adults with SDB (those who reported symptoms or have been diagnosed with sleep apnea) were significantly more likely to have impaired odor identification (odds ratio 2.13, 95% confidence interval 1.19-3.83, p = .012) in analyses that accounted for age, gender, race/ethnicity, education, cognition, comorbidities (including depression), and body mass index. Presence of SDB was not associated with impaired odor sensitivity (odds ratio 1.03, 95% confidence interval 0.75-1.43, p = .84).

CONCLUSION

SDB is highly prevalent but underdiagnosed in older U.S. adults and is associated with impaired odor identification but not odor sensitivity. These data support the concept that SDB affects pathways in the central nervous system which involve chemosensory processing.

Odor Sensitivity Versus Odor Identification in Older US Adults: Associations With Cognition, Age, Gender, and Race

The ability to identify odors predicts morbidity, mortality, and quality of life. It varies by age, gender, and race and is used in the vast majority of survey and clinical literature. However, odor identification relies heavily on cognition. Other facets of olfaction, such as odor sensitivity, have a smaller cognitive component. Whether odor sensitivity also varies by these factors has not been definitively answered. We analyzed data from the National Social Life, Health, and Aging Project, a nationally representative study of older US adults (n = 2081). Odor identification was measured using 5 validated odors presented with Sniffin' Stick pens as was odor sensitivity in a 6-dilution n-butanol constant stimuli detection test. Multivariate ordinal logistic regression modeled relationships between olfaction and age, gender, race, cognition, education, socioeconomic status, social network characteristics, and physical and mental health. Odor sensitivity was worse in older adults (P < 0.01), without gender (P = 0.56) or race (P = 0.79) differences. Odor identification was also worse in older adults, particularly men (both P ≤ 0.01), without differences by race. Decreased cognitive function was associated with worse odor identification (P ≤ 0.01) but this relationship was weaker for odor sensitivity (P = 0.02) in analyses that adjusted for other covariates. Odor sensitivity was less strongly correlated with cognitive ability than odor identification, confirming that it may be a more specific measure of peripheral olfactory processing. Investigators interested in associations between olfaction and health should consider both odor sensitivity and identification when attempting to understand underlying neurosensory mechanisms.

Olfaction and Aging: A Review of the Current State of Research and Future Directions

Olfaction, the sense of smell, is characterized by a notable age-dependency such that aging individuals are more likely to have poor olfactory abilities. These impairments are considered to be mostly irreversible and as having potentially profound effects on quality of life and food behavior, as well as constituting warning signs of mortality, cognitive dysfunction, and dementia. Here, we review the current state of research on aging and olfaction, focusing on five topics which we regard to be of particular relevance for the field: nutrition and health, cognition and dementia, mortality, environment and genetics, and training-based enhancement. Under each of these headlines, we provide a state-of-the-art overview and discuss gaps in our knowledge which might be filled by further research. Understanding how olfactory abilities are diminished in aging, and how they may be alleviated or recovered, involves a set of challenging tasks for researchers in the years to come.

Clinical assessment of olfactory function

Approximately 5% of the general population is affected by functional anosmia with approximately additional 15% exhibiting decreased olfactory function. Many of these individuals ask for help. Because the subjective rating of olfactory function is biased, assessment of olfactory function is important. Olfactory measurements are needed for patient counseling and the tracking of changes in the sense of smell over time. The present review provides an overview of frequently used psychophysical tests for olfactory function, discusses differences between threshold and suprathreshold aspects of olfactory function, and gives examples on how to apply psychophysical tests.

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.

IL-1Rahigh-IL-4low-IL-13low: A Novel Plasma Cytokine Signature Associated with Olfactory Dysfunction in Older US Adults

Inflammation has been implicated in physical frailty, but its role in sensory impairment is unclear. Given that olfactory impairment predicts dementia and mortality, determining the role of the immune system in olfactory dysfunction would provide insights mechanisms of neurosensory decline. We analyzed data from the National Social Life, Health and Aging Project, a representative sample of home-dwelling older US adults. Plasma levels of 18 cytokines were measured using standard protocols (Luminex xMAP). Olfactory function was assessed with validated tools (n-butanol sensitivity and odor identification, each via Sniffin' Sticks). We tested the association between cytokine profiles and olfactory function using multivariate ordinal logistic regression, adjusting for age, gender, race/ethnicity, education level, cognitive function, smoking status, and comorbidity. Older adults with the IL-1Rahigh-IL-4low-IL-13low cytokine profile had worse n-butanol odor sensitivity (odds ratio [OR] = 1.61, 95% confidence interval [CI] 1.19-2.17) and worse odor identification (OR = 1.42, 95% CI 1.11-1.80). Proinflammatory, Th1, or Th2 cytokine profiles were not associated with olfactory function. Moreover, accounting for physical frailty did not alter the main findings. In conclusion, we identified a plasma cytokine signature-IL-1Rahigh-IL-4low-IL-13low-that is associated with olfactory dysfunction in older US adults. These data implicate systemic inflammation in age-related olfactory dysfunction and support a role for immune mechanisms in this process, a concept that warrants additional scrutiny.

Cranial Nerve Stimulation for Olfaction (Cranial Nerve 1)

Like sensory maps in other systems, the sense of smell has an organizational structure based on converging projections of olfactory receptor neurons containing unique odorant receptors onto the olfactory bulb in synaptic aggregations termed glomeruli. This organizational structure provides the potential for electrical stimulation and restoration of smell. Prior animal and human studies support the feasibility of an olfactory stimulation device, encouraging ongoing work in development of olfactory implants.

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.

Sex Differences in Human Olfaction: A Meta-Analysis

Although the view that women's olfactory abilities outperform men's is taken for granted, some studies involving large samples suggested that male and female olfactory abilities are actually similar. To address this discrepancy, we conducted a meta-analysis of existing studies on olfaction, targeting possible sex differences. The analyzed sample comprised n = 8 848 (5 065 women and 3 783 men) for olfactory threshold (as measured with the Sniffin Sticks Test; SST), n = 8 067 (4 496 women and 3 571 men) for discrimination (SST), n = 13 670 (7 501 women and 6 169 men) for identification (SST), and a total sample of n = 7 154 (3 866 women and 3 288 men) for works using University of Pennsylvania Smell Identification Test (UPSIT). We conducted separate meta-analyses for each aspect of olfaction: identification, discrimination and threshold. The results of our meta-analysis indicate that women generally outperform men in olfactory abilities. What is more, they do so in every aspect of olfaction analyzed in the current study. However, the effect sizes were weak and ranged between g = 0.08 and g = 0.30. We discuss our findings in the context of factors that potentially shape sex differences in olfaction. Nevertheless, although our findings seem to confirm the "common knowledge" on female olfactory superiority, it needs to be emphasized that the effect sizes we observed were notably small.

Early Aging Effect on the Function of the Human Central Olfactory System

During normal aging process, the smell function declines significantly, starting from the sixth decade of age. While it has been shown that activity in the central olfactory system of seniors responding to odor stimulation is significantly less than that of young people, no information of the aging effect on the functions of this system during normal adulthood and early aging has been gathered. In this study, we used functional magnetic resonance imaging to investigate the olfaction-related brain activity in the central olfactory structures of 43 healthy adult volunteers aged from 22 to 64 years. The participants' smell identification function was negatively correlated with age (r = -.32, p = .037). Significant negative correlation was observed between age and the olfaction-related activities in the bilateral dorsolateral prefrontal cortex, left insular cortex, and left orbitofrontal cortex (p < .001, corrected with cluster size ≥28 voxels). There was no significant correlation observed between age and the activity in the primary olfactory cortex detected in this age group. These results suggest that age-related functional decline in the human brain is more prominent in the secondary and higher-order central olfactory structures than the primary olfactory cortex in the early aging process.

Anosmia-A Clinical Review

Anosmia and hyposmia, the inability or decreased ability to smell, is estimated to afflict 3-20% of the population. Risk of olfactory dysfunction increases with old age and may also result from chronic sinonasal diseases, severe head trauma, and upper respiratory infections, or neurodegenerative diseases. These disorders impair the ability to sense warning odors in foods and the environment, as well as hinder the quality of life related to social interactions, eating, and feelings of well-being. This article reports and extends on a clinical update commencing at the 2016 Association for Chemoreception Sciences annual meeting. Included were reports from: a patient perspective on losing the sense of smell with information on Fifth Sense, a nonprofit advocacy organization for patients with olfactory disorders; an otolaryngologist's review of clinical evaluation, diagnosis, and management/treatment of anosmia; and researchers' review of recent advances in potential anosmia treatments from fundamental science, in animal, cellular, or genetic models. As limited evidence-based treatments exist for anosmia, dissemination of information on anosmia-related health risks is needed. This could include feasible and useful screening measures for olfactory dysfunction, appropriate clinical evaluation, and patient counseling to avoid harm as well as manage health and quality of life with anosmia.

The Prevalence of Anosmia and Associated Factors Among U.S. Black and White Older Adults

BACKGROUND

Olfactory impairment is common among older adults; however, data are largely limited to whites.

METHODS

We conducted pooled analyses of two community-based studies: the Atherosclerosis Risk in Communities study (ARIC, 1,398 blacks and 4,665 whites), and the Health, Aging, and Body Composition study (Health ABC, 958 blacks and 1,536 whites) to determine the prevalence of anosmia and associated factors for black and white older adults in the United States.

RESULTS

The overall prevalence of anosmia was 22.3% among blacks and 10.4% among whites. Blacks had a markedly higher odds of anosmia compared to whites in age and sex adjusted analyses (odds ratio [OR] 2.96, 95% confidence interval [CI] = 2.59-3.38). In both blacks and whites, higher anosmia prevalence was associated with older age and male sex. The highest prevalence was found in black men 85 years or older (58.3%), and the lowest in white women aged 65-69 years (2.4%). Higher education level, lower cognitive score, ApoE ε4, daytime sleepiness, poorer general health status, lower body mass index, and Parkinson disease were associated with higher prevalence of anosmia in one or both races. However, the racial difference in anosmia remained statistically significant after adjusting for these factors (fully adjusted OR = 1.76, 95%CI: 1.50-2.07). Results were comparable between the two cohorts.

DISCUSSION

Anosmia is common in older adults, particularly among blacks. Further studies are needed to identify risk factors for anosmia and to investigate racial disparities in this sensory deficit.

Sleep and Olfaction among Older Adults

BACKGROUND

Sleep and olfaction are both critical physiological processes that tend to worsen with age. Decline in olfaction can be an early indicator of neurodegenerative diseases, whereas poor sleep quality is associated with reduced physical and mental health. Given associations with aging-related health declines, we explored whether variations in sleep were associated with olfactory function among older adults.

METHODS

We assessed the relationship between sleep characteristics and olfaction among 354 community-dwelling older adults. Olfaction was measured using a validated field and survey research tool. Sleep characteristics were measured using wrist actigraphy and with self-report of sleep problems. We fit structural equation models of latent constructs of olfaction based on olfactory task items and let this be a function of each sleep characteristic.

RESULTS

Actigraph sleep quality measures were associated with odor identification, but not with odor sensitivity. Longer duration sleepers had worse odor sensitivity compared to medium (58 h) sleepers, but sleep duration was not associated with odor identification. Reported sleep problems and reported usual duration were not associated with olfaction.

CONCLUSIONS

Diminished sleep quality was associated with reduced capacity to identify odors. Determining whether this is a causal association will require further study and longitudinal data.

Different patterns of age-related central olfactory decline in men and women as quantified by olfactory fMRI

Age-related olfactory decline, or presbyosmia, is a prevalent condition with potentially devastating consequences on both quality of life and safety. Despite clear evidence for this decline, it is unknown whether presbyosmia is sex-dependent and also whether it is due to central or peripheral olfactory system deterioration. Therefore, the goals of this study were to investigate the neurofunctional substrate of olfactory decline and examine its relationship to age and sex in thirty-seven (18 women, 19 men) healthy older participants using olfactory functional MRI (fMRI). The olfactory fMRI paradigm utilized unique odor+visual and visual-only conditions to contrast peripheral-to-central and central-to-central olfactory processing, respectively. Age was negatively correlated with fMRI activation in olfactory-related regions. Significant aging effects were identifiable in male participants in all target regions. Female participants, however, showed a different pattern of functional decline. Extended unified structural equation modeling (euSEM) analysis revealed that the effective functional connectivity profile was drastically different between male and female participants, with females manifesting a top-down mechanism to offset age-related olfactory activation decline. Our results support the hypotheses that the central olfactory system is involved in age-related olfactory decline, and that resilience to age-related olfactory decline in women may be due to their profuse olfactory network effective connectivity.

What Makes a Better Smeller?

Olfaction is often viewed as difficult, yet the empirical evidence suggests a different picture. A closer look shows people around the world differ in their ability to detect, discriminate, and name odors. This gives rise to the question of what influences our ability to smell. Instead of focusing on olfactory deficiencies, this review presents a positive perspective by focusing on factors that make someone a better smeller. We consider three driving forces in improving olfactory ability: one’s biological makeup, one’s experience, and the environment. For each factor, we consider aspects proposed to improve odor perception and critically examine the evidence; as well as introducing lesser discussed areas. In terms of biology, there are cases of neurodiversity, such as olfactory synesthesia, that serve to enhance olfactory ability. Our lifetime experience, be it typical development or unique training experience, can also modify the trajectory of olfaction. Finally, our odor environment, in terms of ambient odor or culinary traditions, can influence odor perception too. Rather than highlighting the weaknesses of olfaction, we emphasize routes to harnessing our olfactory potential.

Odor detection thresholds in a population of older adults

OBJECTIVES/HYPOTHESIS

To measure odor detection thresholds and associated nasal and behavioral factors in an older adult population.

STUDY DESIGN

Cross-sectional cohort study.

METHODS

Odor detection thresholds were obtained using an automated olfactometer on 832 participants, aged 68 to 99 (mean age = 77) years in the 21-year (2013-2016) follow-up visit of the Epidemiology of Hearing Loss Study.

RESULTS

The mean odor detection threshold (ODT) score was 8.2 (range = 1-13; standard deviation = 2.54), corresponding to an n-butanol concentration of slightly less than 0.03%. Older participants were significantly more likely to have lower (worse) ODT scores than younger participants (P < .001). There were no significant differences in mean ODT scores between men and women. Older age was significantly associated with worse performance in multivariable regression models, and exercising at least once per week was associated with reduced odds of having a low (≤5) ODT score. Cognitive impairment was also associated with poor performance, whereas a history of allergies or a deviated septum was associated with better performance.

CONCLUSIONS

Odor detection threshold scores were worse in older age groups but similar between men and women in this large population of older adults. Regular exercise was associated with better odor detection thresholds, adding to the evidence that decline in olfactory function with age may be partly preventable.

LEVEL OF EVIDENCE

3b. Laryngoscope, 127:1257-1262, 2017.

Nitrogen dioxide pollution exposure is associated with olfactory dysfunction in older U.S. adults

BACKGROUND

Olfactory dysfunction has profound effects on quality of life, physical and social function, and mortality itself. Nitrogen dioxide (NO2 ) is a pervasive air pollutant that is associated with respiratory diseases. Given the olfactory nerve's anatomic exposure to airborne pollutants, we investigated the relationship between NO2 exposure and olfactory dysfunction.

METHODS

The ability to identify odors was evaluated using a validated test in respondents from the National Social Life, Health, and Aging Project (NSHAP), a representative probability sample of home-dwelling, older U.S. adults age 57 to 85 years. Exposure to NO2 pollution was assessed using measurements obtained from the U.S. Environmental Protection Agency (EPA) Aerometric Information Retrieval System (AIRS) ambient monitoring site closest to each respondent's home. We tested the association between NO2 exposure and olfactory dysfunction using multivariate logistic regression.

RESULTS

Among older adults in the United States, 22.6% had impaired olfactory function, defined as ≤3 correct (out of 5) on the odor identification test. Median NO2 exposure during the 365 days prior to the interview date was 14.7 ppb (interquartile range [IQR], 10.8 to 19.7 ppb). An IQR increase in NO2 exposure was associated with increased odds of olfactory dysfunction (OR, 1.35; 95% CI, 1.07 to 1.72), adjusting for age, gender, race/ethnicity, education, cognition, comorbidity, smoking, and season of the home interview (n = 1823).

CONCLUSION

We show for the first time that NO2 exposure is associated with olfactory dysfunction in older U.S. adults. These results suggest an important role for NO2 exposure on olfactory dysfunction, and, potentially, nasal disease more broadly.

Comorbidity and chronic conditions in the National Social Life, Health and Aging Project (NSHAP), Wave 2

OBJECTIVE

The goals of this paper were: (a) to promote research using the National Social Life, Health and Aging Project (NSHAP) Wave 2 data by providing relevant background information for a broad range of chronic conditions and (b) to provide a framework for combining these chronic conditions into informative comorbidity indices.

METHOD

The chronic conditions measured in NSHAP Wave 2 were grouped across several health domains: cardiovascular, endocrine and metabolic, cancer, lung, inflammatory and bone, neurological, and sensorimotor. Prevalences for each condition were reported as percentages and were also estimated separately by age group and gender. Additionally, 2 comorbidity indices were created: a Modified Charlson Comorbidity Index (CCI) that included conditions associated with mortality risk and the NSHAP Comorbidity Index (NCI) that included conditions from the Modified CCI as well as additional conditions related to overall health and function.

RESULTS

Hypertension, incontinence, arthritis, heart conditions, cancer, and diabetes were the most prevalent conditions. In general, prevalences of most chronic conditions increased with age. Additionally, there were several notable gender differences in chronic condition prevalence. Due to the inclusion of highly prevalent conditions, such as hypertension and incontinence, the mean comorbidity index score of the NCI was higher than that of the Modified CCI.

DISCUSSION

Wave 2 of NSHAP included a variety of measures assessing the chronic conditions that are the most prevalent in older adults. These data are a valuable resource for the study of the impact of chronic conditions on overall health and aging.

Survey field methods for expanded biospecimen and biomeasure collection in NSHAP Wave 2

OBJECTIVES

The National Social Life, Health, and Aging Project is a nationally representative, longitudinal survey of older adults. A main component is the collection of biomeasures to objectively assess physiological status relevant to psychosocial variables, aging conditions, and disease. Wave 2 added novel biomeasures, refined those collected in Wave 1, and provides a reference for the collection protocols and strategy common to the biomeasures. The effects of aging, gender, and their interaction are presented in the specific biomeasure papers included in this Special Issue.

METHOD

A transdisciplinary working group expanded the biomeasures collected to include physiological, genetic, anthropometric, functional, neuropsychological, and sensory measures, yielding 37 more than in Wave 1. All were designed for collection in respondents' homes by nonmedically trained field interviewers.

RESULTS

Both repeated and novel biomeasures were successful. Those in Wave 1 were refined to improve quality, and ensure consistency for longitudinal analysis. Four new biospecimens yielded 27 novel measures. During the interview, 19 biomeasures were recorded covering anthropometric, functional, neuropsychological, and sensory measures and actigraphy provided data on activity and sleep.

DISCUSSION

Improved field methods included in-home collection, temperature control, establishment of a central survey biomeasure laboratory, and shipping, all of which were crucial for successful collection by the field interviewers and accurate laboratory assay of the biomeasures (92.1% average co-operation rate and 97.3% average assay success rate). Developed for home interviews, these biomeasures are readily applicable to other surveys.