Adiposity measures predict olfactory processing speed in older adult carriers of the apolipoprotein E ε4 allele

Smell Impairment in Stage I-II Obesity: Correlation with Biochemical Regulators and Clinical Aspects

OBJECTIVE

To evaluate the differences in olfactory sensitivity, nutritional habits, levels of modulators of feeding and smell, bioelectrical impedance analysis (BIA) measures and metabolic assays between two groups of participants with stage I and II obesity and reciprocal relationships between these parameters.

METHODS

Eighteen participants with stage I (11 female; mean age = 54.3 ± 13.1 years) and 20 participants with stage II (10 female; mean age = 54.5 ± 11.9) obesity underwent a food frequency questionnaire and Sniffin' Sticks® test battery, anthropometric parameters, and BIA measurements as well as metabolic assays (including plasma levels of leptin, insulin, ghrelin, glucose, insulin-like growth factor-1 [IGF-1] and usual laboratory parameters).

RESULTS

The stage II obesity participants demonstrated significant higher levels of insulin and leptin and lower levels of ghrelin and IGF-1, a reduction in odor identification (OI) and in total olfactory score, and an increase in visceral and total fat percentage. Among a mosaic of multiple correlations, ghrelin was found to positively correlate with OI and leptin negatively with odor discrimination.

CONCLUSION

The present study expands the notions positing the olfactory perception - and its connections with metabolic cues, foods habits and BIA measures - changes across the two most important obesity stages. This could ameliorate clinical and research deepening of obesity-related olfactory behavior with possible consequences on diagnosis, treatment and prevention of onset and development of obesity, thus opening possible future strategies involving multidisciplinary contributions.

LEVEL OF EVIDENCE

Level 3 Laryngoscope, 2022.

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.

Differential Effects of BMI on Brain Response to Odor in Olfactory, Reward and Memory Regions: Evidence from fMRI

：Obesity has reached epidemic proportions, motivating research into the underlying mechanisms. Olfaction is a powerful mediator of food consumption, and obesity has been associated with altered olfactory sensitivity. The current study used an event-related functional magnetic resonance imaging (fMRI) to examine the central processing of odor in humans to gain insight into the effect of the body mass index (BMI) on the neural processes involved in rating the pleasantness of a food odor during a hunger state and in a satiety state. We hypothesized that, during the hedonic evaluation of food odor, BMI would be associated with differences in brain activation within olfactory and higher order processing areas important for perception, reward, and memory. We report novel findings of a dissociation between the relationship between BMI and activation in reward areas and in olfactory and odor memory areas, i.e., activation in reward areas decreased as BMI increased, whereas activation in primary olfactory and memory regions increased as BMI increased. A greater BMI is associated with decreased activation in the reward and frontal regions, supporting a blunted reward response in obesity. These findings have important potential implications for decision making, response inhibition, and reward-based behaviors that may play key roles as causal and maintenance factors in obesity. In contrast, a greater BMI is associated with an increased activation in the primary olfactory and memory areas, which was observed during a hunger state. These results raise the speculative hypothesis that high BMI may be associated with hyperactivation in the olfactory and memory areas, and that over time, the resulting excitotoxic effects may contribute to neurodegenerative changes in these areas.

Prevalence and Correlates of Olfactory Dysfunction in Old Age: A Population-Based Study

Background:

Olfactory dysfunction (OD) in old age is associated with poor health outcomes. Interrelationships among different correlates of OD can offer insights into the underlying mechanisms, but to date remain understudied.

Methods:

Odor identification performance and self-reported olfactory functioning were studied in 2,234 people aged 60–90 years, who were free of neurodegenerative disease and enrolled in the Swedish National Study on Aging and Care in Kungsholmen (SNAC-K) study, Stockholm, Sweden. OD was defined as the inability to identify more than 10 out of 16 odors (free or cued identification) in a standardized odor identification task. OD prevalence was estimated, and associations with demographic, genetic, vascular, clinical, and behavioral factors, as well as their interactions were examined using multiple logistic regression analyses.

Results:

Overall prevalence of OD was 24.8% (CI: 23.1; 26.6). Self-reports were characterized by low sensitivity (35%), but high specificity (87%). Advancing age (OR = 15.50, CI = 9.40; 26.10 between the first and last age group), and history of coronary heart disease (OR = 1.35, 95% CI = 1.04; 1.75) were the principal factors associated with an increased probability of OD, whereas female gender (OR = 0.53, 95% CI = 0.43; 0.66) and more years of education (OR = 0.97, CI 0.94; 0.99) were linked to a lower probability. Exploratory interaction analyses indicated that prevalence of OD was particularly elevated among Apolipropotein E (APOE) ε4 allele carriers who were also obese, and that being physically active counteracted the negative impact of cerebrovascular disease on OD.

Conclusion:

Demographic and genetic factors, but also prior and current health insults, are linked to OD in old age. Modulatory effects of behavioral factors highlight their value as possible prevention targets.

Gender Difference in the Epidemiological Association between Metabolic Syndrome and Olfactory Dysfunction: The Korea National Health and Nutrition Examination Survey

Metabolic syndrome (MetS) is associated with a higher risk of morbidity and/or mortality for various chronic diseases. The aim of this study was to investigate the relationships of MetS and its components with olfactory dysfunction in a representative Korean population. We analyzed the data from the Korean National Health and Nutrition Examination Survey (2008–2010). A total of 11,609 adults who underwent otolaryngological examination were evaluated. The olfactory function was classified as normosmia or hyposmia by a self-report questionnaire according to the sense problems of smell during the past 3 months. MetS was diagnosed if a participant had at least three of the following: (1) WC ≥90 cm in men and ≥80 cm in women; (2) fasting blood sugar ≥ 100 mg/dL or medication use for elevated glucose; (3) fasting triglyceride ≥ 150 mg/dL or cholesterol-lowering medication use; (4) HDL-cholesterol <40 mg/dL in men and <50 mg/dL in women or cholesterol-lowering medication use; and (5) SBP ≥ 130 mmHg and/or DBP ≥ 85 mmHg or antihypertensive drug use for patients with a history of hypertension. The prevalence of olfactory dysfunction in the study population was 6.3%. The prevalence of olfactory dysfunction was significantly higher in older people with MetS than in those without MetS in both sexes (male, 42.0 ± 3.4% vs. 34.7 ± 0.9%, p = 0.0354; female, 46.2 ± 2.8% vs. 37.8 ± 0.8%, p = 0.0026). However, elevated waist circumference, elevated fasting glucose, elevated triglycerides, reduced HDL cholesterol, elevated blood pressure, severe stress, depressed mood, and suicidal ideation were significantly associated with olfactory dysfunction only in women. After controlling for confounders, olfactory dysfunction was significantly associated with MetS (odds ratio, 1.352; 95% confidence interval, 1.005–1.820) only in women. MetS are associated with olfactory dysfunction only in Korean women.

Individuals at risk for Alzheimer's disease show differential patterns of ERP brain activation during odor identification

BACKGROUND

Studies suggest that older adults at risk of developing Alzheimer's disease may show olfactory processing deficits before other signs of dementia appear.

METHODS

We studied 60 healthy non-demented individuals, half of whom were positive for the genetic risk factor the Apolipoprotein E ε4 allele, in three different age groups. Event-related potentials to visual and olfactory identification tasks were recorded and analyzed for latency and amplitude differences, and plotted via topographical maps.

RESULTS

Varying patterns of brain activation were observed over the post-stimulus epoch for ε4- versus ε4+ individuals on topographical maps. Individuals with the ε4 allele demonstrated different ERP peak latencies during identification of olfactory but not visual stimuli. High correct ApoE classification rates were obtained utilizing the olfactory ERP.

CONCLUSIONS

Olfactory ERPs demonstrate functional decline in individuals at risk for Alzheimer's disease at much earlier ages than previously observed, suggesting the potential for pre-clinical detection of AD at very early stages.