Association between diabetes mellitus and olfactory dysfunction: current perspectives and future directions

Zaghloul, Hadeel; Pallayová, Mária; AL-Nuaimi, Omair Ali; Hovis, Kenneth R.; Taheri, Shahrad

doi:10.1111/dme.13542

Cited by 38 publications

(32 citation statements)

References 76 publications

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“…Although not conducted in a systematic fashion, prior review articles have highlighted the potential utility of olfactory testing for early detection of central diabetic neuropathy and diabetes‐related cognitive impairment . In fact, OI has been implicated in Alzheimer's dementia, with support for its use as a predictive marker of cognitive decline .…”

Section: Discussionmentioning

confidence: 99%

“…The lack of stratification in some studies presents a limitation, as the pathophysiologic differences in subtype may play a role in the potential mechanism or baseline characteristics that explain the association between OI and diabetes. In T2D, hyperglycemia can result in increased cortical thinning of the orbitofrontal cortex, contributing to accelerated cognitive decline . Central manifestations of diabetic neuropathy affecting the olfactory nerve has also been proposed as a mechanism .…”

Section: Discussionmentioning

confidence: 99%

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

Kim

Windon

Lin

2019

Laryngoscope Investig Oto

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Background Evidence suggests that olfactory impairment (OI) may be a degenerative neurologic complication of diabetes; however, the association is not yet well established. The objective of this work was to systematically review existing literature on the association between diabetes and OI in adults, with meta‐analysis of evaluable studies. Methods A literature search encompassing 358 abstracts from the last 75 years in PubMed, EMBASE, and Cochrane was performed. English‐language articles investigating adults with diabetes and OI in comparison to control groups with original data and ≥7 subjects were included. The Newcastle‐Ottawa scale was applied for quality assessment. Two investigators independently reviewed all articles. For meta‐analysis, the odds ratio of OI in diabetes compared with control groups was calculated using the fixed effects model. Results The initial search yielded 358 abstracts, from which 21 articles were reviewed and 11 articles (n = 6,747) were included. Studies included were case‐control (64%) or cross‐sectional (36%) with evidence level 3b. On the Newcastle‐Ottawa scale, the mean quality assessment score for case‐control and cross‐sectional studies was 7.4 (maximum of 9) and 7.0 (maximum of 10), respectively. A statistically significant association between diabetes and olfaction compared with controls was found in 6 (55%) of the 11 articles. Four studies were eligible for meta‐analysis, which yielded an overall odds of having OI with diabetes as 1.58 times more likely than in control groups (95% CI [1.16, 2.16]; I2 = 10.3%). Conclusions The reviewed studies support a significant association between diabetes and OI. Further studies are warranted to characterize this association. Level of Evidence 3a

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

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

Kim

Windon

Lin

2019

Laryngoscope Investig Oto

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“…Importantly, the olfactory functional connectivity and olfactory behavior served as mediator factors between pancreatic function and executive function in diabetes. Cross-sectional studies using olfactory measurements or tools such as the University of Pennsylvania Smell Identification test, Open Essence test, and "Sniffin" Sticks have revealed that patients with diabetes have lower odor threshold, discrimination, and identification scores (16,(25)(26)(27)(28). Similarly, in this study, patients with type 2 diabetes had significantly reduced ability to detect odors compared with the control, though they were all within normal range of olfactory threshold and general cognitive status (Table 1).…”

Section: Discussionmentioning

confidence: 99%

Altered Odor-Induced Brain Activity as an Early Manifestation of Cognitive Decline in Patients With Type 2 Diabetes

Zhang

Wang

et al. 2018

Diabetes

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Type 2 diabetes is reported to be associated with olfactory dysfunction and cognitive decline. However, whether and how olfactory neural circuit abnormalities involve cognitive impairment in diabetes remains uncovered. This study thus aimed to investigate olfactory network alterations and the associations of odor-induced brain activity with cognitive and metabolic parameters in type 2 diabetes. Participants with normal cognition, including 51 patients with type 2 diabetes and 41 control subjects without diabetes, underwent detailed cognitive assessment, olfactory behavior tests, and odor-induced functional MRI measurements. Olfactory brain regions showing significantly different activation between the two groups were selected for functional connectivity analysis. Compared with the control subjects, patients with diabetes demonstrated significantly lower olfactory threshold score, decreased brain activation, and disrupted functional connectivity in the olfactory network. Positive associations of the disrupted functional connectivity with decreased neuropsychology test scores and reduced pancreatic function were observed in patients with diabetes. Notably, the association between pancreatic function and executive function was mediated by olfactory behavior and olfactory functional connectivity. Our results suggested the alteration of olfactory network is present before clinically measurable cognitive decrements in type 2 diabetes, bridging the gap between the central olfactory system and cognitive decline in diabetes.

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“…Lietzau et al showed that type 2 diabetes may impair olfactory memory and odor detection and decreases neurogenesis in the olfactory bulb [17]. Several hypotheses have been made to try to explain the olfactory dysfunction in diabetes, including the possibility that endocrine and vascular changes may lead to neuropathy and damage to the olfactory nerve [18,19]. Obesity and overweight are also associated with olfactory dysfunction [20].…”

Section: Introductionmentioning

confidence: 99%

Olfactory Memory in Depression: State and Trait Differences between Bipolar and Unipolar Disorders

Kazour

Richa

Char³

et al. 2020

Brain Sciences

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Background: Changes in olfactory recognition memory may constitute sensory markers in depression. Significant differences may exist between unipolar and bipolar depression. Our study compares olfactory memory between control, unipolar, and bipolar patients in depressed and euthymic states in order to identify potential markers of depression. Methods: 176 participants were recruited in 5 groups: depressed bipolar (DB), euthymic bipolar (EB), depressed unipolar (DU), euthymic unipolar (EU), and controls (HC). The participants had a standardized clinical and olfactory assessment (olfactory memory, evaluation of pleasantness, intensity, familiarity, and emotional aspect of smells). Results: DU, DB, and EU patients had a deficit in olfactory memory compared to HC. DB patients had lower capacity to recognize new odors. DB and DU patients had more limited detection of unfamiliar odors than HC. DB patients rated odors as less pleasant compared to the other groups. All groups had lower hedonic ratings than HC. DB patients had lower emotional ratings than EU patients. Conclusions: Olfactory memory is impaired in depressive states, thus constituting a state marker of depression. Impairments in olfactory memory persist after remission of bipolar depression, thus constituting a possible trait marker of bipolarity. Hedonic rating differentiates unipolar from bipolar depression. This is the first study that identifies a sensory marker differentiating between unipolar and bipolar depression.

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Association between diabetes mellitus and olfactory dysfunction: current perspectives and future directions

Cited by 38 publications

References 76 publications

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

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

Altered Odor-Induced Brain Activity as an Early Manifestation of Cognitive Decline in Patients With Type 2 Diabetes

Olfactory Memory in Depression: State and Trait Differences between Bipolar and Unipolar Disorders

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