Olfactory Dysfunction in Type 2 Diabetes Mellitus

Abstract

We evaluated olfactory dysfunction in 154 adults (74 men, mean age 60.9±11.9 years), of whom 119 had type 2 diabetes mellitus (T2DM). Olfactory function was assessed with "Sniffin' Sticks." A total Threshold-Discrimination-Identification (TDI) score was calculated. Type 2 diabetes mellitus, hypertension, and hyperlipidemia were associated with lower olfactory scores (all TDI scores<0.001). Age was negatively associated with odor threshold, odor identification, and TDI score (P=.009, <.001, and <.001, respectively). After adjusting for age, gender, body mass index, smoking, alcohol, diabetes, hypertension, hyperlipidemia, and cardiovascular disease, only T2DM and hypertension were associated with TDI score (R square=0.281). Diabetic complications were associated with olfactory dysfunction (P=.006): TDI scores were lower in the presence of diabetic peripheral neuropathy (P=.017) and retinopathy (P=.047). In conclusion, T2DM and hypertension are independently associated with olfactory dysfunction while diabetic peripheral neuropathy and retinopathy are significantly associated with lower olfactory scores. The clinical relevance of these findings needs to be further examined.

Heterogeneity of odorant identification impairment in patients with Alzheimer’s Disease

“…Hypertension and diabetes were also included as covariates to exclude the known effect of their relationship on olfactory function 33 . Olfaction also diminishes with age 34 .…”

Mechanisms Linking Olfactory Impairment and Risk of Mortality

“…This could explain, at least in part, the independent association found between type 2 diabetes mellitus (in which insulin resistance represents the key mechanism) and OI (Gopinath et al, 2012;Gouveri et al, 2014;Yulug et al, 2019). OI in type 2 diabetes mellitus might also be due to microvascular injury since OI was mainly found in diabetic patients already suffering from the microvascular complications of this disease (Gouveri et al, 2014). Regarding mortality studies, diabetes mellitus was associated with OI in one study (Gopinath et al, 2012) but was not in another one more recent (Liu et al, 2019).…”

“…Still, there remain controversies in the literature regarding the association between malnutrition and OI in geriatric patients (Gunzer, 2017). Similarly, the relationship between OI and obesity yield contradictory results, some studies demonstrating a correlation (mainly through increased threshold detection of odors (Richardson et al, 2004;Palouzier-Paulignan et al, 2012), while others did not (Gouveri et al, 2014). Some authors suggest that the wide range of both etiologies and endocrinologic consequences of obesity could explain these conflicting findings (Palouzier-Paulignan et al, 2012).…”

“…Indeed, a recent study found that older adults with high insulin resistance (quantified by the HOMA-IR test) had an approximately 2-fold increased odds of OI compared with subjects with low insulin resistance (Min and Min, 2018). This could explain, at least in part, the independent association found between type 2 diabetes mellitus (in which insulin resistance represents the key mechanism) and OI (Gopinath et al, 2012;Gouveri et al, 2014;Yulug et al, 2019). OI in type 2 diabetes mellitus might also be due to microvascular injury since OI was mainly found in diabetic patients already suffering from the microvascular complications of this disease (Gouveri et al, 2014).…”

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

“…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].…”