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

Abstract

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

Epidemiological, otolaryngological, olfactory and gustatory outcomes according to the severity of COVID-19: a study of 2579 patients

“…In our study, diabetes was associated with the development of GD and there was a trend of association with Sniffin'Stick test results. The association between diabetes and the development of OD is well known and supported by a recent meta-analysis [20]. Similar findings were observed in patients with GD, confirming the potential role of diabetes in the development of sense disorders [21].…”

Altered olfaction, obesity, and glycosylated hemoglobin; Indicators of accelerated ageing in apparently healthy, Pakistan's young aged population

“…The Mona Lisa Study highlighted that obesity and increased blood glucose is directly linked with poor cognitive impairment and is already evident in middle-aged individuals 28 . Studies have suggested that olfaction disorders are basically due to neuro-degeneration and could occur as a diabetic complication 29 . Since impaired olfaction is an indicator of ageing in the elderly, but it was observed in the early ages in the current study due the presence of diabetes and obesity in the study participants.…”

Development of the Spanish Version of Sniffin’s Sticks Olfactory Identification Test: Normative Data and Validity of Parallel Measures

“…The tests for evaluating the ability to identify odors have important cultural components [ 10 , 39 , 74 , 79 , 80 , 81 , 82 ]. The odorants of a well-validated identification test should be familiar to individuals from each country.…”

“…Olfactory tests are necessary tools for adequate assessment of olfactory function [ 1 ]. The use of olfactory assessment tests has become more relevant in recent years, due to clinical and research findings that indicate the existence of olfactory alterations derived from traumatic injuries as brain injury [ 2 , 3 ], in surgical or medical procedures for the treatment of some diseases such as larynx tumors requiring partial or total laryngectomy [ 4 ], treatment with radiotherapy [ 5 ], or pathologies with alterations of the sense of smell such as arterial hypertension [ 6 ], liver disease [ 7 , 8 ], diabetes mellitus [ 9 , 10 ], rhinitis, sinusitis [ 11 , 12 ], autoimmune diseases [ 13 , 14 ], inflammatory diseases [ 15 ], anxiety [ 16 , 17 ], major depression [ 18 , 19 , 20 , 21 ], schizophrenia [ 22 ], autism [ 23 ], and neurodegenerative diseases [ 24 , 25 ], such as frontotemporal dementia [ 26 , 27 , 28 ], amyotrophic lateral sclerosis [ 29 ], Parkinson’s disease [ 30 , 31 , 32 , 33 ], or Alzheimer’s disease [ 33 , 34 , 35 , 36 ].…”