Associations of Hearing Loss and Dual Sensory Loss With Mortality: A Systematic Review, Meta-analysis, and Meta-regression of 26 Observational Studies With 1 213 756 Participants

Hearing Loss and Reduced Income Growth: A Longitudinal Socioeconomic Analysis

OBJECTIVE

Hearing loss (HL) has been linked to negative socioeconomic states, including low income. This study examines the relationship between HL and income growth.

STUDY DESIGN

Longitudinal observational study.

SETTING

Multicentered US epidemiologic study (Hispanic Community Health Study, HCHS).

METHODS

Using data from 2 waves of the HCHS, we analyzed the association between HL and income growth in adults ages 18 to 74 years using generalized estimating equations. The exposure was HL, measured by 4-frequency pure-tone average (PTA). The outcome was yearly household income growth, with income graded on a 10-bracket scale from <$10,000 to >$100,000. Models controlled for demographics, hearing aid use, and vascular risk.

RESULTS

A total of 1342 participants met inclusion criteria. At visit 1, average age was 47.6 years (SD = 12.2), and average PTA was 13.9 decibels (dB, SD = 9.5). Average follow-up was 5.9 years (SD = 0.6). There was a significant time × HL interaction: with each 10 dB worsening in HL, the odds of belonging to a higher versus a lower income bracket changed by a factor of 0.979 (P < .001) between waves 1 and 2. In other words, the odds of belonging to a higher income group decreased with worsening HL. At 38.6 dB, the odds for income growth became <1, indicating income loss rather than growth.

CONCLUSION

Increased HL is associated with reduced income growth, including the possibility of negative growth (ie, income decline). This study emphasizes the value of including socioeconomic measures in randomized controlled trials assessing the impact of HL treatment and the importance of extended follow-up for study participants.

The association between disability and all-cause mortality in low-income and middle-income countries: a systematic review and meta-analysis

BACKGROUND

There are 1·3 billion people with disabilities globally. On average, they have poorer health than their non-disabled peers, but the extent of increased risk of premature mortality is unknown. We aimed to systematically review the association between disability and mortality in low-income and middle-income countries (LMICs).

METHODS

We searched MEDLINE, Global Health, PsycINFO, and EMBASE from Jan 1, 1990 to Nov 14, 2022. Longitudinal epidemiological studies in any language with a comparator group that measured the association between disability and all-cause mortality in people of any age were eligible for inclusion. Two reviewers independently assessed study eligibility, extracted data, and assessed risk of bias. We used a random-effects meta-analysis to calculate the pooled hazard ratio (HR) for all-cause mortality by disability status. We then conducted meta-analyses separately for different impairment and age groups.

FINDINGS

We identified 6146 unique articles, of which 70 studies (81 cohorts) were included in the systematic review, from 22 countries. There was variability in the methods used to assess and report disability and mortality. The meta-analysis included 54 studies, representing 62 cohorts (comprising 270 571 people with disabilities). Pooled HRs for all-cause mortality were 2·02 (95% CI 1·77-2·30) for people with disabilities versus those without disabilities, with high heterogeneity between studies (τ2=0·23, I2=98%). This association varied by impairment type: from 1·36 (1·17-1·57) for visual impairment to 3·95 (1·60-9·74) for multiple impairments. The association was highest for children younger than 18 years (4·46, [3·01-6·59]) and lower in people aged 15-49 years (2·45 [1·21-4·97]) and people older than 60 years (1·97 [1·65-2·36]).

INTERPRETATION

People with disabilities had a two-fold higher mortality rate than people without disabilities in LMICs. Interventions are needed to improve the health of people with disabilities and reduce their higher mortality rate.

FUNDING

UK National Institute for Health and Care Research; and UK Foreign, Commonwealth and Development Office.

The association between disability and mortality: a mixed-methods study

BACKGROUND

Globally, 1·3 billion people have a disability and are more likely to experience poor health than the general population. However, little is known about the mortality or life expectancy gaps experienced by people with disabilities. We aimed to undertake a systematic review and meta-analysis of the association between disability and mortality, compare these findings to the evidence on the association of impairment types and mortality, and model the estimated life expectancy gap experienced by people with disabilities.

METHODS

We did a mixed-methods study, which included a systematic review and meta-analysis, umbrella review, and life expectancy modelling. For the systematic review and meta-analysis, we searched MEDLINE, Global Health, PsycINFO, and Embase for studies published in English between Jan 1, 2007, and June 7, 2023, investigating the association of mortality and disability. We included prospective and retrospective cohort studies and randomised controlled trials with a baseline assessment of disability and a longitudinal assessment of all-cause mortality or cause-specific mortality. Two reviewers independently assessed study eligibility, extracted the data, and assessed risk of bias. We did a random-effects meta-analysis to calculate a pooled estimate of the mortality rate ratio for people with disabilities compared with those without disabilities. We did an umbrella review of meta-analyses examining the association between different impairment types and mortality. We used life table modelling to translate the mortality rate ratio into an estimate of the life expectancy gap between people with disabilities and the general population. The systematic review and meta-analysis is registered with PROSPERO, CRD42023433374.

FINDINGS

Our search identified 3731 articles, of which 42 studies were included in the systematic review. The meta-analysis included 31 studies. Pooled estimates showed that all-cause mortality was 2·24 times (95% CI 1·84-2·72) higher in people with disabilities than among people without disabilities, although heterogeneity between the studies was high (τ2=0·28, I2=100%). Modelling indicated a median gap in life expectancy of 13·8 years (95% CI 13·1-14·5) by disability status. Cause-specific mortality was also higher for people with disabilities, including for cancer, COVID-19, cardiovascular disease, and suicide. The umbrella review identified nine meta-analyses, which showed consistently elevated mortality rates among people with different impairment types.

INTERPRETATION

Mortality inequities experienced by people with disabilities necessitate health system changes and efforts to address inclusion and the social determinants of health.

FUNDING

National Institute for Health and Care Research, Rhodes Scholarship, Indonesia Endowment Funds for Education, Foreign, Commonwealth and Development Office (Programme for Evidence to Inform Disability Action), and the Arts and Humanities Research Council.

Socioeconomic and ethnic disparities associated with access to cochlear implantation for severe-to-profound hearing loss: A multicentre observational study of UK adults

BACKGROUND

Patients with severe-to-profound hearing loss may benefit from management with cochlear implants. These patients need a referral to a cochlear implant team for further assessment and possible surgery. The referral pathway may result in varied access to hearing healthcare. This study aimed to explore referral patterns and whether there were any socioeconomic or ethnic associations with the likelihood of referral. The primary outcome was to determine factors influencing referral for implant assessment. The secondary outcome was to identify factors impacting whether healthcare professionals had discussed the option of referral.

METHODS AND FINDINGS

A multicentre multidisciplinary observational study was conducted in secondary care Otolaryngology and Audiology units in Great Britain. Adults fulfilling NICE (2019) audiometric criteria for implant assessment were identified over a 6-month period between 1 July and 31 December 2021. Patient- and site-specific characteristics were extracted. Multivariable binary logistic regression was employed to compare a range of factors influencing the likelihood of implant discussion and referral including patient-specific (demographics, past medical history, and degree of hearing loss) and site-specific factors (cochlear implant champion and whether the hospital performed implants). Hospitals across all 4 devolved nations of the UK were invited to participate, with data submitted from 36 urban hospitals across England, Scotland, and Wales. Nine hospitals (25%) conducted cochlear implant assessments. The majority of patients lived in England (n = 5,587, 86.2%); the rest lived in Wales (n = 419, 6.5%) and Scotland (n = 233, 3.6%). The mean patient age was 72 ± 19 years (mean ± standard deviation); 54% were male, and 75·3% of participants were white, 6·3% were Asian, 1·5% were black, 0·05% were mixed, and 4·6% were self-defined as a different ethnicity. Of 6,482 submitted patients meeting pure tone audiometric thresholds for cochlear implantation, 311 already had a cochlear implant. Of the remaining 6,171, 35.7% were informed they were eligible for an implant, but only 9.7% were referred for assessment. When adjusted for site- and patient-specific factors, stand-out findings included that adults were less likely to be referred if they lived in more deprived area decile within Indices of Multiple Deprivation (4th (odds ratio (OR): 2·19; 95% confidence interval (CI): [1·31, 3·66]; p = 0·002), 5th (2·02; [1·21, 3·38]; p = 0·05), 6th (2·32; [1·41, 3·83]; p = 0.05), and 8th (2·07; [1·25, 3·42]; p = 0·004)), lived in London (0·40; [0·29, 0·57]; p < 0·001), were male (females 1·52; [1·27, 1·81]; p < 0·001), or were older (0·97; [0·96, 0·97]; p < 0·001). They were less likely to be informed of their potential eligibility if they lived in more deprived areas (4th (1·99; [1·49, 2·66]; p < 0·001), 5th (1·75; [1·31, 2·33], p < 0·001), 6th (1·85; [1·39, 2·45]; p < 0·001), 7th (1·66; [1·25, 2·21]; p < 0·001), and 8th (1·74; [1·31, 2·31]; p < 0·001) deciles), the North of England or London (North 0·74; [0·62, 0·89]; p = 0·001; London 0·44; [0·35, 0·56]; p < 0·001), were of Asian or black ethnic backgrounds compared to white patients (Asian 0·58; [0·43, 0·79]; p < 0·001; black 0·56; [0·34, 0·92]; p = 0·021), were male (females 1·46; [1·31, 1·62]; p < 0·001), or were older (0·98; [0·98, 0·98]; p < 0·001). The study methodology was limited by its observational nature, reliance on accurate documentation of the referring service, and potential underrepresentation of certain demographic groups.

CONCLUSIONS

The majority of adults meeting pure tone audiometric threshold criteria for cochlear implantation are currently not appropriately referred for assessment. There is scope to target underrepresented patient groups to improve referral rates. Future research should engage stakeholders to explore the reasons behind the disparities. Implementing straightforward measures, such as educational initiatives and automated pop-up tools for immediate identification, can help streamline the referral process.

Association Between Hearing Loss and Cardiovascular Disease: A Meta-analysis

OBJECTIVE

Hearing loss (HL) has been postulated to be linked to cardiovascular diseases (CVDs) via vascular mechanisms, but epidemiological associations remain unclear. The study aims to clarify the association between HL and stroke, coronary artery disease (CAD), and any CVD.

DATA SOURCES

PubMed, Embase, and SCOPUS from inception until April 27, 2022.

REVIEW METHODS

Three blinded reviewers selected observational studies reporting stroke, CAD, and any CVD in patients with HL, compared to individuals without HL. We extracted data, evaluated study bias using the Newcastle-Ottawa scale, following Preferred Reporting Items for Systematic Reviews and Meta-analyses guidelines and a PROSPERO-registered protocol (CRD42022348648). We used random-effects inverse variance meta-analyses to pool the odds ratios (ORs) for the association of HL with stroke, CAD, and any CVD.

RESULTS

We included 4 cohort studies (N = 940,771) and 6 cross-sectional studies (N = 680,349). Stroke, CAD, and any CVD were all strongly associated with HL. The overall pooled OR of the association between HL and stroke was 1.26 (95% confidence interval [CI] = 1.16-1.37, I2  = 78%), and was 1.33 (95% CI = 1.12-1.58) and 1.29 (95% CI = 1.14-1.45) for low- and high-frequency HL, respectively. Minimal publication bias was observed, with minimal change to pooled effect size following trim and fill. Similarly, the pooled OR of the association between HL and CAD was 1.36 (95% CI = 1.13-1.64, I2  = 96%), while that between HL and any CVD was 1.38 (95% CI = 1.07-1.77, I2  = 99%).

CONCLUSION

Our findings suggest that HL and CVD are closely related. Physicians treating patients with HL should be cognizant of this association and view HL in the broader context of general health and aging.

Cataract Surgery and Cognitive Benefits in the Older Person: A Systematic Review and Meta-analysis

TOPIC

This systematic review and meta-analysis aims to clarify the association of cataract surgery with cognitive impairment and dementia.

CLINICAL RELEVANCE

The association between vision impairment and cognitive decline is well-established. However, the cognitive benefits of cataract surgery are less clear. Given the lack of cure for dementia, identifying modifiable risk factors is key in caring for patients with cognitive deficits.

METHODS

The study was conducted following Preferred Reporting Items for Systematic Review and Meta-analyses guidelines. PubMed, Embase, and Cochrane Library were searched from inception through October 11, 2022, for studies reporting the effect of cataract surgery on cognitive impairment and dementia. We pooled maximally adjusted hazard ratios (HRs) for dichotomous outcomes and ratio of means (RoM) for continuous outcomes using a random-effects model. Heterogeneity was examined using sensitivity and subgroup analyses. The quality of evidence was evaluated using the Newcastle-Ottawa scale, Cochrane risk-of-bias tool for randomized trials, and Grading of Recommendations, Assessment, Development and Evaluations (GRADE) guidelines.

RESULTS

This review included 24 articles comprising 558 276 participants, of which 19 articles were analyzed qualitatively. The bias of studies ranged from low to moderate, and GRADE extended from very low to low. Cataract surgery was associated with a 25% reduced risk of long-term cognitive decline compared with those with uncorrected cataracts (HR, 0.75; 95% confidence interval [CI], 0.72-0.78). This cognitive benefit was seen across various cognitive outcomes and remained robust to sensitivity analyses. Participants who underwent cataract surgery showed a similar risk of long-term cognitive decline as healthy controls without cataracts (HR, 0.84; 95% CI, 0.66-1.06). Additionally, cataract surgery was associated with a 4% improvement in short-term cognitive test scores among participants with normal cognition (RoM, 0.96; 95% CI, 0.94-0.99), but no significant association was observed among participants with preexisting cognitive impairment.

DISCUSSION

Cataract surgery may be associated with a lower risk of cognitive impairment and dementia, and cataract-associated vision impairment may be a modifiable risk factor for cognitive decline. Physicians should be aware of the cognitive sequelae of cataracts and the possible benefits of surgery. The cognitive benefits of cataract surgery should be investigated further in randomized trials.

FINANCIAL DISCLOSURE(S)

The author(s) have no proprietary or commercial interest in any materials discussed in this article.

Association between hearing aid use and mortality in adults with hearing loss in the USA: a mortality follow-up study of a cross-sectional cohort

BACKGROUND

Hearing loss has been identified as an independent risk factor for negative health outcomes and mortality. However, whether rehabilitation with hearing aid use is associated with lower mortality is currently unknown. This study aimed to examine the associations of hearing loss, hearing aid use, and mortality in the USA.

METHODS

In this cross-sectional, follow-up study, we assessed 9885 adults (age 20 years and older) who participated in the National Health and Nutrition Examination Survey between 1999 and 2012 and completed audiometry and hearing aid use questionnaires (1863 adults with hearing loss). Main measures included hearing loss (speech-frequency pure-tone average) and hearing aid use (never users, non-regular users, and regular users). Mortality status of the cohort was linked to the National Death Index up to Dec 31, 2019. Cox proportional regression models were used to examine the association between hearing loss, hearing aid use, and mortality while adjusting for demographics and medical history.

FINDINGS

The cohort consisted of 9885 participants, of which 5037 (51·0%) were female and 4848 (49·0%) were male with a mean age of 48·6 years (SD 18·1) at baseline. The weighted prevalence of audiometry-measured hearing loss was 14·7% (95% CI 13·3-16·3%) and the all-cause mortality rate was 13·2% (12·1-14·4) at a median 10·4 years of follow-up (range 0·1-20·8). The rate of regular hearing aid use among adults with hearing loss was 12·7% (95% CI 10·6-15·1). Hearing loss was an independent risk factor associated with higher mortality (adjusted hazard ratio [HR] 1·40 [95% CI 1·21-1·62]). Among individuals with hearing loss, the adjusted mortality risk was lower among regular hearing aid users in comparison with never users (adjusted HR 0·76 [0·60-0·95]) accounting for demographics, hearing levels, and medical history. There was no difference in adjusted mortality between non-regular hearing aid users and never users (adjusted HR 0·93 [0·70-1·24]).

INTERPRETATION

Regular hearing aid use was associated with lower risks of mortality than in never users in US adults with hearing loss when accounting for age, hearing loss, and other potential confounders. Future research is needed to investigate the potential protective role of hearing aid use against mortality for adults with hearing loss.

FUNDING

None.

Residential proximity to major roadways and hearing impairment in Chinese older adults: a population-based study

BACKGROUND

With rapid urban sprawl, growing people are living in the vicinity of major roadways. However, little is known about the relationship between residential proximity to major roadways and hearing impairment (HI).

METHODS

We derived data from the 2018 wave of the Chinese Longitudinal Healthy Longevity Survey, and included 13,775 participants aged 65 years or older. Multivariate logistic regressions were employed to examine the association between residential proximity to major roadways and HI. The effects of corresponding potentially modifiable factors were studied by three-way interaction analyses. Sensitivity analyses were performed to verify the robustness of the results.

RESULTS

The prevalence of HI was 38.3%. Participants living near major roadways were more likely to have a higher socioeconomic status. An exposure-response relation between residential proximity to major roadways and HI was observed (Ptrend < 0.05). Compared with individuals living > 300 m away from major roadways, the adjusted odds ratios (OR) were 1.07 (95% CI: 0.96-1.24), 1.15 (95% CI: 1.07-1.34), and 1.12 (95% CI: 1.01-1.31) for those living 101-200 m, 50-100 m, and < 50 m away from the roadways, respectively. Particularly, the association was more pronounced among individuals exposed to carbon monoxide (CO) pollution or opening windows frequently (Pinteraction < 0.05). Three-way interaction analyses confirmed that participants exposed to CO pollution and frequently leaving windows open had the highest OR of 1.73 (95% CI: 1.58-1.89).

CONCLUSIONS

This nation-wide cohort study suggested that residential proximity to major roadways was significantly associated with an increased exposure-response risk of HI in Chinese older adults. Exposure to CO pollution and opening windows frequently might strengthen the relations.

Associations between hearing loss and clinical outcomes: population-based cohort study

Background

Hearing loss (HL) is a leading cause of disability worldwide, but its clinical consequences and population burden have been incompletely studied.

Methods

We did a retrospective population-based cohort study of 4,724,646 adults residing in Alberta between April 1, 2004 and March 31, 2019, of whom 152,766 (3.2%) had HL identified using administrative health data. We used administrative data to identify comorbidity and clinical outcomes, including death, myocardial infarction, stroke/transient ischemic attack, depression, dementia, placement in long-term care (LTC), hospitalization, emergency visits, pressure ulcers, adverse drug events and falls. We used Weibull survival models (binary outcomes) and negative binomial models (rate outcomes) to compare the likelihood of outcomes in those with vs without HL. We calculated population-attributable fractions to estimate the number of binary outcomes associated with HL.

Findings

The age-sex-standardized prevalence of all 31 comorbidities at baseline was higher among participants with HL than those without. Over median follow-up of 14.4 y and after adjustment for potential confounders at baseline, participants with HL had higher rates of days in hospital (rate ratio 1.65, 95% CI 1.39, 1.97), falls (RR 1.72, 95% CI 1.59, 1.86), adverse drug events (RR 1.40, 95% CI 1.35, 1.45), and emergency visits (RR 1.21, 95% CI 1.14, 1.28) compared to those without, and higher adjusted hazards of death, myocardial infarction, stroke/transient ischemic attack, depression, heart failure, dementia, pressure ulcers and LTC placement. The estimated number of people with HL who required new LTC placement annually in Canada was 15,631, of which 1023 were attributable to HL. Corresponding estimates for new dementia among people with HL were 14,959 and 4350, and for stroke/TIA the estimates were 11,582 and 2242.

Interpretation

HL is common, is often accompanied by substantial comorbidity, and is associated with significant increases in risk for a broad range of adverse clinical outcomes, some of which are potentially preventable. This high population health burden suggests that increased and coordinated investment is needed to improve the care of people with HL.

Funding

Canadian Institutes of Health Research; David Freeze chair in health services research.

Hearing loss increases all-cause and cardiovascular mortality in middle-aged and older Chinese adults: the Dongfeng-Tongji Cohort Study

We aimed to investigate the association between hearing loss and all-cause and cardiovascular disease (CVD) mortality, and whether the relationship could be modified by chronic conditions in middle-aged and older Chinese adults. We selected 18,625 participants who underwent audiometry in 2013 from the Dongfeng-Tongji Cohort conducted in China, and followed them until December 2018. Hearing loss was grouped as normal, mild, and moderate or severe by pure-tone hearing threshold at speech (0.5, 1, and 2 kHz) and high frequency (4 and 8 kHz). We applied Cox regression models to estimate hazard ratios (HRs) and 95% confidence intervals (CIs) for all-cause and CVD mortality. Among the 18,625 participants, the mean age was 64.6 (range: 36.7-93.0) years, and 56.2% were women. A total of 1185 died, with 420 CVD deaths during a mean follow-up period of 5.5 years. The adjusted HR for all-cause and CVD mortality increased gradually with the increasing hearing threshold (All p for trend < 0.05). Compared to participants with normal hearing at speech frequency, the adjusted HRs (95% CIs) of moderate or severe hearing loss were 1.42 (1.21-1.67), 1.44 (1.10-1.89), and 1.92 (1.21-3.04) for all-cause, CVD, and stroke mortality, respectively. While moderate or severe hearing loss at high frequency was only related to an increased risk of all-cause mortality (HR, 1.60; 95% CI, 1.18-2.17). The associations were generally consistent across subgroups (All p for interaction > 0.05). Additionally, individuals with a combination of moderate or severe hearing loss and occupational noise exposure, diabetes, or hypertension had higher risk of all-cause or CVD mortality, ranging from 1.45 to 2.78. In conclusion, hearing loss was independently associated with an increased risk of all-cause and CVD mortality, in a dose-response manner. Meanwhile, hearing loss and diabetes or hypertension could jointly increase the risk of all-cause and CVD mortality.

Adverse health consequences of undiagnosed hearing loss at middle age: A prospective cohort study with the UK Biobank

OBJECTIVES

Hearing impairment is common in the middle-aged population but remains largely undiagnosed and untreated. The knowledge about to what extent and how hearing impairment matters for health is currently lacking. Thus, we aimed to comprehensively examine the adverse health consequences as well as the comorbidity patterns of undiagnosed hearing loss.

STUDY DESIGN

Based on the prospective cohort of the UK Biobank, we included 14,620 individuals (median age 61 years) with audiometry-determined (i.e., speech-in-noise test) objective hearing loss and 38,479 individuals with subjective hearing loss (i.e., tested negative but with self-reported hearing problems; median age 58 years) at recruitment (2006-2010), together with 29,240 and 38,479 matched unexposed individuals respectively.

MAIN OUTCOME MEASURES

Cox regression was used to determine the associations of both hearing-loss exposures with the risk of 499 medical conditions and 14 cause-specific deaths, adjusting for ethnicity, annual household income, smoking and alcohol intake, exposure to working noise, and BMI. Comorbidity patterns following both exposures were visualized by comorbidity modules (i.e., sets of connected diseases) identified in the comorbidity network analyses.

RESULTS

During a median follow-up of 9 years, 28 medical conditions and mortality related to nervous system disease showed significant associations with prior objective hearing loss. Subsequently, the comorbidity network identified four comorbidity modules (i.e., neurodegenerative, respiratory, psychiatric, and cardiometabolic diseases), with the most pronounced association noted for the module related to neurodegenerative diseases (meta-hazard ratio [HR] = 2.00, 95%confidence interval [CI] 1.67-2.39). For subjective hearing loss, we found 57 associated medical conditions, which were partitioned into four modules (i.e., diseases related to the digestive, psychiatric, inflammatory, and cardiometabolic systems), with meta-HRs varying from 1.17 to 1.25.

CONCLUSIONS

Undiagnosed hearing loss captured by screening could identify individuals with at greater risk of multiple adverse health consequences, highlighting the importance of screening for speech-in-noise hearing impairment in the middle-aged population, for potential early diagnosis and intervention.

Association of Olfactory Impairment With All-Cause Mortality: A Systematic Review and Meta-analysis

Importance

Olfactory impairment is highly prevalent and associated with multiple comorbidities, including neurodegenerative, cardiovascular, nutritional, and immune disorders. However, epidemiologic associations between olfactory impairment and mortality are discordant.

Objective

To systematically clarify the epidemiologic associations between olfactory impairment and mortality.

Data Sources

The PubMed, Embase, and Cochrane Library databases were searched from inception to August 13, 2021.

Study Selection

Two blinded reviewers selected observational studies published as full-length, English-language articles in peer-reviewed journals that reported the presence or severity of chronic olfactory impairment, whether objectively measured or self-reported, in association with any mortality estimate, among adults aged 18 years or older.

Data Extraction and Synthesis

Two reviewers independently extracted data, evaluated study bias using the Newcastle-Ottawa Scale, and appraised the quality of the evidence using the Grading of Recommendations Assessment, Development and Evaluation framework, following Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA) and Meta-analysis of Observational Studies in Epidemiology (MOOSE) guidelines and a PROSPERO-registered protocol. Maximally adjusted estimates were pooled using mixed-effects models, heterogeneity was measured using I2 statistics, sources of heterogeneity were investigated using meta-regression and subgroup meta-analyses, and publication bias was qualitatively and quantitatively assessed.

Main Outcomes and Measures

Hazard ratios for all-cause mortality.

Results

One retrospective cohort study and 10 prospective cohort studies (with a total of 21 601 participants) from 1088 nonduplicated records were included. Ten studies had a low risk of bias, whereas 1 study had a moderate risk; exclusion of the latter did not alter conclusions. Nine studies were included in the meta-analysis. Olfactory loss was associated with a significantly higher pooled hazard of all-cause mortality (hazard ratio, 1.52; 95% CI, 1.28-1.80; I2 = 82%). Meta-regression sufficiently explained heterogeneity, with longer mean follow-up duration weakening the pooled association, accounting for 91.3% of heterogeneity. Self-reported and objective effect sizes were similar. Associations were robust to trim-and-fill adjustment and the Egger test for publication bias. The overall quality of evidence was moderate.

Conclusions and Relevance

The findings of this systematic review and meta-analysis suggest that olfactory impairment is associated with all-cause mortality and may be a marker of general health and biological aging. Further research is required to establish the underlying mechanisms and the scope for interventions.