Loss of smell associated with all cause mortality: JAMA

Singapore: The findings of a new study published in the Journal of American Medical Association suggest that olfactory impairment is linked to all-cause mortality and might be a sign of overall health and biological aging.

Olfactory impairment is common and is linked to a variety of comorbidities, including neurodegenerative, cardiovascular, nutritional, and immunological problems. However, epidemiologic links between olfactory impairment and death are contradictory. As a result, Natalie Yan-Lin Pang and colleagues undertook this investigation to rigorously elucidate the epidemiologic correlations between olfactory impairment and mortality.

The databases PubMed, Embase, and the Cochrane Library were searched from their establishment until August 13, 2021. Two blinded reviewers chose observational studies published as full-length English-language articles in peer-reviewed journals that revealed the presence or intensity of chronic olfactory deficits, whether observed directly or self-reported, in association with any mortality assessment in adults aged 18 years or older. Mixed-effects models were used to pool maximally adjusted values, I2 statistics were used to evaluate heterogeneity, meta-regression and subgroup meta-analyses were used to examine causes of heterogeneity, and publication bias was assessed subjectively and quantitatively.

The key findings of this study were as follows:

1. One retrospective cohort research and ten prospective cohort studies were considered, with a total of 1088 non duplicated data.

2. Ten studies had a low risk of bias, while one had a substantial risk; excluding the latter did not change the findings.

3. The meta-analysis includes nine studies.

4. Olfactory loss was linked to a considerably increased pooled hazard of death from any cause.

5. Meta-regression explained 91.3% of the heterogeneity, with greater mean follow-up time diminishing the pooled link.

6. The sizes of the self-reported and objective effect sizes were comparable.

7. Trim-and-fill correction and the Egger test for publication bias had no effect on the associations.

8. The overall evidence quality was mediocre.

In conclusion, this study points toward the complications associated with olfactory impairment in terms of all-cause mortality and overall health, more study is needed to determine the underlying processes and the potential for therapies.

Reference:

Pang, N. Y.-L., Song, H. J. J. M. D., Tan, B. K. J., Tan, J. X., Chen, A. S. R., See, A., Xu, S., Charn, T. C., & Teo, N. W. Y. (2022). Association of Olfactory Impairment With All-Cause Mortality. In JAMA Otolaryngology–Head & Neck Surgery. American Medical Association (AMA). https://doi.org/10.1001/jamaoto.2022.0263