The Nutritional Impact of COVID‐19‐Induced Olfactory Dysfunction

Abstract

Despite well‐known associations between nutrition and chemosensory dysfunction, very little is known regarding the nutritional impact of COVID‐19‐related chemosensory dysfunction. A retrospective cohort study using the National COVID Cohort Collaborative (N3C) Database was performed to evaluate the risk of malnutrition in individuals with COVID‐19‐induced anosmia. Statistical analysis among groups was performed by odds ratio (OR) calculations (95% confidence interval [CI]). 19,384 (0.05%) COVID‐19‐positive adults without preexisting malnutrition were identified with a new diagnosis of anosmia. Within this subgroup, there were significant odds of developing overnutrition (OR 1.36, 95% CI [1.26, 1.46], P < .0001) and any malnutrition diagnosis (OR 1.34, 95% CI [1.25, 1.44], P < .0001), but not undernutrition (OR 0.88, 95% CI [0.66, 1.16], P = .35). These large database findings indicate that chemosensory losses in COVID‐19 patients may increase the risk of subsequent overnutrition on a broad, national scale.

Level of Evidence. Level 3.

Chemosensory dysfunction is a well‐recognized cardinal symptom of COVID‐19 infection. Approximately 62% of COVID‐19 patients suffer from anosmia, with 60% to 70% of individuals recovering within 4 weeks. ¹ , ² Up to 7% of individuals may continue experiencing long‐term olfactory deficits. ³ Preliminary investigations suggest multiple risk factors; however, none have been definitively identified. ⁴ , ⁵ , ⁶ , ⁷ , ⁸

In one of the few reports addressing nutritional status as a risk factor, our group recently demonstrated that overnutrition may increase the risk of COVID‐19‐induced chemosensory dysfunction, whereas undernutrition may be slightly protective. ³ While such findings shed light on nutritional status as a risk factor for the development of chemosensory dysfunction, the effects of COVID‐19‐induced chemosensory impairment on nutrition remain uncertain, lacking large‐scale population analysis. Further investigation into the nutritional impact of post‐COVID‐19‐induced chemosensory deficits is warranted, given the high prevalence and known behavioral, emotional, and consumption‐related changes that anosmic individuals may exhibit. The aim of this study is to investigate the impact of COVID‐19‐induced olfactory dysfunction on nutritional status post‐COVID diagnosis.

Methods

A retrospective cohort study using version 131 of the National COVID Cohort Collaborative (N3C) Database was performed. The Data Enclave contains data from 22.8 million patients from 84 contributing sites in the United States, including patients of a range of comorbidity status from both clinic and hospitalized settings. The database was queried from 3/1/2020 to 7/10/2025 for adults aged 18 or older with positive COVID‐19 test results, systematized nomenclature of medicine clinical term (SNOMED) code of smell and taste disturbance within 2 weeks of positive test date, and over‐ or under‐nutrition‐related diagnosis (Appendix A). COVID‐19‐positive adults without reported chemosensory deficits were similarly identified and used as a control group. Diagnosis of chemosensory disturbance included patients with either objective or subjective distortion, as no known SNOMED code discriminates between the two. Individuals with no appointments prior to COVID‐19 diagnosis or with diagnoses of both under‐ and overnutrition were excluded. Selection of nutrition‐related diagnosis was guided by the World Health Organization (WHO) definition of malnutrition. ⁹ , ¹⁰ The undernutrition cohort included micro‐ or macronutrient deficiencies, underweight individuals, and conditions encompassing wasting and stunting. The overnutrition cohort included micro‐ or macronutrient excess, obese and overweight populations, and individuals with excessive or abnormal weight gain. Two existing studies on overnutrition and undernutrition were used to compare and confirm selected diagnoses. ¹¹ , ¹² Diet‐related noncommunicable diseases were excluded as they may be considered confounding variables by independently influencing nutritional status, thereby distorting relationships observed between the variables. Statistical analysis consisted of odds ratio calculations (95% CI). This study was conducted under data use request RP‐64CD77 with level 3 data access and approved by VCU IRB HM20022747. Authorship was determined using ICMJE recommendations.

Results

Of 3,845,086 COVID‐19 patients without a pre‐existing diagnosis of malnutrition, 19,384 (0.05%) were identified with olfactory dysfunction. Among this subgroup, 67 (0.35%) individuals had a future diagnosis of undernutrition, 1431 (7.38%) individuals had a diagnosis of overnutrition, and 1533 (7.91%) individuals had a diagnosis of any malnutrition post COVID‐19 infection. Odds ratios (ORs) were calculated comparing patients with COVID‐19‐induced olfactory dysfunction and subsequent malnutrition to patients with COVID‐19 and subsequent malnutrition, but without reported chemosensory deficits. COVID‐19‐induced olfactory dysfunction was associated with greater odds of subsequent overnutrition (OR 1.36, 95% CI [1.26, 1.46], P < .0001) and any malnutrition (OR 1.34, 95% CI [1.25, 1.44], P < .0001), but was not associated with greater odds of undernutrition (OR 0.88, 95% CI [0.66, 1.16], P = .35) (Table 1).

Table 1.

Odds of Anosmic Individuals Developing Under‐, Over‐, and Any Nutritional Impact

Population	Total (n)	Under‐nutrition (n)	Over‐nutrition (n)	Any malnutrition (n)
C + A+	19,384	67	1431	1533
C + A−	3,825,702	18,971	170,526	195,731
Total	3,845,086	19,038	171,957	197,264
Odds ratio		0.88	1.36	1.34
P‐value		P = .35	P < .0001	P < .0001
95% CI		[0.66, 1.16]	[1.26, 1.46]	[1.25, 1.44]

Abbreviations: C+A+, positive for COVID‐19 and anosmia/olfactory dysfunction; C+A−, Positive for COVID‐19 and without diagnosis of anosmia/olfactory dysfunction; CI, confidence interval.

Discussion

These results suggest that individuals experiencing COVID‐19‐induced chemosensory deficits may have an increased risk of overnutrition and malnutrition. In accordance with these findings, a recent cohort study demonstrated that individuals with a year of persistent olfactory dysfunction experienced a statistically significant increase in BMI. ¹³ It is possible that these corresponding results are due to changes in dietary preferences or consumption patterns.

Anosmia has a well‐known impact on gustation, which may cause increased mealtime consumption. Ferrulli et al. provided a current review of studies analyzing post‐COVID olfactory dysfunction and changes in diet/body mass, ¹⁴ with most evidence supporting overnutrition as a consequence. However, there is a lack of research utilizing large databases containing data from outpatient and hospitalized patients—this was a key advantage of N3C in this analysis.

In a recent study assessing the subjective impact of post‐COVID‐19 chemosensory dysfunction, anosmic individuals reported increased consumption in an attempt to satisfy cravings due to diminished flavor perception. ¹⁵ Furthermore, Liu et al demonstrated that anosmia may result in compensatory emotional overeating due to diminished enjoyment of food and quality of life. ¹² , ¹⁵ Anosmia may also alter food preferences, leading to low‐quality diets. Individuals with olfactory deficits may exhibit lower intake of produce and whole grains with increased consumption of seasoning, salt, sugar, and fat. ¹⁶ , ¹⁷ , ¹⁸ These changes may be accounted for by the types of taste receptors on the tongue and positive textural mouthfeel of fat. ¹⁹ , ²⁰

Behavioral modifications may have resulted from the COVID‐19 pandemic and transitions to remote work. Literature has demonstrated increases in sedentary behavior, decreases in physical activity, and a greater incidence of overeating during this period. ²¹ , ²² However, it is unlikely that these wide‐spanning risks accounted for the results of the current study.

The present study is not without limitations. The N3C data is sourced from multiple institutions and harmonized through the Observational Medical Outcome Partnership (OMOP) common data model, possibly resulting in data loss and translation errors. Inclusion in the database also requires clinicians to code for patients' conditions. Lack of documentation may have partially led to lower observed reported rates of anosmia than expected. ¹ , ² As this is a systemic error, calculated odds ratios were unlikely to be impacted. Due to the lack of existing SNOMED codes, olfactory deficits were not quantified by severity. These results also may not apply to other countries, as the database only contains information from U.S. health systems.

Conclusions

Chemosensory losses in patients with COVID‐19 may increase the risk of overnutrition and malnutrition. Clinicians should consider counseling post‐COVID patients on the potential impact on nutritional status.

Author Contributions

Elizabeth M. Mastoloni, design, conduct, analysis, presentation; Aaron Tucker, design, conduct, analysis; Evan French, design, conduct, analysis; Daniel H. Coelho, design, conduct, analysis.

Disclaimer

The N3C Publication committee confirmed that this manuscript msid:2086.211 is in accordance with N3C data use and attribution policies; however, this content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health or the N3C program.

IRB

The N3C data transfer to NCATS is performed under a Johns Hopkins University Reliance Protocol # IRB00249128 or individual site agreements with NIH. The N3C Data Enclave is managed under the authority of the NIH; information can be found at https://ncats.nih.gov/n3c/resources.

Disclosures

Author's note: This article was presented at the Triological Society Annual Meeting at COSM 2024; May 15‐19, 2024; Chicago, Illinois.

Competing interests

None.

Funding source

None.

Supporting information

List of systematized nomenclature of medicine (SNOMED) clinical term codes for chemosensory deficit and malnutrition.

Individual Acknowledgements Legend: List of core contributors to the National COVID Cohort Collaborative (N3C) Database.