- In this prospective, smartphone-based study, 592,571 adults in the U.S. and U.K. completed a short food frequency questionnaire and tracked their COVID-19 symptoms and test results from March to December 2020
- The risk of developing COVID-19 was 9% lower for participants in the highest category of the healthful Plant-Based Diet Index (indicating highest consumption of healthy plant-based foods), than those in the lowest category
- The beneficial influence of a healthy diet was most pronounced for severe COVID-19 (41% lower risk)
- Compared with individuals who had the lowest community-level socioeconomic deprivation and highest diet quality, those living in areas with the highest socioeconomic deprivation who had the lowest diet quality were at 47% greater risk of COVID-19
- 30% of COVID-19 cases would have been prevented if one of the two exposures (poor diet or deprivation) were not present
Almost immediately after the COVID-19 pandemic began in the U.S. and U.K., investigators in the two countries began partnering on the COVID-19 Symptom Study, a smartphone-based investigation of risk factors. They recently determined diet quality is independently associated with the risk of COVID-19 and its severity.
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Jordi Merino, PhD, a research associate in the Diabetes Unit of the Endocrine Division at Massachusetts General Hospital, Andrew T. Chan, MD, MPH, chief of the Clinical and Translational Epidemiology Unit in the Department of Medicine and vice chair of Clinical Research in the Division of Gastroenterology, and colleagues published the findings in Gut.
The investigators used general and social media to recruit healthy participants starting on March 24, 2020. Each day the participants received a smartphone prompt to report any COVID-19 symptoms, health care visits and testing results. They were followed until December 2, 2020.
This analysis included 592,571 nonpregnant adult participants who completed a short food frequency questionnaire (27 foods) to assess their usual pre-pandemic diet (February 2020). Diet data were used to compute a score on the healthful Plant-Based Diet Index (hPDI), which emphasizes intake of healthy plant foods, such as fruits, vegetables, legumes and whole grains, and has been associated with lower risk of type 2 diabetes, fatty liver disease and coronary artery disease.
The primary outcome was COVID-19 risk defined using a validated algorithm that Dr. Chan and colleagues previously described in Nature Medicine. It predicts whether a participant has been infected with SARS-CoV-2 on the basis of their reported symptoms, age and sex.
In a multivariable-adjusted model, COVID-19 risk was 9% lower for participants in the highest (best) category of the hPDI compared with those in the lowest category.
Multivariable models were adjusted for age, sex, race/ethnicity, community-level socioeconomic deprivation, health care worker status, comorbidities, BMI, smoking status and physical activity.
The findings were consistent when the researchers additionally adjusted for regional differences in community transmission and participant reports about mask-wearing.
Compared with individuals who had the lowest community-level socioeconomic deprivation and highest diet quality, those living in areas with the highest socioeconomic deprivation who had the lowest diet quality were at 47% greater risk of COVID-19.
These models estimate that 30% of COVID-19 cases would have been prevented if one of the two exposures (poor diet or deprivation) had not been present.
In secondary analyses, COVID-19 risk was defined as a self-report of a positive test. The highest category of diet quality, as compared with the lowest, was associated with:
- 18% lower risk of COVID-19
- 41% lower risk of severe COVID-19 (hospitalization and any type of breathing support)
Implications for Public Health
The joint association of diet quality and socioeconomic deprivation was higher than the sum of the risk associated with each factor alone. This suggests diet quality directly influences susceptibility to COVID-19 and its progression beyond the impact of socioeconomic deprivation.
Public health interventions to improve nutrition and poor metabolic health, as well as address social determinants of health, may be important for reducing the burden of the pandemic.
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