Long-term diet and risk of Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) infection and Coronavirus Disease 2019 (COVID-19) severity

Background The role of diet on Coronavirus Disease 2019 (COVID-19) is emerging. We investigated the association between usual diet before the onset of the pandemic and risk and severity of subsequent SARS-CoV-2 infection. Methods We included 42,935 participants aged 55-99 y in 2 ongoing cohort studies, the Nurses' Health Study II and Health Professionals Follow-up Study, who completed a series of COVID-19 surveys in 2020 and 2021. Using data from FFQs before COVID-19, we assessed diet quality using the Alternative Healthy Eating Index (AHEI)-2010, the alternative Mediterranean Diet (AMED) score, an Empirical Dietary Index for Hyperinsulinemia (EDIH), and an Empirical Dietary Inflammatory Pattern (EDIP). We calculated multivariable-adjusted ORs and 95% CIs for Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) infection and severity of COVID-19 after controlling for demographic, medical, and lifestyle factors. Results Among 19,754 participants tested for SARS-CoV-2, 1941 participants reported a positive result. Of these, 1327 reported symptoms needing assistance and another 109 were hospitalized. Healthier diets, represented by higher AHEI-2010 and AMED scores and lower EDIH and EDIP scores, were associated with lower likelihood of SARS-CoV-2 infection (quartile 4 compared with quartile 1: OR: 0.80; 95% CI: 0.69, 0.92 for AHEI-2010; OR: 0.78; 95% CI: 0.67, 0.92 for AMED; OR: 1.36; 95% CI: 1.16, 1.57 for EDIH; and OR: 1.13; 95% CI: 0.99, 1.30 for EDIP; all P-trend <= 0.01). In the analysis of COVID-19 severity, participants with healthier diet had lower likelihood of severe infection and were less likely to be hospitalized owing to COVID-19. However, associations were no longer significant after controlling for BMI and pre-existing medical conditions. Conclusions Diet may be an important modifiable risk factor for SARS-CoV-2 infection, as well as for severity of COVID-19. This association is partially mediated by BMI and pre-existing medical conditions.