Sleep length/quality should have been taken into account.

Have scientists rediscovered the importance of sleep?

> Moreover, recent epidemiology suggests that melatonin usage may reduce the risk for contracting COVID-19. A recent retrospective study, examining data from 26 799 subjects in a COVID-19 registry and using propensity score matching to account for a range of covariates, found that current supplementation with melatonin was associated with a significant 28% reduction in risk for serologically detectible COVID-19 infection. Among Black Americans, this reduction in risk was a remarkable 52% (OR=0.48, 95% CI 0.31 to 0.75).

> More generally, it might be feasible to define a simple nutraceutical regimen that could reduce the risk for COVID-19 and a range of other viral infections. There is growing evidence, both case–control and ecologic, that replete vitamin D status not only markedly improves the clinical course of COVID-19, but also is associated with decreased risk for clinically detectible infection.

> COVID-19 epidemiology also suggests that higher zinc status is associated with both a better clinical course in this disorder and lower risk for infection.42 43 Especially in the elderly, who are more prone to poor zinc status, zinc supplementation has been found to boost acquired, antigen-specific immunity, while also exerting an anti-inflammatory action; such supplementation of the elderly was associated with a marked decrease in total infections in a 12-month randomised controlled trial.

> Hence, it is not unreasonable to suggest that a supplementation programme incorporating vitamin D, zinc, melatonin and possibly additional nutraceuticals could reduce risk for and aid control of COVID-19 and a range of other viral infections.