Preliminary evidence from literature and an ongoing study in the investigators' lab suggests that cod liver oil may prevent Covid-19 and complications of Covid-19. In the present study, the investigators will examine whether this is actually the case by randomizing volunteers to take cod liver oil or placebo (corn oil) during the winter months of 2020-2021. The investigators also aim to explore whether cod liver oil can prevent other respiratory tract infections, as well as explore and confirm already known health effects and possible new health effects, in particular rare adverse events associated with cod liver oil use.~Cod liver oil is a traditional source of vitamin A, D, and E and omega-3 fatty acids and the dose administered in the study will contain 250 ug vitamin A, 10 ug vitamin D, 10 mg vitamin E, and 1,2 g omega-3 fatty acids.
A randomized, parallel-group treatment, quadruple masked, two-arm study to assess the effectiveness of cod liver oil compared to placebo in the prevention of Covid-19 and airway infections in healthy adults.~In this study, the investigators will investigate whether daily cod liver oil can prevent Covid-19 infections and reduce the severity of such infections. The investigators will also examine whether cod liver oil prevents other airway infections in healthy adults.