Cod Liver Oil for Nutritional Support

Research suggests that cod liver oil, as a source of vitamin D, may play a supporting role in immune function, with one large UK observational study finding that regular vitamin D supplement use was associated with a lower likelihood of failing to mount an antibody response after COVID-19 vaccination. However, a large Phase 3 randomized controlled trial found that vitamin D supplementation did not produce a statistically significant reduction in acute respiratory infections, including COVID-19, at a population level, even when blood levels were successfully raised. The remaining studies in this set are observational in nature and focused primarily on vaccine type, socioeconomic factors, and regional outbreak dynamics, offering limited direct evidence specific to cod liver oil or nutritional supplementation. Overall, the evidence here is mixed and indirect, and readers should be aware that none of these studies examined cod liver oil itself as an intervention, which is a meaningful limitation when drawing conclusions about its role in nutritional support.