Sources:
How to boost immunity with food to protect against coronavirus, flu and other viruses
Vitamin A supplementation for preventing morbidity and mortality in children from six months to five years of age
Role of Fat-Soluble Vitamins A and D in the Pathogenesis of Influenza: A New Perspective
Role of Fat-Soluble Vitamins A and D in the Pathogenesis of Influenza: A New Perspective
Vitamin A intake and plasma retinol levels in healthy elderly men and women
Significance of Vitamin A (Retinol) in Ageing
