This paper offers the first case study of the marketing of codliver oil in Sweden (1920–1930), following the discovery of vitamins A and D. Drawing upon a large dataset of cod liveroil advertisements from the Swedish Newspaper Archive, it uses multimodal critical discourse analysis to investigate how language and other semiotic resources (e.g. image, typography, color) work together to convey the benefits of cod liver oil intake. It identifies three overarching themes—scientific rationality, scientific motherhood, and nature—noting how advertisements were aimed squarely at mothers and struck a balancebetween vitamins as scientifically formulated products and mythical, natural substances to convince them that cod liveroil was necessary for their children. Exploring how cod liver oil was marketed from a historical perspective shows how nutritional research gained prominence and became of increasing importance for marketing, as well as how food, through science, became incorporated into a consumerist lifestyle. It also provides a way to deconstruct contemporary marketing practices, thereby enabling consumers to rethink products framed as indispensable for their health.