How was Paul Karrer awarded the Noble Prize?

Karrer’s initial research focused on complex metal compounds, but his most significant contributions have been made in the field of plant pigments, particularly yellow carotenoids. He clarified their chemical composition and demonstrated how some of these materials are converted into vitamin A in the body. His work assisted in establishing the ideal constitutional ratio for beta-carotene, the primary precursor to vitamin A. Before, the composition of a vitamin or provitamin was unknown. George Wald briefly worked in Karrer’s lab, studying the effects of vitamin A on the retina. The structure of ascorbic acid was later confirmed by Karrer as he deepened his investigation into vitamins B2 and E. Lactoflavin was recognized as a result of his significant contributions to the chemistry of flavins. He and Norman Haworth won the Nobel Prize for Chemistry in 1937.