In biological terms the processes that aid digestion, create vitamins and manufacture plant poisons affecting the heart might seem like being worlds apart, but in terms of their chemistry they show a remarkable degree of similarity. Establishing the chemical connections that lie at the heart of these biological processes can be said to be the hallmark of Adolf Windaus’ research career.

The key link in all these processes is a series of chemicals found widely in animals, plants and vegetables called sterols, of which the best known is cholesterol. Correctly believing that all sterols are derived from a parent substance, Windaus isolated digestive chemicals formed in the liver called bile acids, and showed that they are closely related to the sterols by successfully transforming cholesterol into one of these bile acids, cholanic acid. Windaus found the same to be true for several of the cardiotoxic compounds derived from the foxglove plant.

In perhaps his best-known achievement, Windaus discovered that the chemical precursor of vitamin D is also a member of the sterol group, and he showed how sunlight breaks one of the chemical bonds in the parent molecule, converting it into the active vitamin. The finding had major implications outside of chemistry; it revealed why exposure to sunlight can prevent rickets, a disease caused by vitamin D deficiency in humans.

By revealing a growing list of the cast of characters that make-up the sterol group, experiments by Windaus that were originally designed to uncover the structures of organic chemicals helped to develop our knowledge of physiology and medicine. Through painting a better picture of the processes occurring in healthy and diseased organisms, and by revealing the connections between different processes, Windaus also helped to strengthen the connections between different scientific disciplines.