Steenbock Discovers Sunlight Increases Vitamin D in Food

With his discovery that the ultraviolet component of sunlight increases vitamin D in food, Harry Steenbock stimulated extensive research on vitamins.

Summary of Event

The discovery that exposure to sunlight increases the amount of vitamin D in food arose from two separate areas of research involving biochemistry and medicine. The first part of the investigation involved sterol, specifically cholesterol. In 1901, the importance of this substance was not yet known, and a number of able chemists had attempted to unravel the components of the substance without success. Cholesterol is one of a large group of related compounds called sterols that are found in animal and vegetable cells. In Germany, Adolf Windaus began by comparing this group of substances and found that they have a common feature in a tetracyclic carbon skeleton. He was convinced that other natural products would share in this basic skeleton. By 1919, he had demonstrated that cholesterol could be transformed into cholanic acid. By 1932, the work of Heinrich Wieland and Windaus had paid off, and the correct structure of the sterol ring was discovered. Nutrition;vitamins
Vitamins;vitamin D
[kw]Steenbock Discovers Sunlight Increases Vitamin D in Food (1924)
[kw]Sunlight Increases Vitamin D in Food, Steenbock Discovers (1924)
[kw]Vitamin D in Food, Steenbock Discovers Sunlight Increases (1924)
[kw]D in Food, Steenbock Discovers Sunlight Increases Vitamin (1924)
[kw]Food, Steenbock Discovers Sunlight Increases Vitamin D in (1924)
Vitamins;vitamin D
[g]United States;1924: Steenbock Discovers Sunlight Increases Vitamin D in Food[05950]
[c]Science and technology;1924: Steenbock Discovers Sunlight Increases Vitamin D in Food[05950]
[c]Biology;1924: Steenbock Discovers Sunlight Increases Vitamin D in Food[05950]
Steenbock, Harry
Windaus, Adolf
Eijkman, Christiaan
Hopkins, Frederick
McCollum, Elmer Verner

The story of vitamins began in 1906, when Christiaan Eijkman was seeking a cure for the tropical disease beriberi. Beriberi He observed that chickens fed on polished rice exhibited symptoms similar to the disease in humans. When the chickens were fed rice with the hulls intact, however, the disease disappeared. Consequently, Eijkman demonstrated that the disease is caused by a dietary deficiency, which was later found to be a substance called thiamine, Thiamine or vitamin B. Vitamins;vitamin B In the same year, Sir Frederick Hopkins proposed that several substances are essential for the maintenance of health and, with his colleague, Casimir Funk, named these substances “vitamins.”

In 1907, Elmer Verner McCollum was on the faculty of the University of Wisconsin, where Harry Steenbock was an undergraduate student. McCollum, who was involved in dietary and nutritional research, learned of Eijkman’s work and became convinced that a small quantity of a substance called vitamin is as essential to life as all the nutritional value of food. In 1913, he discovered a substance similar to vitamin B, except that it was found in fats; this turned out to be vitamin A. Nine years later, he contributed to the identification of vitamin D.

By the 1920’s, vitamin research was being pursued in a number of laboratories in England, Germany, and the United States. One area of research involved the disease rickets, Rickets which scientists knew could be prevented through the ingestion of fish liver oil. By the early 1920’s, it was discovered that the active agent in the fish liver oil was vitamin D. Although vitamin D could effect a cure for rickets, exposure to sunlight also proved to be effective. Scientists thus began to examine whether there were several paths toward a cure or these paths were all part of a single therapeutic process.

Steenbock brought together the two strands of medical and biochemical research in his work, in which he concentrated on the chemical analysis of livestock nutrition. He had participated in an experiment in which components of a plant were mixed in such a way that they were chemically identical but produced different nutritional results. The influence of McCollum’s experimental methods, which included the use of white mice, and Steenbock’s livestock experiment led to the beginning of the inclusion of live animal subjects in nutritional studies. Steenbock continued his research activities in nutrition through the field of vitamin studies. In 1920, he isolated a compound called carotene, which is associated with yellow foods and contains vitamin A. By 1924, Alfred F. Hess Hess, Alfred F. and Steenbock had independently exposed certain foods to sunlight and found that these foods were also effective in the cure of rickets. Somehow, light converted chemicals in the food into vitamin D. The precise mechanism for this conversion was not resolved for some time.

In 1925, Hess invited Windaus to take part in the work on vitamin D. Windaus began a collaborative effort on the study of vitamin D and continued his work on the photochemical nature of sterol. Over the years, he identified a number of other compounds with similar characteristics. Windaus believed that cholesterol was the source of vitamin D, as cholesterol exhibits similar properties when exposed to ultraviolet light. Working in Germany, Robert Pohl Pohl, Robert had identified an impurity in cholesterol, called ergosterol, Ergosterol that Hess and Windaus later proved could convert to vitamin D. Thus, by 1927, the major features of both the chemistry and the structure of sterol and vitamin D had become clear.

Through further research, Windaus found several variations of vitamin D and eventually isolated one form that was identical to the one purified from tuna fish liver oil; this was confirmed by Hans Brockman Brockman, Hans in Windaus’s laboratory. After Windaus received the 1928 Nobel Prize in Chemistry for this work, the April, 1929, issue of the Scientific Monthly published an article that analyzed why the work on rickets conducted by several noteworthy American and English scientists had been overlooked. Nobel Prize recipients;Adolf Windaus[Windaus] The article expressed the opinion that Hess and Steenbock should have been given greater credit for discovering the effects of exposure to ultraviolet light on vitamin D in food and living animals.


Long before the discovery of vitamins, scientists had observed the effects of restricted diets on both human and animal populations. Diseases that had resulted from dietary deficiencies had been described in detail. For example, the lack of fresh fruits and vegetables during long sea voyages produced scurvy, Scurvy a disease caused by the absence of vitamin C. Although it was well known that scurvy could be remedied through the ingestion of fruits and vegetables, little was known about why this was so.

Steenbock’s discovery of the effects of ultraviolet light on the production of vitamin D coincided with an extensive period of research on vitamins. The culmination of Eijkman’s initial identification of vitamin B came in 1926 with the further refinement of the vitamin. The work of B. C. P. Jansen Jansen, B. C. P. and W. F. Donath Donath, W. F. resulted in the isolation of a component called vitamin B
(thiamine). These researchers began with more than 300 kilograms (about 661 pounds) of rice polishings (husks removed from rice grains) and produced less than 100 milligrams (about 0.004 ounce) of thiamine crystal. Another resolution of an existing vitamin problem involved Steenbock’s initial observation of a relationship between vitamin D and carotene, which was later solved by Thomas Moore Moore, Thomas and Hans von Euler-Chelpin. Euler-Chelpin, Hans von In 1928, the final piece in the vitamin alphabet was provided by Albert Szent-Györgyi, Szent-Györgyi, Albert who isolated vitamin C from oranges and cabbage.

The next stage in vitamin research was the discovery of the functions of these substances. It had been demonstrated already that vitamins could cure diseases and function as growth factors. Research suggested that vitamins act on enzyme systems to regulate the respiration of cells and metabolism. In a series of experiments involving pigeons and thiamine, it was demonstrated that pigeons lacking this vitamin suffered from spasms. Thiamine is essential in the process of glucose metabolism, and without this vitamin, the mechanism for the breakdown of glucose is impaired. It became clear that thiamine directly influences five metabolic reactions that, in turn, regulate the energy flow necessary for the maintenance of the cells. These experiments thus showed the relationship between vitamin B and beriberi.

Subsequent explorations on more than twenty vitamins provided a complex picture of the roles of these substances as regulators of various mechanisms at the cellular level. Vitamins, in very small amounts, are indispensable components of food and organic life. Nutrition;vitamins
Vitamins;vitamin D

Further Reading

  • Bailey, Herbert. The Vitamin Pioneers. Emmaus, Pa.: Rodale Books, 1968. Discusses the history of the development of medical and biochemical knowledge about vitamins. The sections on vitamins B and D are comprehensive and suitable for the general reader.
  • Carpenter, Kenneth J. “A Short History of Nutritional Science: Part 3 (1912-1944).” Journal of Nutrition 133 (October, 2003): 3023-3032. Third part of a four-part series includes discussion of the research on vitamin D, placing this work in the context of the history of nutritional science in general.
  • Feldman, David, J. Wesley Pike, and Francis H. Glorieux, eds. Vitamin D. 2d ed. 2 vols. New York: Academic Press, 2004. Comprehensive reference set geared toward professionals working in endocrinology, osteology, cancer research, and related fields. First chapter provides a historical overview. Includes illustrations and index.
  • Ihde, Aaron J. The Development of Modern Chemistry. 1964. Reprint. Mineola, N.Y.: Dover, 1984. Comprehensive history of the different areas of chemistry. Chapter 24 covers the developments in biochemistry that led directly to Steenbock’s research. Topics discussed include nutrition, the search for vitamins, and metabolism.
  • Leicester, Henry M. Development of Biochemical Concepts from Ancient to Modern Times. Cambridge, Mass.: Harvard University Press, 1974. Provides a valuable overview of biochemical concepts. Chapters 15, 16, and 17 cover enzymes and cell constituents, energy production and biological oxidation, and intermediary metabolism.

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Hopkins Postulates the Presence of Vitamins

McCollum Names Vitamin D and Pioneers Its Use Against Rickets

Szent-Györgyi Discovers Vitamin C