The history of vitamin D is closely intertwined with the investigation of deficiency diseases such as rickets and osteomalacia. As early as the 17th century, physicians reported skeletal deformities in both children and adults, although the exact causes of these ailments remained unknown. Medical texts described symptoms such as bowed limbs and enlarged joints - typical features of what we now recognize as vitamin D deficiency. Engravings from works like De Rachitide by Francis Glisson (1650) (see figure 1) depict children with visibly deformed bodies. Still, the root cause of these abnormalities remained elusive for centuries.

Rickets became increasingly common in Europe during the Industrial Revolution. Widespread air pollution from coal fires, overcrowded housing, and limited exposure to sunlight in rapidly growing cities all contributed to the disease’s prevalence. Urban children, in particular, received little sunlight, impairing the body’s natural synthesis of vitamin D. The disease, marked by soft and deformed bones, soon became known as the “English disease.” One of the most well-known fictional cases is Charles Dickens’ character Tiny Tim in A Christmas Carol, who embodies the image of a child afflicted by rickets in Victorian London.

By the late 19th and early 20th centuries, scientific inquiry began to unravel the environmental and dietary factors contributing to the disease. The Polish physician Sniadecki had already observed that rural children, exposed to more sunlight, suffered from rickets far less frequently than their urban peers - an early clue pointing to the role of sunlight. British doctor Sir Edward Mellanby, meanwhile, emphasized the importance of diet, noting that cod liver oil, rich in fat-soluble compounds, had a healing effect on rickets.

This launched a scientific debate: Was light or nutrition the key factor? Research by Theobald Palm and others revealed that the disease was more common in northern climates, while children in sunnier regions were largely unaffected. In the 1910s and 1920s, experiments by scientists such as Kurt Huldschinsky and Alfred Hess (see figure 2) confirmed that ultraviolet (UV) light exposure could cure rickets. Around the same time, feeding studies showed that certain fats -especially cod liver oil - supported bone development and prevented the disease.

These discoveries were part of a broader shift in medical thinking. In 1912, Polish biochemist Casimir Funk (see figure 3) coined the term "vitamines" (vital amines), proposing that tiny amounts of specific dietary compounds were essential for human health. This concept laid the foundation for the modern understanding of vitamins. American researchers Elmer McCollum and Marguerite Davis identified fat-soluble factors - later known as vitamins A and D - that were vital for growth and health. Edward Mellanby demonstrated that puppies fed a vitamin D-deficient diet developed rickets, which could be reversed by administering cod liver oil.

The realization that vitamin D could also be synthesized in the skin through exposure to UV light bridged the two competing theories - dietary intake and sunlight. In the 1920s, scientist Harry Steenbock (see figure 2) at the University of Wisconsin showed that irradiated foods could prevent rickets. Steenbock demonstrated that irradiating yeast or other foods produced an active substance, later identified as vitamin D2. This discovery led to the development of vitamin D-enriched foods, particularly milk, which became a cornerstone of public health efforts to combat rickets in children.

To manage the patent for this process, Steenbock and his colleagues founded the Wisconsin Alumni Research Foundation (WARF), one of the first university-based technology transfer organizations. WARF funded numerous scientific endeavors, including research by future Nobel Prize laureates. The fortification of food with vitamin D became a globally adopted strategy, significantly reducing the incidence of rickets.

But while these achievements marked tremendous progress, the scientific story of vitamin D was far from complete. The journey from identifying a mysterious childhood disease to isolating a specific nutrient illustrates the collaborative power of observation, experimentation, and innovation. What began as an attempt to understand skeletal deformities in children ultimately led to the discovery of one of the most important vitamins in human biology. 

Sources:

DeLuca, H. F. (2014). History of the discovery of vitamin D and its active metabolites. BoneKEy Reports, 3, 479 Source

Holick, M. F. (2023). The One-Hundred-Year Anniversary of the Discovery of the Sunshine Vitamin D3: Historical, Personal Experience and Evidence-Based Perspectives. Nutrients, 15(3), 593. Source

Jones, G. (2022). 100 YEARS OF VITAMIN D: Historical aspects of vitamin D. Endocrine Connections, 11(4), e210594. Source

Piro, A., Tagarelli, G., Lagonia, P., Tagarelli, A., & Quattrone, A. (2010). Casimir Funk: His Discovery of the Vitamins and Their Deficiency Disorders. Annals of nutrition & metabolism, 57, 85–88. Source