The Scientific Quest: How Was Vitamin D Deficiency Discovered?

November 23, 2025 •

3 min read

Rickets, a debilitating bone disease now known to be caused by vitamin D deficiency, once plagued up to 80% of children in the smog-filled, industrial cities of 17th-century Britain. This devastating epidemic spurred centuries of scientific inquiry into its mysterious origins, ultimately leading to the discovery of vitamin D and its critical role in human health.

Quick Summary

This article details the historical path to understanding vitamin D deficiency, focusing on key figures, animal experiments, and the dual discoveries connecting dietary intake and sun exposure to bone health.

Key Points

The 'English Disease': Rickets was once an epidemic, particularly in sun-starved industrial cities, leading to centuries of confusion about its cause.
Mellanby's Contribution: Sir Edward Mellanby used controlled animal experiments with dogs to prove that cod liver oil contained a fat-soluble, anti-rachitic factor.
McCollum's Definitive Proof: Elmer McCollum's groundbreaking 1922 experiment showed that the anti-rachitic factor was a new vitamin, which he named vitamin D, distinct from vitamin A.
Sunlight's Cure: Kurt Huldschinsky and Harry Steenbock independently demonstrated that UV light could cure rickets by activating a precursor in the skin and food.
Public Health Success: The dual discoveries of a dietary source and UV activation of vitamin D led to food fortification and supplementation programs that effectively eradicated rickets in many developed nations.
Modern Relevance: While the historical context is rooted in rickets, the discovery of vitamin D deficiency continues to inform modern understanding of its broader health implications.

The 'English Disease' and Early Observations

Before the 20th century, the bone-deforming disease known as rickets was a profound mystery. First described in the 17th century, it was called "the English Disease" due to its prevalence in Great Britain. Physicians like Daniel Whistler and Francis Glisson documented the characteristic skeletal deformities. The industrial revolution worsened the problem as city smog reduced sun exposure. Early theories about the cause varied, but in 1890, Theobald Palm hypothesized that lack of sunlight was linked to the disease after observing lower rates in sunny climates.

The Dietary Factor: Edward Mellanby's Dog Experiments

In the early 1900s, Sir Edward Mellanby investigated the dietary causes of rickets using dogs. He found that a diet high in oatmeal and lack of sunlight caused rickets, which could then be cured with cod liver oil. Mellanby initially believed the anti-rachitic factor was vitamin A, concluding that rickets was a deficiency disease.

The Naming of Vitamin D by Elmer McCollum

American biochemist Elmer McCollum further investigated Mellanby's findings. By 1922, McCollum had already identified vitamins A and B. He conducted experiments showing that cod liver oil still cured rickets even after its vitamin A content was destroyed through oxidation. This proved a distinct, previously unknown fat-soluble nutrient was responsible, which he named vitamin D.

The Dual Cures: Sunlight and Irradiated Foods

Simultaneously, Kurt Huldschinsky in 1919 discovered that ultraviolet (UV) light from a mercury-vapor lamp could cure rickets in children. This supported Palm's earlier theory about sunlight. The puzzle of two cures—cod liver oil and UV light—was solved by researchers like Harry Steenbock. He showed that UV light could increase the vitamin D content of foods by activating a precursor, demonstrating the body could synthesize the vitamin. Steenbock patented this process, leading to food fortification and the decline of rickets in developed countries.

Comparing the Discovery Paths of Vitamin D


Aspect	Dietary Discovery Path	Sunlight/UV Discovery Path
Key Researchers	Edward Mellanby, Elmer McCollum	Theobald Palm, Kurt Huldschinsky, Harry Steenbock
Initial Observation	Cod liver oil cured rickets in experimental dogs.	Rickets was less common in sunny regions.
Pivotal Experiment	McCollum destroys vitamin A in oil; it still cures rickets, proving a new vitamin exists.	Huldschinsky cures rachitic children with artificial UV light.
Resulting Innovation	Identification of vitamin D as the anti-rachitic factor.	Discovery that UV radiation converts a precursor into vitamin D.
Public Health Application	Supplementation programs and food fortification (e.g., milk).	Increased awareness of the importance of sun exposure.

The Enduring Legacy of the Discovery

The discovery of vitamin D was a landmark public health achievement. The combined efforts of researchers like Mellanby, McCollum, Huldschinsky, and Steenbock transformed rickets from a widespread epidemic into a preventable condition through initiatives like milk fortification. This history highlights the value of scientific inquiry. For more on the chemical history, see "History of the discovery of vitamin D and its active metabolites".

Conclusion

The discovery of vitamin D deficiency resulted from a multi-faceted scientific effort, not a single event. It involved early clinical observations, Mellanby's animal experiments highlighting a dietary factor, and McCollum's definitive identification and naming of vitamin D. The crucial finding that sunlight also played a role led to effective public health strategies like food fortification, ultimately making rickets largely preventable and treatable.

Frequently Asked Questions

The condition, known as rickets, was first clearly described in the mid-17th century by English physicians Daniel Whistler (1645) and Francis Glisson (1650).

Sir Edward Mellanby used animal experiments to prove that cod liver oil could cure and prevent rickets, demonstrating that the disease was caused by a dietary deficiency.

In 1922, McCollum deliberately destroyed the vitamin A content in cod liver oil but found that it still cured rickets, proving that a different, previously unknown nutrient was responsible. He named it vitamin D.

In 1919, Kurt Huldschinsky demonstrated that UV light could cure rickets, revealing that the body could produce the anti-rachitic factor endogenously and was not solely reliant on diet.

Following Harry Steenbock's patented process of irradiating foods with UV light to increase their vitamin D content, public health campaigns in the 1920s led to the fortification of milk and other products, dramatically reducing rickets cases.

While no longer a widespread epidemic in developed nations due to food fortification, vitamin D deficiency can still occur in certain at-risk populations and is linked to numerous health conditions beyond bone health.

The name "rickets" likely derives from an Old English word related to twisting, referring to the characteristic skeletal deformities of the condition.