The Pre-Vitamin Era: Naming the Anti-Rachitic Factor
For centuries, the cause of rickets, the "English disease" that caused bone deformities in children, remained a mystery. Observational evidence connected lack of sunlight and poor diet to the condition, with cod liver oil being a recognized, if poorly understood, treatment. Early scientific investigations were less focused on naming the substance and more on isolating and understanding the anti-rachitic effect. The journey toward a name began with identifying the precursor molecules found in different sources.
The Discovery of Distinct Anti-Rachitic Compounds
The story of vitamin D's name involves two key discoveries in the early 20th century. First, German researcher Kurt Huldschinsky demonstrated in 1919 that exposing children to ultraviolet light could cure rickets, proving that a substance could be produced in the skin. Meanwhile, American scientist Elmer McCollum was experimenting with cod liver oil. He found that even after destroying its vitamin A content with oxygen, the oil retained its ability to prevent rickets. This led him to conclude in 1922 that a new, distinct fat-soluble nutrient, the fourth to be identified, was responsible. Following the existing alphabetical naming system, he called it "vitamin D."
Shortly after, researchers began isolating and characterizing the different forms of this new vitamin. In the late 1920s and early 1930s, two primary forms were identified and named based on their origin:
- Vitamin D2 (Ergocalciferol): This form was derived from irradiating ergosterol, a sterol found in plant matter and fungi. In the 1930s, preparations of irradiated ergosterol were also sometimes called "viosterol".
- Vitamin D3 (Cholecalciferol): This is the form produced in animal skin upon exposure to sunlight and found in foods like fatty fish.
Precursors and the Term "Calciferol"
Before these specific chemical names were established, the precursors themselves held importance. Ergosterol was the precursor to vitamin D2. So, for a time, irradiated ergosterol acted as the substance known to cure rickets when derived from plant sources. Later, when the distinct D2 and D3 forms were chemically characterized, the umbrella term "calciferol" was introduced. This generic name, referring to the entire group of vitamin D compounds, is another way the vitamin was known. This is why you may find sources that refer to the old name as ergosterol (the precursor to D2) or calciferol (the broader chemical name).
The Shift from "Old Names" to a Standard Terminology
The gradual adoption of the specific chemical names (ergocalciferol and cholecalciferol) and the general term "calciferol" occurred as the vitamin's biochemistry became clearer. The early, less specific names fell out of common use as scientific understanding advanced, allowing for more precise medical and nutritional terminology. This reflects a common pattern in science, where a functional name precedes a more specific chemical one as knowledge evolves.
The Legacy of Rickets and Vitamin D Fortification
After its discovery, the fortification of milk and other foods with vitamin D became a major public health success story, dramatically reducing the incidence of rickets. The old knowledge that sunlight and cod liver oil prevented the disease was finally explained by the presence of this anti-rachitic factor, and a public health campaign leveraging this knowledge cemented its importance. The history of vitamin D is a story of moving from observed phenomena to isolated substance and, eventually, to a deep understanding of its metabolic pathways.
History of Vitamin D Naming: A Comparison
| Aspect | Before 1922 | After 1922 | Today's Terminology |
|---|---|---|---|
| The Substance | Unnamed anti-rachitic factor in cod liver oil and sunlight. | Named Vitamin D by Elmer McCollum. | Still Vitamin D, a group of compounds, or Calciferol. |
| Plant Source Precursor | Ergosterol (a sterol in fungi and plants) was identified and irradiated. | Vitamin D2 (Ergocalciferol) created from irradiated ergosterol. | Vitamin D2 (ergocalciferol) remains the name for this form. |
| Animal Source Precursor | 7-dehydrocholesterol (a cholesterol precursor in skin). | Vitamin D3 (Cholecalciferol) created from UV exposure of 7-dehydrocholesterol. | Vitamin D3 (cholecalciferol) remains the name for this form. |
| Broader Chemical Term | N/A | Adopted the generic term Calciferol to refer to the group. | Calciferol is used as a generic term for vitamin D compounds. |
Conclusion
To answer the question, "what is the old name for vitamin D?", there isn't a single, simple answer. Before the official classification of "vitamin D," the anti-rachitic factor was a nameless property of cod liver oil and sunlight. Early names for precursors, such as ergosterol, and later the generic chemical term calciferol, are the closest approximations. Ultimately, the naming reflects a scientific progression from understanding a dietary cure for a disease to precisely identifying the specific compounds responsible. The enduring nickname, the "sunshine vitamin," captures the initial insight that led to its discovery, while the official term ensures medical accuracy.
One authoritative source detailing the history of vitamin D research can be found on the National Institutes of Health (NIH) website.
Frequently Asked Questions
Q: Why was the name 'vitamin D1' not used? A: The term "vitamin D1" was used for what was later discovered to be an impure mixture of vitamin D2 and other compounds, so the name was discarded.
Q: Is calciferol still used as a name today? A: Yes, calciferol is still used today as a generic chemical name for the vitamin D group, encompassing both D2 and D3 forms.
Q: What was rickets called before the discovery of vitamin D? A: Rickets, a disease of poor bone mineralization, was known by that name long before vitamin D was discovered. It was sometimes also referred to as the "English disease" due to its high prevalence in industrial Europe.
Q: What is the precursor to vitamin D3? A: The precursor to vitamin D3 is 7-dehydrocholesterol, which is found in animal skin and is converted to vitamin D3 by sunlight.
Q: What was the significance of Elmer McCollum's work? A: By proving that the anti-rachitic factor in cod liver oil was not vitamin A, McCollum isolated and named vitamin D, paving the way for targeted research and public health initiatives.
Q: What is the source of vitamin D2? A: Vitamin D2, or ergocalciferol, is obtained from plant sources and fungi, specifically through the UV irradiation of ergosterol.
Q: How did the discovery of vitamin D impact public health? A: The discovery led to the fortification of foods with vitamin D and widespread supplement use, which drastically reduced the incidence of rickets, particularly in developed nations.
