By Brant Cebulla, Vitamin D Council

What is vitamin D? The query hasn’t always prompted as straight forward a response as one might expect. Researchers often squabble over whether to classify vitamin D as a vitamin, hormone, pro-hormone, pre-hormone, essential nutrient and more. So why do we call it vitamin D?

In the nineteenth century, German chemists believed that an adequate diet solely consisted of proteins, carbohydrates, fats and minerals, unaware of nutrients we now call vitamins.

Scientists began questioning this: They noticed certain diseases like scurvy and beriberi could be prevented by certain foods. However, when these foods were purified they somehow lost their ability to treat the diseases. A biochemist names Casimir Funk coined the term “vital animes,” theorizing that there were vital compounds called animes in food, essential to the diet of animals. This term paved the way for the current descriptive word, “vitamins.”

Around 1926, Professor Elmer McCullum of the University of Wisconsin-Madison discovered that some type of fat-soluble substance in butter prevented xerophthalmia (dry eyes). He later called this factor “vitamin A.”

In later animal experiments, he used this butter and compared it to cod liver oil. He noticed that animals that took cod liver oil developed neuritis, while the animals taking the butter did not. This was attributable to a set of vitamins they penned “vitamin B,” which was not found in cod liver oil.

Physicians elsewhere discovered a nutrient in food that staved off scurvy in guinea pig experiments. They called this factor “vitamin C.”

Professor McCollum transferred to John Hopkinds, continuing his experiments on fat-soluble nutrients. Cod liver oil was long known to prevent and cure rickets, and they thought that vitamin A might also be responsible for curing rickets. McCollum wanted to know for sure.

In another series of experiments, McCollum aerated and heated cod liver oil to destroy the vitamin A content. Although the altered cod liver oil no longer prevented xerophthalmia, it still retained its ability to cure rickets. Thus, he reasononed there must be another nutrient in cod liver oil that prevents and cures rickets, so he named it “vitamin D.”

Around the same time, a different group of researchers independently found that sunlight or artificial UV light could prevent and cure rickets, too. While some scientists observed this connection as far back as a hundred years earlier, these experiments were the first to verify that sunlight indeed plays a role in rickets.

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