Discovery of Vitamin D
There's no single person who "discovered" Vitamin D. It came from several scientists working over about a decade. Here's the real timeline.
The Problem That Started It: Rickets
In the early 1900s, rickets (a bone-softening disease in children) was a massive public health problem in industrial cities in Europe and the US.
Doctors knew cod liver oil helped prevent it, but nobody knew why.
Key Players
Edward Mellanby (1918–1922) – British physiologist
Ran experiments on dogs kept indoors with no sunlight.
Found that a fat-soluble substance in food (present in cod liver oil) prevented rickets.
At the time, he wrongly believed this was Vitamin A, or that Vitamin A was somehow linked to the anti-rickets effect.
Elmer McCollum (1922) – American biochemist
This is the person usually credited with the actual identification of Vitamin D as a distinct substance.
He took cod liver oil and destroyed the Vitamin A in it (by bubbling oxygen through it), but the anti-rickets effect remained.
This proved a separate compound was responsible — not Vitamin A. He named it "Vitamin D" (the fourth vitamin identified, following A, B, C).
Harry Steenbock (1924) – American biochemist
Discovered that irradiating food with UV light increased its Vitamin D content.
This connected Vitamin D to sunlight exposure, and led to the practice of fortifying milk with Vitamin D — which is still done today.
He patented the process, which made him wealthy and funded research at the University of Wisconsin for decades.
Adolf Windaus (1920s) – German chemist
Worked out the actual chemical structure of Vitamin D and its relation to cholesterol/sterols.
Won the Nobel Prize in Chemistry in 1928 for his work on sterols and their connection to vitamins — this is the closest thing to a formal "discovery" prize tied to Vitamin D.
The Sunlight Connection
Separately, doctors had already noticed for decades that sunlight exposure treated rickets (this was known even before the vitamin was chemically identified).
It was later understood that the skin produces Vitamin D when exposed to UVB rays. This is why Vitamin D is sometimes called "the sunshine vitamin," and why it's technically not just a vitamin — it functions more like a hormone.
Bottom Line
If you need one name for a quiz or quick answer: Elmer McCollum is most commonly credited with identifying Vitamin D as a distinct nutrient in 1922.
If you're asking for accuracy over simplicity: it's a shared discovery — Mellanby found the effect, McCollum isolated and named the vitamin, Steenbock linked it to UV light and made fortification possible, and Windaus worked out its chemistry (earning the Nobel Prize for it).
One thing worth flagging: many sources oversimplify and just say "Elmer McCollum discovered Vitamin D" or "Edward Mellanby discovered Vitamin D," depending on which textbook you're reading. Neither is wrong exactly, but neither is complete either. If this is for an exam or paper, check which name your source or curriculum expects — the "correct" answer sometimes depends on the specific textbook, not the actual history.
