Vitamin D1 | Ergocalciferol and Lumisterol | Complete Guide

Vitamin D1 is one of the most misunderstood names in nutrition science. Unlike vitamin D2 or D3, it is not a single molecule. Vitamin D1 is actually a 1:1 molecular compound of ergocalciferol (vitamin D2) and lumisterol, first reported in the 1920s during the earliest attempts to isolate the anti-rickets factor from irradiated ergosterol. The name has since been retired from official use, yet lumisterol itself has re-emerged in modern research as a biologically active photoproduct with photoprotective and anti-inflammatory potential. This guide explains the chemistry, history, and current science behind vitamin D1.

Related read: The complete list of vitamins — for more on how essential vitamins support daily health.

What Is Vitamin D1?

Vitamin D1 refers to a crystalline compound isolated in 1931 by Askew and colleagues from ultraviolet-irradiated ergosterol. When early chemists exposed ergosterol to UV light, they obtained a mixture of photoproducts. One of the crystalline fractions they pulled from this mixture was labeled vitamin D1.

Later analysis showed this “vitamin” was not a pure substance at all. It was a 1:1 adduct of ergocalciferol (vitamin D2) and lumisterol — two structurally related sterols locked together in a single crystal. Because true vitamins should be single active compounds, the name vitamin D1 was officially discontinued.

Researchers later renamed the pure anti-rachitic compound vitamin D2 (ergocalciferol), while the animal-derived molecule became vitamin D3 (cholecalciferol).

Why Is There No “Real” Vitamin D1 Today?

The short answer: Better isolation techniques corrected the chemistry mistake.

• Early 20th-century researchers lacked the tools to separate photoproducts cleanly.
• The compound they thought was a new vitamin was a mixture, not a pure entity.
• Once purification improved, scientists identified ergocalciferol as the true anti-rickets sterol and dropped the D1 label.
• The number “D1” was never reassigned to any other compound, which is why the vitamin D family now begins at D2.

This is why every modern textbook, including the NIH Office of Dietary Supplements Vitamin D fact sheet, lists only vitamins D2 and D3 as the two clinically relevant forms.

The Two Components of Vitamin D1

D1 is a mixture of two components, which are ergocalciferol and lumisterol, that are given below:

Attribute	Ergocalciferol (Vitamin D2)	Lumisterol
Source	UV-irradiated ergosterol from yeast, mushrooms, and fungi	Stereoisomer of ergosterol formed as a photochemical by-product during UV exposure
Historical Role	Identified as the true anti-rachitic sterol after purification from irradiated ergosterol	Originally considered biologically inactive
Modern Role / Use Today	Prescription supplements, food fortification, and vegan-friendly vitamin D products; raises circulating 25-hydroxyvitamin D levels	Recent research suggests lumisterol and its hydroxyderivatives may have photoprotective, anti-inflammatory, and anti-proliferative properties in human skin cells
Reference	NHS overview on vitamin D	PubChem CID 6436872

What Are the Symptoms of Vitamin D Deficiency?

Because “vitamin D1” is not a supplement people consume today, deficiency symptoms are those of general vitamin D insufficiency:

• Bone pain or tenderness
• Muscle weakness or cramps
• Fatigue and low mood
• Frequent infections
• Slow wound healing
• Hair thinning
• Rickets in children (soft, deformed bones)
• Osteomalacia in adults

Types of Vitamin D at a Glance 

Name	Chemical Identity	Source	Status
Vitamin D1	Mixture of ergocalciferol + lumisterol	UV-irradiated ergosterol	Deprecated (not used)
Vitamin D2	Ergocalciferol	Fungi, yeast, fortified foods	Active supplement
Vitamin D3	Cholecalciferol	Animal skin, oily fish, sunlight	Active supplement (preferred)
Vitamin D4	22-dihydroergocalciferol	Rare, mostly research use	Minor role
Vitamin D5	Sitocalciferol	Plants (wheat pollen)	Experimental

Only D2 and D3 provide nutritional benefits.

What Does Modern Research Say About Lumisterol?

Here is where the story of vitamin D1 becomes interesting again. For nearly a century, lumisterol was dismissed as inert. That view has changed.

• Work led by Andrzej Slominski and colleagues has shown that lumisterol (L3) is metabolised by the CYP11A1 enzyme into a family of hydroxyderivatives.
• These hydroxylumisterols may act as partial agonists at the vitamin D receptor (VDR) and as inverse agonists at RORα/γ receptors, which are involved in inflammation and skin health.
• In human keratinocyte studies, lumisterol derivatives helped attenuate UVB-induced DNA damage, activated the NRF2 antioxidant pathway, and supported p53-mediated repair mechanisms.
• A 2024 study in the International Journal of Molecular Sciences also reported that certain lumisterol hydroxyderivatives may reduce melanoma cell proliferation in vitro, though clinical translation is still years away.

Reference: Photoprotective Properties of Vitamin D and Lumisterol Hydroxyderivatives (PubMed).

These findings do not revive vitamin D1 as a nutrient — but they do suggest that one of its two components (lumisterol) may have a future in dermatology and photobiology research.

Vitamin D1 vs D2 vs D3 — Quick Comparison 

Feature	Vitamin D1	Vitamin D2	Vitamin D3
Pure compound?	No (mixture)	Yes	Yes
Origin	UV-irradiated ergosterol	Fungi, yeast, plants	Animal skin, sunlight, fish
Currently used?	No	Yes	Yes (preferred)
Raises blood 25(OH)D	Not established	Yes	Yes, more effectively
Common in supplements	No	Yes	Yes

How Vitamin D1 Fits Into the Bigger Vitamin D Story (Step-by-Step)

• 1920s — Researchers discovered that UV-irradiated foods could cure rickets.
• 1931 — Askew’s team crystallised what they called vitamin D1 from irradiated ergosterol.
• 1932 — Windaus (Germany) and Bourdillon (UK) isolated the pure anti-rachitic sterol — later named vitamin D2 (ergocalciferol).
• Same period — The original D1 crystals were shown to be a 1:1 mixture of ergocalciferol and lumisterol.
• Post-1932 — The name vitamin D1 was officially dropped from scientific literature.
• 1936 — Windaus’s group characterised vitamin D3 (cholecalciferol) from animal sources.
• 2010s–2020s — Lumisterol is re-examined and found to have novel biological activity through CYP11A1 metabolism.

For a detailed timeline, the open-access review 100 Years of Vitamin D: Historical Aspects is highly recommended. For a deeper look at how the body actually produces and activates vitamin D today, see Vitamin D: Production, Metabolism, and Mechanism of Action — Endotext (NCBI).

Disclaimer: This article is for educational purposes only and is not medical advice. Consult a qualified healthcare provider before starting any vitamin D supplement or making changes to your nutritional intake.

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