There's no such thing as vitamin D

What would you think if I told you vitamin D doesn't exist?

Because it doesn't.
By definition, a vitamin is something that your body cannot create.

You can and do create hormone D.

Before entering the body, this compound is known as a secosteroid hormone precursor.

Calcitriol, 1,25-(OH) D3, and calcidiol, 25-(OH) D3, are just two well-known forms of the twelve major human D3 forms - but all forms of D3 are precursors to hormones - never true vitamins.

Secosteroid D (whether D2 from plants or D3 from animals or skin) must undergo enzymatic conversion steps in the body - first in the liver to calcidiol (25-hydroxy D3) and then mainly in the kidneys to calcitriol (1,25-dihydroxy D3).

At no stage does D2 or D3 act like a vitamin - it does not serve as a coenzyme or simple nutrient. It functions as a prohormone immediately on entering the body.

The only reason it was historically called a vitamin is because early researchers didn't understand that it functions as a hormone. There is no valid scientific reason for labeling it a vitamin.

From the moment it is produced in the skin or ingested from food, it is part of a hormonal pathway - not a vitamin pathway.

If D3 is a hormone precursor rather than a vitamin, then supplementing it is not “topping up a nutrient” — it is interfering with a hormonal feedback system.

What you'll find in this article:

• Why D3 is a secosteroid hormone precursor, not a vitamin - and why the original labelling was a historical mistake nobody bothered to fix
• The 12 major forms of D3 in the human body and why your blood test only measures one or two of them
• What each of the 12 forms is, where it was found, and which one your doctor actually tests
• What synthetic D3 supplementation actually does to calcium, magnesium and your hormonal feedback loops
• Why adding calcium or K2 to "fix" the problem can actually worsen it
• The peer-reviewed conditions linked to long-term D3 supplementation - from arterial calcification to neurodegeneration
• Why a review of 290 studies and 172 trials concluded that low 25(OH)D is a marker of ill health, and what 25,871 people found on 2,000 IU a day in the VITAL trial
• Where death risk bottoms out in a study of 247,574 people: 20 to 24 ng/mL, below the line many labs call "low"
• What high doses do once they are in you: stored as plain D3, high calcium lasting months, and bone density falling by dose in a three-year trial
• Why a "low" 25(OH)D can sit next to a high active form in 100 patients, and the frail elderly group where the opposite happened
• What sun does that capsules don't: lower cholesterol in a trial of 100 men, and 0.6 to 2.1 more years of life expectancy in a 20-year Swedish cohort
• How to support real, usable hormone D year-round - even in the dark northern winter, without ever touching a synthetic capsule
• How to read your own lab sheet: the questions to ask about 25(OH)D, 1,25, ionized calcium, PTH and magnesium