gains kept after prohormone cycle

[SonofAtlas]

This is news to me.


Care to explain how vitamin D is a steroid?

It's an ergcolciferol, but is not a steroid.

Ergocalciferol is actually a form of Vitamin D, not the other way around.
"Steroid" is just a term denoting a terpenoid lipid with four fused carbon rings. There is a subfamily of steroids known as "secosteroids" that just have 3 fused rings and one broken ring. Vitamin D falls into this category.

The problem is people use the word "steroid" to denote chemicals like Winstrol. Steroid was a term initially coined in the 1920s to describe sterols, a family of chemicals that includes cholesterol.