rxr

vitamin d3 + vitamin a

Vitamin D and vitamin A act through partnered nuclear receptors. Vitamin D's active form binds the vitamin D receptor (VDR), which pairs with the retinoid X receptor (RXR) — whose ligand comes from vitamin A — to switch on genes for immunity, epithelial health, and bone. Adequate levels of both support this signaling, but at extreme doses they can work against each other for calcium and bone endpoints, where a controlled human study showed high preformed vitamin A blunting vitamin D's calcium response.