Vitamin D (synthesis, transport, receptor)

A genome-wide study in around 34,000 people found three main loci whose most unfavourable combination more than doubles the insufficiency risk (top versus bottom genotype quartile, OR ≈ 2.47; Wang 2010). rs2282679 (GC, vitamin D binding protein) is by far the strongest hit on 25(OH)D (p ≈ 10⁻¹⁰⁹) and lowers the level in the effect allele. rs12785878 near DHCR7 reduces the precursor available in the skin for D₃ synthesis. rs10741657 near CYP2R1 brakes activation in the liver. rs6013897 near CYP24A1 affects degradation. At the end of the chain the VDR receptor (FokI rs2228570, BsmI rs1544410, ApaI rs7975232, TaqI rs731236) modulates how strongly the cell responds.

Genotype and blood level answer different questions: the markers describe a predisposition to somewhat lower or higher levels and a differing sensitivity of the cell, while the measured 25(OH)D value shows the actual state. Someone genetically prone to low vitamin D reaches good levels less often at the same sun and intake. None of these variants alone necessitates supplementation.

The level loci (GC, DHCR7, CYP2R1) are very well documented; the VDR receptor associations remain weaker and inconsistent. For depth see the dedicated pages on GC (binding protein) and VDR (receptor). Genome shows all markers as technical evidence.