Is VDR useful for fatigue?

Whether VDR (vitamin D receptor) genotyping is useful for fatigue is a common question, but the evidence is limited. VDR variants affect vitamin D signaling, and vitamin D deficiency is linked to fatigue. However, the effect of individual VDR polymorphisms on fatigue is small and inconsistent across studies. Most evidence comes from observational research, not from randomized trials showing that VDR-guided supplementation reduces fatigue. Fatigue is multifactorial (sleep, stress, diet, other genes), so a single VDR test is not clinically actionable. A blood vitamin D level is more informative. Be cautious of marketing that overstates VDR's role. Evidence: mechanistic/observational.