Your VITAMIN D Isn't Working.... Here's Why

20.03.2026 Автор: Med Man You take vitamin D every day… but your levels won’t rise? Energy still low? Feeling worse after starting supplements? As an NHS GP, I see this constantly. Vitamin D deficiency that simply doesn’t shift — even with “high dose” tablets. In this video I explain why vitamin D might not be working for you. We cover D2 vs D3 (ergocalciferol vs cholecalciferol), correct vitamin D dosing (400 IU vs 1000–4000 IU), absorption issues, fat-soluble vitamins, obesity and vitamin D getting trapped in body fat, and why taking it with food matters. Then we get into the hidden mechanism most people miss: the magnesium connection. How magnesium activates vitamin D, what functional magnesium deficiency looks like, why blood magnesium levels can appear normal, and why some people develop cramps, palpitations, poor sleep, or a wired-but-tired feeling after starting vitamin D. Finally — should you take vitamin K2 with vitamin D? Is the theory actually plausible? If your vitamin D levels aren’t improving, or you feel worse on supplements, this will make sense of it.