Vitamin D acts more like a hormone than a vitamin, and a large share of men are low, especially indoors or in winter. Low levels are linked to lower testosterone, worse mood, and poorer recovery. It is cheap to measure and cheap to fix.
- It behaves like a hormone and touches testosterone, immunity, and mood.
- Deficiency is extremely common and usually silent.
- Sun exposure helps; most men also benefit from D3 (often paired with K2).
- Re-test after a few months to confirm you have actually reached target.