Vitamin D3
Cholecalciferol
Last reviewed: June 2026 · Medically reviewed by a licensed pharmacist
What it does
Vitamin D acts more like a hormone than a vitamin: it helps your gut absorb calcium for strong bones and tunes your immune system. Your skin makes it from sunlight, but office life, sunscreen, and northern winters mean most people run low, and low D often reads as fatigue or low mood. D3 is the form that raises your levels most effectively.
The science
Vitamin D3 regulates calcium absorption, immune modulation, and mood. Deficiency affects over 1 billion people globally. Most require supplementation in winter months.
Most relevant for
Indoor workers, darker skin tones, northern climates, and low energy or mood.
Key references
General wellness information, not medical advice. Consult your healthcare provider before starting any supplement. Build your personalized stack →