Vitamin D3

Tier 1 — strong evidence · Bone · Immunity · Muscle

The preferred form of supplemental vitamin D, converting more efficiently to active 25(OH)D than D2 (2023 van den Heuvel meta-analysis, 20 comparative studies, PMID 37865222). Essential for calcium absorption, bone density, muscle function, and immune regulation. The VITAL RCT (25,871 participants, 5.3 years) found 2,000 IU/day reduced confirmed autoimmune disease incidence by 22% (HR 0.78; Hahn 2022 BMJ, PMID 35082139). About 40% of adults worldwide are deficient, especially those with limited sun exposure, darker skin, or obesity. Test serum 25(OH)D before supplementing. UL is 4,000…

Dose: 1,000–2,000 IU/day for maintenance in adults; 2,000–4,000 IU/day to correct deficiency under medical guidance. Target serum 25(OH)D: 40–60 ng/mL. Pair with vitamin K2 (100–200 mcg MK-7) when supplementing long-term.