Vitamin D3
vitamin
ApprovedGeneral information about nutrients. No diagnosis, no medical advice. If you take medication, are pregnant or have a medical condition, talk to your doctor before taking supplements.
Overview
Vitamin D contributes to normal absorption/utilisation of calcium and phosphorus. Vitamin D contributes to the normal function of the immune system. Deficiency widespread, especially in northern latitudes.
Interactions
1,25(OH)₂D (active D3) upregulates TRPV6 calcium channels and calbindin-D9k in intestinal epithelial cells, dramatically increasing transcellular calcium absorption.
Active vitamin D (1,25(OH)2D) upregulates NaPi-IIb sodium-phosphate co-transporters in the intestinal brush border, increasing phosphorus absorption to maintain calcium-phosphorus homeostasis.
Vitamin D increases intestinal magnesium absorption, while magnesium is required for D3 activation. This bidirectional relationship means optimizing one improves the status of the other.
Vitamin D upregulates zinc transporters (ZIP4) in the intestinal epithelium, improving zinc absorption. Zinc in turn supports vitamin D receptor expression, creating a positive feedback loop.
Magnesium is required to convert vitamin D3 into its active form (calcitriol) via hydroxylation in the liver and kidneys. Low magnesium status impairs this conversion.
Vitamin D3 increases calcium absorption from the gut. K2 is needed to activate the calcium-binding proteins osteocalcin and matrix GLA protein.
Top 5 food sources
Expert opinions
Bryan Johnson Blueprint
Johnson takes 2,000 IU D3 daily paired with 600 µg K2-MK7. He titrates the dose from quarterly 25(OH)D labs, targeting the 40 to 60 ng/ml range cited by the Blueprint team. The D3 capsule is taken with breakfast alongside dietary fat for reliable absorption. Biomarker feedback, not a fixed dose, drives adjustments, with ionized calcium and PTH tracked to rule out hypercalcemia at higher blood levels.
Recommended dose: 2000 IU
Source: Blueprint Protocol
Dr. Andrew Huberman
Huberman takes 5,000 to 10,000 IU D3 daily in winter and 1,000 to 2,000 IU in summer, adjusted to labs. He describes D3 as a seco-steroid hormone rather than a classical vitamin. Vitamin D contributes to the normal function of the immune system. He combines it with K2-MK7 and magnesium. He emphasizes that supplementation cannot replace morning sunlight for circadian entrainment but fills the gap where UVB exposure is inadequate from autumn to spring.
Recommended dose: 1000–5000 IU
Source: Huberman Lab
NIH
NIH Office of Dietary Supplements sets the RDA at 600 IU (15µg) for ages 1 to 70 and 800 IU (20µg) for 71+, with a Tolerable Upper Intake Level of 4000 IU/day based on risk of hypercalcemia. Serum 25(OH)D is the standard marker: ≥20 ng/ml (50 nmol/L) is deemed sufficient for bone health, 30 to 50 ng/ml considered adequate by most clinical labs. At-risk groups include older adults, people with dark skin, limited sun exposure, or malabsorption.
Recommended dose: 600–800 IU
Source: NIH
Dr. Rhonda Patrick
Patrick advocates measuring 25(OH)D and supplementing 4,000 to 5,000 IU daily to reach 40 to 60 ng/ml. She highlights VDR polymorphisms that reduce responsiveness and the ligand role of D3 in regulating about 1,000 genes. Vitamin D contributes to the normal function of the immune system. She pairs it with magnesium (cofactor for hydroxylation) and vitamin K2.
Recommended dose: 4000–5000 IU
Source: FoundMyFitness
Current Research
Hypercalcemia risk rises from roughly 80 ng/ml 25(OH)D upward. Always co-supplement vitamin K2 and monitor serum calcium when dosing above 2,000 IU daily.
Source: Current Research
Dr. David Sinclair
Sinclair takes about 4,000 IU D3 daily as a foundational supplement, targeting serum 25(OH)D around 50 ng/ml. He pairs it with K2-MK7.
Recommended dose: ~4000 IU
Source: Dr. Sinclair Protocol
Dr. Strunz
Strunz targets 25(OH)D between 60 and 80 ng/ml and routinely prescribes 5,000 to 10,000 IU D3 daily, using higher loading doses in measured deficiency. He insists on the cofactors magnesium (for 25-hydroxylation) and vitamin K2-MK7 in every protocol. He views winter-only supplementation as insufficient because Central European UV levels are inadequate from October through April. He regards the official German cut-off of 20 ng/ml as systematic undersupply. Vitamin D contributes to the normal function of the immune system. Vitamin D contributes to the maintenance of normal bones.
Recommended dose: 5000–10000 IU
Source: Dr. Strunz
Expert profiles summarise publicly available statements. The named people do not cooperate with Stackwell and have not authorised these summaries. Not medical advice.
Most experts agree supplementation is needed. Dose depends on blood levels.