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Vitamin D3 (Cholecalciferol)
Hormone-like vitamin that regulates 1,000+ genes — deficiency is widespread and linked to poor immunity, depression, and bone loss.
What the evidence says
Vitamin D3 helped in about half (15/26) of the studies that measured an effect — promising, but not unanimous.
Most evidence is from high-quality meta-analyses and randomised trials published 2005–2026 with a typical study size of 871 participants.
Based on 72 studies · 28 meta-analyses · 14 RCTs · 290,341 total participants
Confidence
HighWhat the studies found
By outcome
See full supplement plans that include Vitamin D3.
Vitamin D3 has an evidence score of 9/10 — very strong evidence based on 72 indexed studies, including 26 meta-analyses. Hormone-like vitamin that regulates 1,000+ genes — deficiency is widespread and linked to poor immunity, depression, and bone loss.
The commonly studied dose of Vitamin D3 is 2000-4000 IU daily. Research points to an estimated optimal dose around 2000IU, with a minimum effective dose near 800IU. Individual response varies — start low and adjust.
The best time to take Vitamin D3 is in the morning. Take it with food. Vitamin D3 (cholecalciferol) is a fat-soluble secosteroid hormone precursor that requires bile acid emulsification and dietary fat for intestinal absorption via passive diffusion and cholesterol transporters (NPC1L1, SR-B1).
Last reviewed May 2026 · evidence from 40 studies · how we score
This information is for educational purposes only. It is not a substitute for professional medical advice. Always consult a qualified healthcare provider before starting, stopping, or changing any supplement or medication.
Vitamin D3 is a fat-soluble vitamin that functions as a hormone in the body. Deficiency is extremely common, especially in northern latitudes, and is linked to poor immune function, depression, muscle weakness, and bone loss. Optimal blood levels are 40-60 ng/mL.
Modulates both innate and adaptive immune responses
Regulates over 1,000 genes throughout the body
Essential for calcium absorption and bone health
How Vitamin D3 works — from molecular targets to health outcomes. Click an edge to see supporting research.This visualization is in beta — pathways are being refined and expanded.
2000-4000 IU daily
Loading: If severely deficient (<20 ng/mL): 50,000 IU weekly for 8 weeks under medical supervision
Take with food
| Form | Type |
|---|---|
| 💊D3 (cholecalciferol) softgel or liquid | Recommended |
| 💊D3 tablets | Alternative |
| 💧D3 drops | Alternative |
D3 is more effective than D2 (ergocalciferol). Oil-based softgels or liquid drops absorb best. Test blood levels after 2-3 months.
Minimum: 8 weeks
Optimal: 12 weeks
Cycling: Not required
Note: Take with a meal containing fat for best absorption. Morning is preferred as evening doses may interfere with sleep in some people.
You can get vitamin d3 from these foods and drinks. Doses are typical per-serving estimates — actual content varies by brand, brew, cooking, etc.
2000 IU per 3.5 ozs
3.5 oz cooked fillet. Wild Atlantic 1500–2000 mg omega-3 + 600–1000 IU vitamin D; farmed considerably lower.
660 IU per 3.75 ozs
One standard tin (3.75 oz) in oil or water, drained. The edible soft bones are why sardines are calcium-rich.
160 IU per 2 pieces
2 large egg yolks. Pasture-raised hens produce 3–4× more vitamin D. Whole eggs (white + yolk) add ~12 g protein.
1000 IU per serving
~15 min midday sun, light skin, arms + legs exposed. Highly variable: skin tone, latitude, season, sunscreen all matter.
100 IU per cup
1 cup. Vitamin D is added (fortification, US/Canada); raw milk has very little.
Meta-analysis showed 12% overall reduction in respiratory infections, with greater benefits in severely deficient individuals. Daily dosing more effective than bolus. Conservative estimate assumes most users not severely deficient.
Reduced frequency and severity of infections
Better mood and reduced seasonal depression symptoms
Reduced fatigue, especially if previously deficient
Improved strength and reduced muscle pain
Generally recommended; 1000-4000 IU is considered safe
Often need higher doses due to reduced skin synthesis
May need higher doses; melanin reduces vitamin D synthesis
May increase calcium levels
Steroids may reduce vitamin D absorption
Both metabolized by liver; monitor if using high doses — both affect lipid metabolism; may increase risk of myopathy through additive effects on muscle tissue
Tip: Don't exceed 10,000 IU daily without monitoring
Tip: Take with food
Both fat-soluble and support brain/immune health
Enhanced mood and immune support
Magnesium is required for vitamin D metabolism
Magnesium helps convert vitamin D to active form
Boron supports vitamin D metabolism
Enhanced vitamin D effectiveness and bone support
Both decline with age and support hormonal health
Comprehensive hormonal support
Both support muscle health in different ways
Comprehensive muscle support, especially in older adults
Both support bone health
Enhanced bone support
Both support bone health through different mechanisms
Enhanced bone density maintenance
Fat-soluble vitamins work together
Balanced fat-soluble vitamin status
D3 increases calcium absorption; K2 directs it properly
Essential pairing for bone health and preventing soft tissue calcification
Both support immune function
Enhanced immune system support
Vitamin D3 upregulates intestinal TRPV6 calcium channels and calbindin-D9k, dramatically increasing calcium absorption efficiency by 30-80%.
Superior bone mineral density, fracture prevention, and muscle function compared to either alone
Most standard MVIs contain only 400-800 IU vitamin D, which is below the therapeutic threshold for many adults. Supplementing separately with vitamin D3 fills this gap.
Optimal vitamin D status (50-80 nmol/L) for immune function, bone health, and mood regulation
Vitamin D3 is generally well-tolerated and considered safe for most healthy adults at recommended doses. The most commonly reported side effects are hypercalcemia (at very high doses), GI upset. Use caution if any of these apply to you: Hypercalcemia; Kidney disease (consult doctor); Sarcoidosis or other granulomatous diseases.
Vitamin B6
Likely helpsCofactor in 100+ enzyme reactions including serotonin, dopamine, and GABA synthesis — also lowers homocysteine levels.
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