Vitamin D3
vitamins
Essential fat-soluble vitamin produced by the skin in response to sunlight. Widespread deficiency in the UK, especially during winter months.
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Benefits
Dosage
Typical Dose
1,000-4,000 IU daily
Upper Limit
10,000 IU daily (short-term)
Timing
With a fat-containing meal for best absorption
Forms & Bioavailability
Cholecalciferol (D3)
High — preferred form, same as body produces
Ergocalciferol (D2)
Lower — plant-derived, less effective at raising blood levels
Side Effects
Interactions
Research Summary
Strong evidence for bone health and immune function. The VITAL trial (25,000 participants) showed reduced autoimmune disease risk. UK government recommends supplementation for everyone during autumn/winter.
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The Bottom Line on Vitamin D3
Vitamin D3 is well-researched with strong evidence supporting its primary benefits.It is most commonly used for bone health and calcium absorption and immune system support. As with any supplement, individual results vary. Start with the lower end of the dosage range and assess for 4-8 weeks before adjusting.
About Our Research
This profile is compiled from peer-reviewed research published on PubMed, the NIH Office of Dietary Supplements, and established nutritional science databases. Dosages reflect clinically-studied amounts from human trials where available. We update profiles as new research emerges. This is not medical advice — consult a healthcare professional before supplementing.
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Goal Guides for Vitamin D3
See how Vitamin D3 can help with specific health goals: