Vitamin D3
Vitamin D acts more like a hormone than a vitamin, influencing bone health, immune function and muscle. Deficiency is widespread anywhere with real winters or indoor lifestyles.
Effective dose
1,000–4,000 IU per day for most adults. A blood test is the only way to dose precisely.
Timing
With a meal containing fat, any time of day.
What it is
A fat-soluble vitamin your skin makes from sunlight and that appears in very few foods.
How it works
It regulates calcium absorption for bone, supports immune signalling and is involved in muscle function. Correcting a deficiency can produce a noticeable difference in energy and illness frequency.
What the research shows
- Deficiency is associated with reduced muscle function, more illness and worse bone health.
- Supplementing helps clearly when levels are low; benefits are minimal when they are already sufficient.
Best for
Forms to look for
- D3 softgels
- D3 with K2
- Liquid drops
What to watch out for
Very high long-term doses can cause calcium problems. Test rather than guess above 4,000 IU per day.
Sourcing partners
Coming soonWe are onboarding a short list of vetted suppliers for vitamin d3, each with published certificates of analysis and third-party identity testing. Direct purchasing will open here once those partners are live.
FAQs
D2 or D3?
D3. It raises and maintains blood levels more effectively than D2.
Related on SportsNutrition.com
Educational information only, not medical advice. Talk to your physician or a registered dietitian before starting a supplement, especially if you are pregnant, nursing, managing a health condition, or taking medication.