Vitamin D3 + K2
Critical when sun exposure is limited; supports mood and bones.
- Typical dose
- 2000–4000 IU50–100 mcg
- When to take
- Morning
- Onset
- 4–8 weeks to raise serum 25(OH)D; get a blood test before and after
What it does
Benefits
- Supports bone density by regulating calcium absorption
- Modulates immune function; deficiency linked to frequent infections
- May improve mood, especially in winter months
- K2 directs calcium into bones and away from arteries
The science
How it works
Vitamin D3 (cholecalciferol) is converted to calcidiol in the liver, then calcitriol in the kidneys — a hormone that regulates hundreds of genes. K2 (MK-7) activates osteocalcin, which binds calcium into bone matrix.
Getting it right
Dose & timing
Dose guidance
2000–4000 IU/day is a common maintenance range for adults with limited sun. Deficient individuals may need 5000+ IU under medical guidance. Target serum 25(OH)D of 30–50 ng/mL.
Best time to take
Take with the largest fatty meal of the day — it's fat-soluble.
Is it for you?
Who should (and shouldn't) take it
Good for
- Limited sun exposure (indoor work, northern latitudes, dark skin)
- Over 50 (skin synthesizes less efficiently)
- Bone density concerns
- Frequent colds
Skip or ask a doctor if
- You have hypercalcemia or sarcoidosis
- You're on high-dose warfarin (K2 interacts)
- You take thiazide diuretics (monitor calcium)
Know before you start
Side effects & safety
- Rare at sensible doses
- Hypercalcemia with extreme doses (10,000+ IU/day sustained)
- Nausea or constipation from excess
Shopping guide
Forms & what to look for
- D3 (cholecalciferol)
Preferred — better raises blood levels than D2
- D3 + K2 (MK-7) combo
Synergistic for bone and arterial health
- Liquid drops
Flexible dosing; good for kids
Combining
Stacks well with / avoid pairing
Stacks well with
Common questions
FAQ
Do I need K2 with my D3?
Not strictly required, but K2 helps direct the extra calcium D3 absorbs into bones rather than soft tissue. Cheap insurance.
Can I just get sun instead?
10–30 min midday sun on arms/legs a few times a week works for many — but skin tone, latitude, sunscreen, and season all reduce synthesis.
Is 5000 IU safe?
For most adults, yes — but get a 25(OH)D test to confirm you need it and aren't overshooting.
References
Sources & further reading
Educational only, not medical advice. Check with a clinician before starting anything new, especially if you're on medication or pregnant.
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