Check before you startThis one has documented interactions with medication classes where the consequences are serious. If you take any prescription medicine, run it past a pharmacist before starting.
How long to take it
Ongoing. This is a structural gap, not a phase — most people take it for life, ideally with a blood level checked yearly.
Who it's actually for
Almost everyone at northern latitudes, anyone mostly indoors, darker skin tones, older adults, and those who cover up.
Safe upper limit
Verified100 mcg / 4,000 IU per day
Fat-soluble and stored. Sustained excess raises blood calcium, which can damage kidneys and calcify soft tissue.
UL ranges 25–100 mcg (1,000–4,000 IU) by age; 100 mcg/4,000 IU is the adult figure.
Interactions to know about
- Thiazide diuretics — Hydrochlorothiazide, indapamide
- Digoxin — Heart rhythm medication
- Corticosteroids — Prednisolone, dexamethasone
- Statins — Atorvastatin, simvastatin, rosuvastatin
Other supplements:
Run your full list through the interaction check.
Practical notes
- Take with a meal containing fat — absorption roughly doubles.
- Pair with K2 so the calcium it mobilises goes to bone, not arteries.
- Weekly dosing works as well as daily if that's easier to remember.