Vitamin D3 (Cholecalciferol)
Supports calcium absorption and bone mineralization; UL is 4,000 IU/day for adults.
By Suplagen Team · Updated
What it is
Vitamin D is best established for bone health and correcting low vitamin D status; many other claimed benefits are more inconsistent.
How it works
Converted to active metabolites that regulate calcium/phosphate handling and gene transcription via vitamin D receptors.
What the evidence says
Strong for bone and deficiency correction; broader benefits are more variable across trials.
How much to take
The catalog range is 800 to 2,000 IU daily, with a 4,000 IU ceiling. The evidence is strong for bone and for correcting deficiency; broader claims are more variable across trials, so the range isn't a launchpad for megadosing.
Higher doses long-term deserve a 25(OH)D blood test rather than guesswork. Toxicity is rare, and when it happens it comes from supplements, not sun.
When and how to take it
With a meal that contains fat; D3 is fat-soluble and absorbs poorly without it. Morning or midday, once daily.
Pair it with K2, which the catalog calls essential for long-term D3 use, and watch combined high doses with calcium.
Who should skip it
Hypercalcemia rules it out; granulomatous disease and severe kidney disease are cautions. Interactions: orlistat (moderate; it blocks fat absorption, and D3 along with it) and thiazide diuretics (moderate; they raise calcium). Pregnancy is listed as safe.
Safety Notes
- Adult UL is 4,000 IU/day; toxicity is typically from excessive supplementation.
- Use caution with: hypercalcemia, granulomatous disease (caution), severe kidney disease (caution).
- orlistat: Reduces absorption of fat-soluble vitamins.
- thiazide diuretics: May increase hypercalcemia risk when combined with vitamin D.
Timing With Other Supplements
- Calcium (Supplemental): Useful for bone, but combined high intakes can raise hypercalcemia/hypercalciuria risk.
Common questions
How much vitamin D3 should I take daily?
800 to 2,000 IU with a fatty meal for most adults. The ceiling is 4,000 IU; above the range, test your 25(OH)D first.
Should vitamin D be taken with fat?
Yes. It's fat-soluble, so a meal with eggs, oil, or dairy makes the difference between absorbing the dose and wasting much of it.
Do I need K2 with vitamin D?
The catalog calls K2 essential for long-term D3 use: D3 raises calcium absorption, and K2 helps direct that calcium to bone. The pairing explained.