Short answer: vitamin D3 supports calcium absorption, bone health and immune function, and vitamin K contributes to normal blood clotting and to the maintenance of normal bones, which is why some formulas combine D3 with K2. Which strength suits you depends on your vitamin D blood level and your doctor's advice.
IU and micrograms
1 mcg of vitamin D = 40 IU. So 25 mcg = 1,000 IU, 125 mcg = 5,000 IU, 250 mcg = 10,000 IU and 1,250 mcg = 50,000 IU.
Examples from our labels
| Product | D3 per serving | K2 per serving | Label serving |
|---|---|---|---|
| NOW Vitamin D3 & K2 | 1,000 IU (25 mcg) | 45 mcg MK-4 | 1 capsule |
| NOW Mega D3 & MK-7 | 5,000 IU (125 mcg) | 180 mcg MK-7 | 1 capsule |
| Sports Research plant-based D3 + K2 | 10,000 IU (250 mcg) | 100 mcg MK-7 | 1 softgel |
| NOW Vitamin D3 10,000 | 10,000 IU | — | 1 softgel every three days |
| NOW Vitamin D3 50,000 | 50,000 IU | — | 1 softgel weekly |
MK-7 or MK-4?
Both are forms of vitamin K2 and the label names which one you get. In our examples MK-7 appears at 100 to 180 mcg in a once-daily serving, and NOW Vitamin D3 & K2 uses 45 mcg MK-4 per capsule. Follow the serving on the label.
Important
High strengths (10,000 and 50,000 IU) are taken at intervals as the label says, ideally based on a vitamin D test and your doctor's advice. Do not combine several high-strength vitamin D products (the Sports Research D3 + K2 label says so too). Anyone taking blood-thinning medication (such as warfarin) must ask their doctor before any product containing vitamin K.
Browse Vitamin D, Bone & joint or Immune. Supplements are not intended to diagnose or treat any disease.
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