Vitamins D3 & K2 by Dr. Mercola

Vitamin D3 and K2 suits adults whose Vitamin D, 25-Hydroxy is low or low-normal, especially if you get little sun, have darker skin, live at northern latitudes, or use sunscreen consistently. The 5,000 IU D3 here is a repletion-leaning daily dose for many, useful if your level hasn’t budged with 1,000–2,000 IU. K2 (MK-7) matters if you take calcium or have bone density concerns, because it helps steer calcium into bone. Higher body weight often requires more D3 to reach the same blood level; confirm with labs after 8–12 weeks.

Cholecalciferol (vitamin D3) is the form your skin makes from sunlight, and it raises Vitamin D, 25-Hydroxy more reliably than D2. As D3 rises, it increases calcium absorption and helps quiet parathyroid hormone (the signal that pulls calcium from bone). Vitamin K2 as MK-7 activates proteins like osteocalcin in bone and matrix Gla protein in arteries, which guide calcium into skeleton and keep it out of soft tissues. MK-7 has a longer half-life than K1 or MK-4, so a once-daily dose maintains steadier activation. D3 for infections was overhyped; large trials haven’t shown clear prevention.

Take one capsule daily with a meal that contains fat for better absorption. Recheck Vitamin D, 25-Hydroxy after 8–12 weeks to see if 5,000 IU is enough, then adjust. If your level is significantly low, short-term higher dosing under clinician guidance is common, then step down. You can take vitamin D3 and K2 any time of day; consistency beats timing. Pairing with magnesium is reasonable, since magnesium is a cofactor for vitamin D metabolism.

If you take warfarin (a vitamin K–antagonist blood thinner), skip vitamin K2 unless your prescriber plans frequent INR checks and dose adjustments. Other direct oral anticoagulants aren’t vitamin K–dependent but still warrant a quick check-in. Very high vitamin A plus high-dose D3 can raise calcium too much; keep vitamin A moderate. If your Calcium or PTH (parathyroid hormone test) is abnormal, get medical guidance before using higher-dose D3.

Avoid high-dose D3 if you have a history of high calcium, recurrent kidney stones, granulomatous conditions like sarcoidosis, or primary hyperparathyroidism until evaluated. Pregnancy and breastfeeding require individualized dosing; bring your labs to your obstetric clinician. If your Vitamin D, 25-Hydroxy is already high, this strength from Dr. Mercola is likely too much for maintenance—use a lower-dose D3 or take less frequently.