Vitamin D-3 & K-2 by Now Foods

This is a maintenance-level vitamin D3 with a modest amount of vitamin K2 added. It suits adults whose Vitamin D (25-hydroxy) is in range or slightly low and who want the two vitamins that handle calcium in one capsule, particularly people who also take calcium or are thinking about bone health as they age. If your level is clearly low, you will need more vitamin D than this for a while. It is not for anyone taking warfarin unless the prescriber agrees.

Vitamin D3 (cholecalciferol) raises the amount of calcium you absorb from food. Vitamin K2 switches on the proteins that deal with that calcium: osteocalcin, which binds calcium into bone, and matrix Gla protein, which helps keep calcium from settling in artery walls. The K2 here is menaquinone-4 (MK-4), a form the body clears within hours, unlike the longer-lasting MK-7. That pairing is the logic behind the label's bone and cardiovascular support statements; trials on whether added K2 changes fracture or heart outcomes are mixed.

Each capsule provides 1,000 IU (25 mcg) of vitamin D3 and 45 mcg of vitamin K2 as MK-4. The label directs 1 capsule 1 to 2 times daily with food; a meal that contains fat suits it, because both vitamins are fat-soluble. One capsule a day is the usual maintenance choice, and a second is worth agreeing with your clinician against your blood level. Count the vitamin D in any multivitamin or calcium product you also take. Recheck Vitamin D (25-hydroxy) after 8–12 weeks to see whether the dose is holding your level.

The label says to consult a physician before use if you take any anticoagulant, such as warfarin (Coumadin) or heparin. Vitamin K works against warfarin and other vitamin K antagonists, so do not start, stop or change this product without your prescriber: even a small change in daily vitamin K intake can shift your INR. Newer anticoagulants such as apixaban and rivaroxaban do not act through vitamin K, but tell your prescriber anyway. For the vitamin D, avoid unsupervised use with a history of high calcium, kidney stones, hyperparathyroidism, sarcoidosis or significant kidney disease; thiazide diuretics raise the chance of high calcium. Orlistat and bile acid sequestrants reduce absorption of both vitamins. The label is for adults only; if you are pregnant or nursing, check with your clinician first.

Vitamin D levels rise gradually over 2–3 months, and you will not feel K2 working. Bone changes take a year or more to show on a scan and depend more on calcium, protein, exercise and overall vitamin D status than on any one capsule. Compared with D3 alone, the difference is the added K2; compared with MK-7 products, MK-4 is shorter-acting. If your vitamin D is low, a higher-strength D3 for repletion makes more sense first.