Vitamin K2: Menaquinone, Not K1

Vitamin K2 refers to menaquinones, designated MK-4 through MK-13 by the length of their side chain; MK-4 and MK-7 are the best studied and the ones you'll see on labels. They occur naturally in fermented foods — natto is especially rich — and in modest amounts in animal foods. Supplements state both the subtype (MK-4 or MK-7) and the microgram amount, which is what makes one K2 product comparable to another.

Vitamin K is a coenzyme for the enzyme that activates vitamin-K-dependent proteins. Two of those are osteocalcin, involved in bone metabolism, and matrix Gla-protein, studied in the context of normal calcium handling — the basis for K2's association with bones. Prothrombin, another K-dependent protein, is central to normal blood clotting, which is the long-established role of vitamin K overall.

MK-7 generally stays active in the body longer than MK-4, so it's often dosed once daily at lower microgram amounts, while MK-4 tends to appear at higher doses. Neither is automatically "better" — the subtype and amount on the label are what let you compare. K2 is fat-soluble, so it's typically taken with a meal that contains some fat.

At Monthlees, vitamin K2 appears in the Testosterone Foundation Smart Stack, which includes both the MK-4 and MK-7 forms of K2 alongside its other ingredients. As with any K2, the subtype and microgram amount are the details worth reading on the label, and because it's fat-soluble it's best taken with a meal that contains some fat. One general caution applies to vitamin K in any form: if you take a blood thinner such as warfarin, keep your vitamin K intake consistent and talk to your healthcare provider, because vitamin K interacts with these medicines.