Vitamin K2 MK-7 vs MK-4: How the Two Forms Differ

Vitamin K contributes to the maintenance of normal bones. But not all K2 is the same. The two main forms—menaquinone-4 (MK-4) and menaquinone-7 (MK-7)—have distinct properties that affect how they work in the body. Understanding these differences can help you make an informed choice for your health.

Vitamin K is a fat-soluble vitamin essential for blood clotting and bone metabolism. It exists in two natural forms: K1 (phylloquinone) found in green leafy vegetables, and K2 (menaquinone) produced by bacteria and found in fermented foods like natto. K2 is further divided into subtypes based on the length of their side chain, with MK-4 and MK-7 being the most studied.

Chemical Structure and Sources

MK-4 has a short side chain (4 isoprene units) and is found in animal products like liver, egg yolks, and butter. It can also be converted from vitamin K1 in the body, though this conversion is limited. MK-7 has a longer side chain (7 isoprene units) and is primarily found in natto (fermented soybeans) and some cheeses. The longer chain gives MK-7 a longer half-life in the bloodstream.

Absorption and Bioavailability

MK-7 is absorbed more efficiently and remains active in the body for much longer than MK-4. A study published in Osteoporosis International found that MK-7 has a half-life of about 3 days, while MK-4's half-life is only about 1-2 hours (PubMed). This means MK-7 can maintain steady levels with a single daily dose, whereas MK-4 requires multiple doses throughout the day.

Dosage and Frequency

Because of its short half-life, MK-4 is typically taken in higher doses (e.g., 45 mg per day divided into three doses) in clinical studies. MK-7 is effective at much lower doses (e.g., 45–100 mcg per day) due to its superior bioavailability. A common supplement dose is 100 mcg of MK-7 once daily.

Both forms activate osteocalcin, a protein that binds calcium to the bone matrix. However, research suggests MK-7 may be more effective at maintaining bone mineral density. MK-4 has also shown benefits, but requires higher doses.

Vitamin K2 activates matrix Gla-protein (MGP), which inhibits calcium deposition in arteries. This may be due to MK-7's longer circulation time, allowing more sustained activation of MGP.

Both forms are generally well-tolerated. However, vitamin K can interfere with anticoagulant medications like warfarin. If you take blood thinners, consult your doctor before supplementing with any form of vitamin K. MK-7 has been reported to cause mild gastrointestinal issues in some individuals at high doses.

MK-7 stays in the blood longer than MK-4, so it is taken once a day.

Vitamin K contributes to the maintenance of normal bones and to normal blood clotting. When choosing a supplement, look for a reputable brand that provides MK-7 in a fat-soluble form (e.g., with oil) for best absorption. As always, speak with a healthcare professional before starting any new supplement, especially if you take medication.