Vitamin K1 vs K2: Sources, Functions and Evidence

If you take warfarin or another blood thinner, read this first

Vitamin K changes how the blood thinner warfarin works. MedlinePlus (US) says that sudden changes in vitamin K intake can change the effect of the medicine, so keeping intake steady from day to day matters. [1] A small absorption study also warned that supplements giving 50 mcg a day or more of MK-7, one kind of K2, may interfere with oral anticoagulant treatment in a clinically relevant way. [2] Do not start, stop or switch any vitamin K product without telling your anticoagulation clinic, doctor or pharmacist. See Vitamins and blood thinners and medication interactions.

The short answer

Vitamin K1 and vitamin K2 are different natural forms of the same vitamin. Both help the liver make clotting proteins and both help activate proteins in bone and blood vessels. [3] There is no universal winner. Real differences exist in food sources and in how long each stays in the blood. Whether those differences change health outcomes is not settled, and no trial we found compared K1 and K2 head to head on fractures or heart events.

Evidence labels used on this page: established nutritional role, promising but limited, mixed, insufficient evidence, marketing claim. Proper evidence not found means we looked and found nothing usable.

What each form is

• K1 (phylloquinone) is made by plants and is the main form in most diets. [3]
• K2 (menaquinones, "MK-n") is a family of forms. Most are made by gut bacteria and found in fermented foods and animal products. [3]
• MK-4 and MK-7 are two K2 forms discussed often in research. MK-4 is the main K2 form in Western diets, and MK-7 is plentiful in natto, a Japanese fermented soybean food. [3]
• K3 (menadione) is a synthetic form that is not the same thing. Given by injection to infants it caused liver toxicity, jaundice and anemia, so it is no longer used to treat deficiency. [3]

Documented differences

A blood marker of vitamin K activity is not the same as fewer fractures or heart events.

What trials of each form found

Bone. A trial of 440 postmenopausal women with osteopenia gave 5 mg of K1 or placebo daily. Bone density did not differ after 2 years, though fewer clinical fractures were reported in the K1 group (9 versus 20). The authors said the study was not powered to test fractures. [4] A 3-year trial of 244 healthy postmenopausal women found that 180 mcg a day of MK-7 reduced the age-related decline in bone density at the lumbar spine and femoral neck, but not the total hip. [5] A later 3-year trial of 142 women with osteopenia, who also took vitamin D and calcium, found no difference in bone density between MK-7 and placebo. [6] A review of 16 K2 trials reported better lumbar spine density, and a fracture benefit only after one study was excluded. [7] Overall: mixed. The LPI at Oregon State University says trials have been inconclusive on whether extra K1 or K2 further reduces bone loss in people who already have enough calcium and vitamin D. [3]

Heart and arteries. In 365 older men with aortic valve calcification, 2 years of MK-7 plus vitamin D did not slow calcification compared with placebo. [8] In 159 people with chronic kidney disease, 400 mcg a day of K2 for a year did not improve arterial stiffness. [9] A 2026 trial of 180 people with symptomatic coronary disease found a significant difference in coronary calcium score after 2 years of MK-7 360 mcg a day, with a smaller rise in the MK-7 group. [10] This is one trial in one group. The LPI says evidence of benefit in preventing vessel calcification and heart events is limited. [3] Overall: promising but limited, and not shown for K1 versus K2.

Official intake levels

These figures are for population planning. They are not advice for any one person, and they do not make a supplement necessary. See RDA, AI, DV and UL explained.

Related pages

Vitamin K profile | Foods high in vitamin K | K2: MK-4, MK-7, bone and heart evidence | D3 with K2 vs D3 alone