What is vitamin K?

Vitamin K is a dietary supplement that may provide some benefits for bone health and vascular health.

Vitamin K

Vitamin K is a fat-soluble vitamin that is essential for the functioning of several proteins involved in blood clotting.* Vitamin K has also been identified as a key nutrient for bone metabolism, for the prevention of calcium buildup in the arteries and for promoting normal cell growth.*

Vitamin K is actually a family of similar substances that includes:

  • Vitamin K-1 (phylloquinone).
  • Vitamin K-2 (the menaquinones), which is subdivided into several forms, depending on the length of the molecule. The most common form of vitamin K-2 in humans is called MK-4, and the two forms of vitamin K-2 used in dietary supplements are MK-4 and MK-7.
  • Vitamin K-3 (menadione), which is a synthetic form.

What are the dietary sources of vitamin K?

Vitamin K-1 is found in algae and plants, particularly in green leafy vegetables. Vitamin K-2 as MK-4 is produced by bacterial fermentation in the intestinal tract and can be found in animal products, including meat, fish, eggs and cheese. Vitamin K-2 as MK-7 is also produced by bacterial fermentation. The most common source of MK-7 is a fermented soy product called natto. One study found that increased dietary intake of MK-7 in the form of natto resulted in increased levels of a protein called activated osteocalcin, which can help support healthy bones.* Eating foods rich in vitamin K-2 has been shown to decrease the risk of calcium buildup in the arteries (arterial calcification), which can lead to cardiovascular problems.

Ninety percent of the vitamin K in the average American diet is in the form of K-1, with the other 10 percent as K-2. To get significant amounts of K-2, dietary supplementation is often recommended.

Should I consider taking a vitamin K dietary supplement?

Vitamin K deficiencies are most commonly observed in children and older people. Although a vitamin K deficiency is not common in young adults, taking supplemental vitamin K can provide support for cardiovascular and bone health.* In the past, vitamin K-1 was typically the only form of vitamin K used in dietary supplements, such as in a multivitamin-multimineral product. However, during the past 10 years, propelled by research on the potential health benefits of vitamin K-2, both MK-4 and MK-7 have become available in dietary supplements.

How can a vitamin K dietary supplement affect my health?

Supplemental vitamin K can support your health in several ways:

  • Is necessary for normal blood clotting.*
  • Provides support for bone health, which is particularly important for young female athletes, since 16 to 22 percent of female high school athletes have low bone mineral density.*
  • Supports vascular health, which helps maintain blood vessel elasticity.*

How much supplemental vitamin K should I take?

The amount of vitamin K to take depends on its form and what you are taking it for. Studies show that vitamin K-2 in the form of MK-7 at doses as low as 180 micrograms (mcg) a day can provide significant support for bone health.* In one study, participants who took a dose of 1.5 mcg a day of MK-4 for six to 12 months maintained bone density better than the placebo group did.*

Doses of MK-7 as low as 180 mcg daily have also been shown to benefit vascular health.* In a three-year study of 244 women, vitamin K supplementation resulted in improved blood vessel integrity in the group taking vitamin K, compared with the group taking a placebo.*

Many nutrition experts suggest taking a vitamin K supplement at the same time as taking vitamin D because vitamin D increases calcium absorption.* Vitamin K can help keep calcium in your bones instead of collecting in the soft tissues such as blood vessels and kidneys.* In addition, studies indicate that the combination of vitamins D and K works better at protecting bones than does either one alone.*

Are there side effects from taking a vitamin K dietary supplement?

Even at very high doses, vitamin K does not increase blood clotting above normal amounts.

Is it safe to take a vitamin K supplement with medications?

The blood-thinning medication warfarin (Coumadin, Jantoven) works by interfering with the blood-clotting effect of vitamin K, and its effectiveness can be diminished by as little as 1 milligram of vitamin K. Therefore, using vitamin K in conjunction with warfarin is typically not recommended.

If you are considering taking a vitamin K dietary supplement, check with your health care professional first, especially if you are pregnant or have a health condition.

*These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure or prevent any disease.

Nov. 30, 2016