Vitamin K is a category of nutrients that includes vitamin K1 and vitamin K2. Vitamin K2 is also a category, which contains different subtypes of vitamin K2. The form of vitamin K2 that has been studied the most for bone health is MK4. More than thirty years of research and over 25 clinical trials with more than 7000 volunteers conclude that MK4 (45 mg/day) supports healthy bone density and bone matrix, promotes healthy bone marrow, activates bone collagen genes and maintains strong bones as indicated by more than 70% fewer fractures in clinical trials. Unlike other forms of vitamin K, MK4 has also been shown to support cellular health and healthy cell division.

Adequate intake

The U.S. Institute of Medicine (IOM) has established the adequate intake of vitamin K to be 90 mcg per day for women and 120 mcg per day for men. Adequate intake (AI) is the amount of a nutrient believed sufficient to prevent a deficiency; however, adequate intake is not the optimal amount to promote health and is typically based on a limited number of health indicators.

For vitamin K, the adequate intake is based on the ability of vitamin K to promote healthy blood clotting. While vitamin K is essential for blood clotting, vitamin K has many other functions in the body. In addition to blood clotting, vitamin K is involved in growing healthy bones, producing healthy nerves and sustaining healthy blood production.

The amount of MK4 used in studies is 45-135 mg, which is 500 to 1,500 times greater than the IOM adequate intake. Thus, an important question is whether or not it’s safe to consume vitamin K at this high dose. The short answer is unambiguously, Yes. MK4 is safe even at doses much higher than the top amount used in clinical trials.

US Institute of Medicine (IOM) conclusion

The Tolerable Upper Limit (TUL) is the highest daily dose that is safe for almost all individuals in the general population to take on an ongoing basis. The IOM concluded that for natural forms of vitamin K, of which MK4 is one, there is no known TUL. This means that the IOM considers vitamin K to be extremely safe, even at very high doses.

US National Institutes of Health (NIH) conclusion

Another indicator of safety is the LD50. The LD50 is the amount of a substance that kills 50% of the laboratory animals. LD stands for “lethal dose.” The US National Institutes of Health (NIH) lists the LD50 for oral MK4 as  >5 grams/kg body weight. One gram is 1,000 times more than 1 milligram (mg). To make this more applicable to a real person, if someone weighs 120 pounds, the LD50 would be greater than 270 grams of MK4. That is 6,000 times more than the amount of MK4 used in in Osteo-K and Osteo-K Minis and most clinical trials (45 mg/day MK4).

Blood clotting safety studies

Since vitamin K is used in blood clotting, do high amounts of MK4 increase the risk for blood clots? In people with healthy blood clotting, hight dose vitamin K does not increase blood clot risk. Once the body has enough vitamin K for healthy blood clotting, the body can’t create excessive blood clots. It just doesn’t work that way. It’s like a conveyor belt. Once it’s going at full speed it can’t go any faster. The vitamin K simply goes on and does other beneficial things in the body.

Many studies have demonstrated the safety of MK4 on blood clotting. One clinical trial using 135 mg per day of MK4 concluded that blood clotting remained normal and no adverse reactions were observed. And of the dozens of clinical trials that used 45 mg/day of MK4 for as long as six years, none have reported any problems with blood clotting. In fact, the studies reported the complete absence of serious side effects.

Who should not take MK4?

People who take the drug warfarin (Coumadin) should not take MK4. Warfarin is a blood thinner that works specifically by blocking vitamin K’s actions in the blood clotting cascade. Providing vitamin K as a dietary supplement counteracts warfarin. People taking warfarin should absolutely not take MK4 and they shouldn’t take any vitamin K-containing products without first consulting their healthcare provider. 

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