Saturday, May 18, 2024
HomeDiscoverVitamins & Minerals A-ZVitamin K – everything you need to know

Vitamin K – everything you need to know

What is vitamin K?

Vitamin K is a collective term for a group of vitamins that contain a functional group of 2-methyl-1,4-napthoquinone.  Some examples of this compound include phylloquinone (vitamin K1) and menaquinone (vitamin K2).

This vitamin is an essential vitamin, which means that it is not made in the body and it must be obtained through the diet.  It is also a fat-soluble vitamin, which means that it can be stored in the body for extended periods of time and it is not excreted out of the body as quickly as a water-soluble vitamin.

Where is it found?

Vitamin K is found in a variety of different foods.  Many green leafy vegetables, vegetable oils, and fruits contain high levels of phylloquinone.  Some foods that contain menaquinones include natto, which is made from fermented soybeans, as well as cheese, and other animal products. Some foods with the highest amounts include spinach, lettuce, and broccoli.

Vitamin K can also be found in supplements; it is available in a variety of different commercial multivitamin supplements as well as lone vitamin K supplement.  It is found in sufficient quantities in infant formulas.  Conversely, it is recommended that breastfed infants receive a one-time intramuscular injection after birth, and this is often given right after birth.

Why is it important?

This vitamin is essential for the function of an enzyme called vitamin K-dependent carboxylase, which is involved in blood clotting.  Therefore, this vitamin is important for the regular function of blood clotting and preventing internal bleeding.

Vitamin K is also known to potentially help regulate calcification of smooth muscle and cartilage; osteocalcin is a protein that is dependent on vitamin K levels and it is believed to help with bone remodelling.

What is the RDA for vitamin K

The recommended dietary allowance (RDA) is not established, so the following recommended intakes are based on the adequate intake (AI) instead.  These values are given by the National Institutes of Health (NIH), and the AI refers to the level that is assumed to ensure nutritional adequacy in the absence of a known RDA value.

The AI is 120 mcg daily for adult men and 90 mcg daily for women, including those who are pregnant and lactating.  The AI for teenagers between 14 and 18 years of age is 75 mcg, 60mcg for children between nine and thirteen years of age, 55 mcg for children between four and eight years, 30 mcg for toddlers between one and three years, 2.5 mcg for infants between seven and twelve months, and 2.0 mcg for infants under seven months of age.

There are many ways to meet this RDA through food or supplementation; three ounces of natto contains 708 percent of the AI, and a half cup of boiled collard greens or turnip greens contains 442 and 355 percent of the AI respectively.  Spinach, broccoli, and kale also contain large amounts; they all contain around 100 percent of the AI with each serving.

How much is too much?

Since it is a fat-soluble vitamin, it is not as easily removed from the body as a water-soluble vitamin.  However, it has a very low potential for toxicity; according to the Food and Nutrition Board (FNB), there are no known adverse effects related to excess consumption from supplementation or food sources.  For this reason, there are no currently established Upper Limit (UL) values. 

What are the benefits?

Vitamin K could potentially play a preventative role in a couple of different conditions.  Firstly, some studies suggest that higher intakes could be associated with increased bone health and a lower risk of fractures.  For example, one clinical trial found that postmenopausal women that received a low-dose menaquinone-7 (MK-7) vitamin K supplement daily for three years had lower rates of age-related height loss in the thoracic vertebrae compared to a control group. 

This makes sense because vitamin K is a vital cofactor for the production of osteocalcin, which plays a role in bone development.  However, other studies show no correlation between these factors; therefore, the evidence is inconclusive, and more research is needed to determine whether these results are relevant.

Next, vitamin K might potentially help reduce the risk of coronary heart disease.  One study of 4,807 people over the age of 55 in the Netherlands found that those who had the highest dietary intakes of vitamin K2, or menaquinone, had the lowest risks of dying from coronary heart disease compared to those with lower dietary intakes.

This makes sense because it is essential for the function of a protein called Matrix Gla-protein (MGP), and MGP is thought to help prevent vascular calcification.  Vascular calcification is a risk factor for coronary heart disease because it reduces the elasticity and flexibility of the arteries.  More research is needed to determine whether this is an effective measure of prevention.

Vitamin K deficiency

Although lone vitamin K deficiency is rare, some groups are at a higher risk of deficiency than others.  Newborn babies who did not receive supplemental vitamin K at birth are at increased risk of deficiency because it is not transferred well across the placenta.  In addition, people with gastrointestinal disorders and people who do not absorb fat as well, including those with cystic fibrosis, ulcerative colitis, and Celiac disease.  This is because these conditions can lower nutrient absorption, and vitamin K is absorbed best with dietary fat because it is a fat-soluble vitamin.

People on certain medications could have an increased risk of vitamin K deficiency.  For example, blood thinners such as warfarin (brand name Coumadin) may increase the risk of deficiency because they reduce the blood-clotting activity of vitamin K. Antibiotics can also potentially lower vitamin K levels because they can inactivate vitamin-K producing gut bacteria.  Finally, medications that lower fat absorption, such as the weight loss drug Orlistat, can reduce the absorption of fat-soluble vitamins including vitamin K.

Vitamin K deficiency can lead to a variety of potentially serious side effects, such as excessive bleeding from decreased blood-clotting ability, as well as reduced bone mineralization and an increased risk of osteoporosis.

Vitamin K supplementation

Vitamin K deficiency is generally treated by supplements, taken either orally or by injection.  Deficiency can also be prevented by meeting your nutritional needs through the diet or taking supplements.

If you think you have a deficiency or are at an increased risk, consider getting your blood levels tested.  As always, consult your doctor before you begin taking any vitamin or mineral supplement, to make sure your medications or health conditions don’t make it a serious risk.

Reference List

Bradford, A. (2015, August 18). Vitamin K: Sources & Benefits. Retrieved November 22, 2020


Centers for Disease Control and Prevention – Vitamin K. (2019, December 14). Retrieved

            November 22, 2020, from


Demer, L.L., Tintut, Y. (2008). Vascular calcification: pathobiology of a multifaceted disease.

            Circulation 117(22), 2938-2948. Doi: 10.1161/circulationaha.107.743161

Eden, R.E., Coviello, J.M. (2020). Vitamin K Deficiency. StatPearls [Internet]. Retrieved

            November 22, 2020 from

Geleijnse, J.M., Vermeer, C., Grobbee, D.E., et al (2004). Dietary intake of menaquinone is

            associated with a reduced risk of coronary heart disease: the Rotterdam Study. J Nutr

            134(11), 3100-3105. Doi: 10.1093/jn.134.11.3100

Gundberg, C.M., Lian, J.B., Booth, S.L. (2012). Vitamin K-dependent carboxylation of

            osteocalcin: friend or foe? Adv Nutr 3(2), 149-157. Doi:

Knapen, M.H.J., Drummen, N.E., Smit, E., Vermeer, C., Theuwissen, E. (2013). Three-year low-

            dose menaquinone-7 supplementation helps decrease bone loss in healthy

            postmenopausal women. Osteoporosis Int 24(9), 2499-2507. Doi: 10.1007/s00198-013-


Office of Dietary Supplements – Vitamin K. (2020, June 3). Retrieved November 22, 2020, from



Please enter your comment!
Please enter your name here

Latest News and Articles


Stay Connected

Article of the month

Recognizing HIE: A Call for Advocacy

Have you heard of HIE? It’s the second leading cause of infant mortality and lifelong disability worldwide. 2-3 per 1,000 live births in high-income...

Joke Of The Day – May 18

The man told his doctor that he wasn’t able to do all the things around the house that he used to do. When the examination...


error: Content is read-only and copy-protected.