Vitamin K2: the definitive guide

Vitamin K2: the definitive guide

Vitamin K2 is known to be vital for bone and cardiovascular health. In this article, we take a look at the discovery of Vitamin K and how this nutrient can help you to maintain your quality of life as you get older.

The history of vitamin K

Professor Henrik Dam, Danish scientist

Vitamin K was discovered in the early 20th century by Professor Henrik Dam, a Danish scientist. He noticed that normal blood clotting required more than just vitamins A, C and D. He also discovered that bleeding problems in animals could be cured with seeds and cereals, and speculated that there was an extra vital nutrient present in these foods.

He called this the ‘koagulations vitamin’ – vitamin K – and found that it was present in a variety of foods, including leafy green vegetables, liver and fermented bran or fishmeal. This discovery earned Henrik Dam and Edward Doisy, who researched the chemistry of vitamin K, a Nobel Prize in Physiology or Medicine.

At the same time Henrik Dam was performing his experiments, an American dentist called Weston Price was busy exploring the effects of different diets around the world. He found that the unknown nutrient, vitamin K, appeared in foods uncommon in the western diet and seemed to improve the health of the nations who ate these foods.

In the 1950s, scientists realised that there are actually two types of vitamin K, which affect different areas of health.

What is the difference between vitamin K1 and vitamin K2?

There are two types of vitamin K. Both of these activate proteins in the body as part of important biological processes.

The two types of vitamin K are:

  1. Vitamin K1 (phylloquinone): responsible for normal coagulation (blood clotting).

  2. Vitamin K2 (menaquinone): the most important forms are MK-4 and MK-7.

A vitamin K1 injection is given to newborn babies to prevent a rare bleeding disorder. It is easy to get enough vitamin K1 from a normal, healthy diet by eating a few leafy green vegetables such as broccoli and a little vegetable oil. Supplementation does not generally improve health. However, western diets are low in vitamin K2. It is found in particularly high concentrations in fermented foods such as natto, a traditional Japanese dish made with soybeans.

Natto on rice, a traditional Japanese dish made with soybeans

With renewed interest in vitamin K2 in the 1990s, numerous studies were commissioned in Japan and around the world. These studies found that the health benefits of vitamin K2 include:

  • strengthens bones by regulating calcium in the blood

  • improves cardiovascular health

Note that these effects are associated with vitamin K2, not vitamin K1.

Calcium is essential for bone health, and if you are deficient it will increase your risk of developing osteoporosis. Vitamin K2 regulates calcium in the blood by ensuring that it is moved from the blood into the bones, which strengthens them.

Studies using vitamin K2 have shown that it increases bone quality. A 2017 journal found that people taking a combined vitamin D, calcium and K2 supplement were 25% less likely to suffer a fracture during their lifetime. In Japan, where many of the vitamin K2 studies have been conducted, it is a standard recommendation for people with osteoporosis.

Having weaker bones increases the chance of fracture if someone were to fall. Vitamin K can help by making bones stronger. Dr Nicholas Shenker, Consultant Rheumatologist, Addenbrooke's Hospital

Why can’t you just take calcium?

While calcium is the key to stronger bones, if you are not getting enough vitamin K2 then increasing your intake of calcium can actually be counterproductive.

If you do not get enough K2, excess calcium will remain in your bloodstream, leading to calcification of the arteries, which can cause high blood pressure and even heart disease.

Observational studies using the data of tens of thousands of people have shown that those with high intakes of vitamin K2 are far less likely to die of heart disease – in one study, they were 57% less likely.

It is also important to get enough vitamin D, as a vitamin D deficiency makes it harder for your blood to absorb calcium; some vitamin K2 supplements also contain vitamin D for this reason. The NHS recommends that all adults in the UK take a vitamin D supplement in the Autumn and Winter.

How much vitamin K2 do you need a day?

Adults should ensure they are getting between 100 and 300 micrograms of vitamin K2 per day. Children under 12 need just 45 micrograms per day. People with particular medical conditions may need more, as recommended by their doctor.

There are no known serious side effects from taking too much vitamin K2. However, it is sensible to stick to the recommended intake.

What are the best sources of vitamin K2?

Vitamin K2 is largely absent from the western diet, so getting enough can be difficult. A dietary supplement may be a good option, especially for people who do not consume meat or dairy products.

Do you need more vitamin K2 as you get older?

Men begin to lose bone density at age 55, and women begin during menopause due to the decline in oestrogen production. For this reason it is important to ensure you are getting enough calcium to your bones as you get older, so vitamin K2 does become more of a priority. Women should begin in middle age, before the menopause kicks in and causes bone loss faster.

In one 2013 study, it was found that children and adults over 40 were most likely to be deficient in vitamin K2, so children may also benefit from a change in diet or even a supplement of suitable strength.

Can you take warfarin and a vitamin K2 supplement?

It is known that foods rich in vitamin K2 can have a major effect on blood clotting. If you are on a blood thinner such as warfarin you should monitor your dietary intake of vitamin K2. Many vitamin K2 supplements should not be taken with warfarin.

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