What is it?
Vitamin K is a fat soluble vitamin named after the initial from the German word, koagulation. Ninety percent of our dietary intake is in the form of vitamin K1 with just 10% obtained in the form of K2. Probiotic bacteria in the gut also produce some K2 which we can absorb and use.
What does it do?
The liver uses K1 to make clotting proteins but K2 is the preferred form used in other parts of the body. Some vitamin K2 can be made from K1 within artery walls and internal organs but when K1 intakes are low, the liver holds on to its reserves so that little is available for conversion elsewhere.
Vitamin K2 is involved in making and activating a series of proteins that bind calcium. In the bones K2 regulates bone remodelling while elsewhere it helps to protect against unwanted calcification of tissues such as hardening of the arteries.
Osteoporosis: Bones contain two calcium-binding proteins (osteocalcin and MGP) whose activity depends on vitamin K2 to stimulate the formation of new bone. K2 is therefore vital for maintaining normal bones and protecting against bone thinning. It also works together with vitamin D3 to reduce the re-absorption of old bone. In postmenopausal women with osteoporosis, taking K2 supplements significantly improved bone mineral density of the spine compared with placebo.
Circulation: Within the arteries, vitamin K2 activates a protein (MGP) which inhibits calcification of artery walls – the only effective way to help prevent calcification within the circulation. By protecting against hardening of the arteries, K2 may help to protect against high blood pressure, coronary heart disease, stroke and dementia. When over 16,000 women were followed for around 8 years, every 10mcg increase in their dietary intake reduced their risk of coronary heart disease by 9%.
Research involving 36,600 people followed for 12-years also found that those with the highest intake of K2 were 29% less likely to develop peripheral arterial disease due to vascular calcification than those with the lowest intakes. No protective effect was found for dietary K1, however.
Where can we get it?
Vitamin K is present in our diet in two main forms. Most is obtained as vitamin K1 from plant sources such as cauliflower, broccoli and dark green leaves. Only around 10% is in the form of vitamin K2, which is found in animal-based foods such as liver, egg yolk and meats as well as foods fermented by bacteria such as probiotic yoghurt, cheeses and natto. Some vitamin K2 is also made by probiotic bacteria in the bowel, although the amounts absorbed are not enough to meet our needs – especially in older people.
How is vitamin K depleted?
It is depleted by low dietary intakes. Symptoms that may indicate deficiency include prolonged bleeding time, easy bruising, recurrent nose bleeds, heavy periods and diarrhoea.
The EU recommended daily amount is 75 mcg. The upper safe level for long-term use from supplements is suggested as 1000 mcg (1mg).
How to boost your vitamin K2 intake
Eat foods rich in K2 which is mostly obtained from liver, egg yolk, meats and bacterial fermented foods such as probiotic yoghurt, cheeses and natto. Dietary sources of vitamin K1 include cauliflower, broccoli, and dark green leafy vegetables such as spinach and some lettuces which provide more than 100 mcg K1 per 100g.
Supplements are usually taken at doses of 25mcg to 200mcg. Higher doses may be suggested for treating osteoporosis. Where possible look for supplements containing K2 rather than K1 to also obtain the circulatory benefits. Try Healthspan Vitamin K2, 60 capsules £9.95.
K2 is fat soluble and is best taken with meals for optimum absorption.
What to avoid
Seek medical advice before taking supplements containing vitamin K if you are taking warfarin as a blood thinning treatment (eg for a previous blood clotting disorder).
If you found X helpful, you’ll find more vitamin advice in our series The A to Z of Vitamins and Minerals on our Nutrition channel.Tags: Dr Sarah Brewer, nutrition, Rob Hobson, Vitamin K Last modified: June 9, 2022