What is vitamin K, and where to find it on a vegan diet

Veronika Powell lets the information flow on a little vitamin that’s a bit of a clot…

Often overlooked, vitamin K plays an important role in blood clotting. The letter K is derived from the German word, koagulation (blood clotting), and is essential for wound healing when we injure ourselves. Our blood needs to start clotting very quickly otherwise we might bleed indefinitely.

Another important function of vitamin K is in keeping our bones healthy and strong, being crucial to bone cell maintenance and bone protein formation. Low levels of this little-talked about vitamin have been associated with an increased risk of osteoporosis and arthritis.

Where do we find it?

There are two types of vitamin K – K1 and K2. Vitamin K1 is found in leafy green and some other vegetables, while vitamin K2 is usually found in small amounts in animal-based foods, as well as being produced by bacteria. These bacteria convert plant-sourced K1 into K2. A good example is bacillus natto, which is used in the fermentation of soya beans to produce tempeh. Your gut bacteria perform a similar function.

Vitamin K is a fairly stable nutrient so its content decreases only slightly with cooking. It is also fat soluble, which means that eating a little fat in a meal containing vitamin K will help its absorption, but a tiny amount is sufficient. Good sources of vitamin K include kale, spinach, Brussels sprouts, Swiss chard, green beans, asparagus, broccoli, collard greens, thyme, romaine lettuce, sage, basil, oregano and cabbage.

Vitamin K deficiency is very rare and usually only develops in severe liver or digestive tract diseases. Sometimes, newborn babies can temporarily suffer from it, as they need their body stores to build up and, in extreme cases, a vitamin K injection may be needed. People who take antibiotics for extended periods of time can also experience a lack of vitamin K, because antibiotics tend to kill the good gut bacteria that produce vitamin K2.

How much is enough?

Adults need about 0.001mg a day for each kilogram of their body weight. So if you weigh 65kg, it’s 0.065mg of vitamin K a day. It’s very little and just one serving of kale, broccoli, Brussels sprouts or spinach will comfortably cover your needs.

It’s easy to get the vitamin K you need simply by eating a varied vegan diet. Any your body doesn’t use up is stored in the liver, so even if you have a couple of not-so-healthy days, you don’t need to worry about it. There’s no upper limit to vitamin K intake, because there are no known adverse effects from high intakes. However, if you take medication that affects blood clotting (eg Warfarin), talk to your doctor about it, as vitamin K can interfere with its efficiency.

Vitamin K in foods

Recommended intake is 0.001mg/kg of body weight, so on average, we need about 0.06-0.09mg per day.

Viva! is a charity working to promote veganism and to end animal suffering. Veronika Powell is a health campaigner at Viva! specialising in the links between diet and its impact on our health. Veronika is a biologist and qualified teacher. www.viva.org.uk