Vitamin K

Adults need one microgram a day of vitamin K for each kilogram of their body weight. So, someone who weighs 70 kilograms (around 11 stones) would need 70 micrograms a day of vitamin K, while a person who weighs 83 kilograms (around 13 stones) would need 83 micrograms a day. This guideline is based solely on maintaining normal blood clotting and doesn’t take into account the probable higher requirement for bone and other health benefits.

You should be able to get all the vitamin K you need by eating a varied and balanced diet. Any vitamin K your body doesn’t need immediately is stored in the liver, so you don’t need it in your diet every day.

The European Food Safety Authority (EFSA) have not set dietary reference values for vitamin K but suggest adequate intakes as follows:

• 10 micrograms for infants aged 7-11 months
• 12 micrograms for children aged 1-3 years
• 20 micrograms for children aged 4-6
• 30 micrograms for children aged 7-10
• 45 micrograms for children aged 11-14
• 65 micrograms for adolescents aged 15-17
• 70 micrograms for adults including for pregnant and lactating women

The 2000-2001 UK National Diet and Nutrition Survey Dietary (NDNS) looked at vitamin K intake in adults aged 19 to 64. The average intake was 67 micrograms per day. However, 59 per cent of people had intakes below the UK guideline for adequacy (one microgram per kilogram of body weight per day). The situation had worsened since an earlier 1986-1987 NDNS when the average intake was 72 micrograms a day and 47 per cent had intakes below the target. The fall in vitamin K intake is attributed to the lower consumption of cooked leafy green vegetables.

Vitamin K plays an important role in healthy 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 to death.

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 have been associated with an increased risk of osteoporosis and arthritis.

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 natto. The bacteria in your gut perform a similar function.

No, a healthy vegan diet containing the above foods on a regular basis will cover your needs – no need for supplements, just eat your greens!

If you take vitamin K supplements, don’t take too much as this might be harmful. The Department of Health says that taking one milligram or less of vitamin K supplements a day is unlikely to cause any harm.

However, if you take prescription medication that affects blood clotting (such as Warfarin), talk to your doctor about it as vitamin K can interfere with its efficacy. In 2012, a man taking anticoagulants (blood thinning medication) was admitted to hospital after doctors could not work out why his medication was not keeping his blood thin until they discovered he had been eating too many sprouts!

It’s important that you eat foods containing vitamin K. Make sure you eat similar amounts of them regularly.

Leafy green vegetables are by far the best source of vitamin K: spring greens, kale, spinach, cabbage, watercress, broccoli and Brussels sprouts all contain substantial amounts. Herbs and other vegetables (parsley, lettuce, asparagus, coriander, green beans, peas, cauliflower, runner beans, mustard and cress and leeks) provide an excellent source too. Plant oils are also a rich source of vitamin K (soya oil and rapeseed oil).

The Japanese food natto (made by fermenting cooked soya beans with Bacillus subtilis natto) has a very high content of K2 of about 1,000 micrograms per 100 grams. Meat, cereal and dairy products contain much lower amounts. Vitamin K is quite resilient and can withstand both cooking and freezing without huge losses.

Reduced blood clotting which may lead to easy bruising and prolonged bleeding, increased bone fragility and infections.

Vitamin K deficiency is very rare and usually only develops in people with severe liver or digestive tract diseases. People who take antibiotics for extended periods of time can experience a lack of vitamin K because antibiotics tend to kill the good gut bacteria that produce vitamin K2.

Source: Public Health England: McCance and Widdowson’s The Composition of Foods Integrated Dataset.

Vitamin K is a fat soluble vitamin, so combining leafy green vegetables with a little drizzle of soya or rapeseed oil might help you absorb it better.

Babies and vitamin K

Babies are born with low levels of vitamin K, but the amount is usually sufficient to prevent problems. However, some may be at risk of Vitamin K Deficiency Bleeding (VKDB), formerly known as Haemorrhagic Disease of the Newborn (HDN). This is a serious, but rare condition occurring in approximately one in every 10,000 babies. Because of this, the Department of Health recommends all babies are given vitamin K soon after birth, usually by injection but it can also be given by mouth.

Vitamin K1 and K2

Vitamin K1 (phylloquinone) is ubiquitous in the plant kingdom. It plays a role in photosynthesis and is structurally similar to the plant pigment chlorophyll. K1 is the major form of vitamin K in Western diets. The highest K1 contents (normally in the range 400-700 micrograms per 100 grams) are found in green-leafy vegetables. The next best sources are certain vegetable oils (soya, rapeseed and olive oil), which contain 50-200 micrograms per 100 grams and are also important contributors to dietary vitamin K intakes. Lower amounts of K1 are found in other vegetable oils, fruits, cereals, meat and dairy products.

Vitamin K2 (menaquinone) is the main storage form in animals. Most K2 is provided by the bacterial flora of the gut. Vitamin K2 is also found in fish, meat, liver and eggs, soya foods and some fermented dairy foods. In general, the UK diet is not rich in vitamin K2, Japanese diets contain higher amounts largely due to natto. The vitamin K2 family has several subtypes – MK-4 to MK-9, each with unique activities.

Anticoagulants

Daily supplements of up to 100 micrograms of K1, do not normally affect the activity of anticoagulant medications (warfarin) but supplements of menaquinone-7 (MK-7), as low as 10 micrograms may disrupt anticoagulant therapy. People taking anticoagulant medications (such as warfarin), should consult their doctor before taking vitamin K2 supplements.

Vitamin K and bone health

Many people now know that vitamin D contributes towards good bone health as it helps us absorb calcium. Some studies indicate that vitamin K may also help increase bone mineral density and reduce the risk of fracture.  Osteocalcin is a protein produced by osteoblasts during bone formation. Vitamin D promotes production of this protein, which then promotes the accumulation of calcium in the bones, but only in the presence of vitamin K. If there is insufficient vitamin K, osteocalcin is still produced but circulates in a form that has little or no biological activity.

Some evidence supports the idea that joint supplementation of vitamins D and K might be more effective than the consumption of just one or the other for bone and cardiovascular health. More studies are needed to confirm the role of vitamin K in bone health.

Vitamin K and cardiovascular heath

Vitamin K2 helps prevent calcium from being deposited in soft tissues, such as the kidneys and blood vessels. Calcium building up in blood vessels is dangerous as it can lead to the development of chronic diseases, such as heart and kidney disease. An optimal vitamin K intake is therefore important to keep the rate of inappropriate calcification as low as possible – calcium belongs in bones not arteries. But just because vitamin K2 may help reduce the risk of heart disease doesn’t mean that eating animal products high in vitamin K2 will also reduce the risk, since animal foods contain other substances that increase the risk of heart disease.

The consumption of a well-balanced diet is key for the prevention of chronic diseases. As more is discovered about how vitamins D and K work together, there are even more reasons to eat a healthy balanced diet including a wide variety of fresh fruit and vegetables for bone and cardiovascular health.

Malabsorption

Vitamin K deficiency may results from the malabsorption of fats due to diseases such as cystic fibrosis, coeliac disease, chronic pancreatitis or Crohn’s disease. Certain liver diseases (bile duct obstruction or primary biliary cirrhosis) can also lead to malabsorption and a deficiency in vitamin K.