Vitamin K is a name given to a group of fat-soluble vitamins. They are considered essential cofactors in humans that are involved in blood clotting and calcium balance. The original term vitamin “K” comes from the K in the German word Koagulation meaning the ability to clot blood or prevent bleeding.
There are two types of vitamin K, vitamin K1 (phylloquinone) and vitamin K2 (a series of menaquinones). Menaquinones are numbered MK-4 through MK-13, based on their chemical structure. K1 can be converted to K2 in the gut with microbiota. However, only 20% of K1 is absorbed and the conversion rate of K1 to K2 is only 5-25%. Research has shown the MK-7 version of K2 is absorbed the best and this form is often used in supplements of vitamin K2. The difference in actions between vitamin K1 and vitamin K2 are as widely contrasting as the dietary sources they are concentrated in.
Whilst the liver utilizes vitamin K1 - found in nature as phylloquinones from dark leafy greens – to initiate a blood-clotting cascade, vitamin K2 is primarily used in other sites of the body to aid in the correct placement of Calcium. Vitamin K2 is present in butter, egg yolk, animal-based foods, fermented foods like Natto and some cheeses.
More on Vitamin K2
This fat-soluble vitamin is a powerhouse nutrient which performs various important functions in the body. Firstly, it helps to maintain bone density by stimulating osteoblasts and thus supporting bone calcification.
Also, vitamin K2 helps keep the blood vessel walls flexible, supports the health of blood vessels and contributes to cardiovascular health. Vitamin K2, specifically the menaquinone-7 (MK-7) variety plays a huge role in calcium metabolism in the body. As such, it’s not only necessary for placement and retention of calcium in bone, but to prevent calcium from building up in the arteries and causing cardiovascular conditions associated with this occurrence.
Research shows K2 may prevent heart disease
The Rotterdam study which spanned 10 years followed 4807 people with increased intake of MK-7 (vitamin K2) - but not K1- containing foods and found they were 52% less likely to develop artery calcification and had a 57% lower risk of dying from heart disease.
In 2008, these findings were confirmed with a population-based study of 16,000 women aged 49 to 70 years, free from cardiovascular disease at baseline. They were followed up for 8 years and the researchers found for each extra 10mcg of vitamin K2 intake- not K1- the risk of heart disease was reduced 9%.
Whilst the two previous studies were only observational studies two randomised controlled trials (the gold standard for research), have also found benefits for K2. One study of 244 healthy post-menopausal women found 180 mcg of vitamin K2 for 3 years improved arterial stiffness and elasticity. The other study was a randomised controlled trial of 243 men and women over 1 year that found intake of MK-7 (or vitamin K2) decreased age related arterial stiffening. Vitamin K2 helps regulate the homeostasis of soft tissue calcification through activation of a vitamin k dependent protein known as matrix Gla protein (MGP).
Boosting your Dietary Intake of Vitamin K2!
Its dietary form is known as menaquinones which are predominantly of bacterial origin and can be found in relatively small quantities in some animal-based and fermented foods. The highest source of dietary vitamin K2 is currently found in a traditional Japanese fermented soybean dish called Natto, containing a whopping 850mcg of vitamin K2 per serving.
But being realistic, unless you have grown up with it, it is unlikely you will acquire the taste for these pungent beans. So where else can we find K2 to boost our dietary intake of this necessary yet elusive vitamin?
1. Grass-fed Butter
Butter is in fact it’s a rich source of brain-loving satiating and natural fats, Vitamins A and D, and of course vitamin K2 - containing 14.5mcg of K2 per 100g serve. As we should be using butter in small quantities, it admittedly isn’t a huge amount, but can contribute to a regular intake of K2 with other sources.
2. Cheese
A terrific source of Vitamin K2! The lactic acid present in cultured cheeses increases the amounts of bacteria-derived K2, so it’s important to choose ‘proper’ cheeses – not pre-packaged sliced for your cheese on toast. Although all cheeses contain a significant amount of the vitamin, Gouda clocks in an average of 50mcg of menaquinone-7 per 100g
3. Grass-fed Meat
Animal’s grazing on lush green grass are able to convert the K1 present into K2, something our gut bacteria are relatively inefficient at doing. So, eating grass-fed meat on a regular basis is a great way to get 4.5mcg per 100g of K2
4. Egg yolk
Ironic that eggs were once demonized as one of the main foods to avoid in a ‘heart healthy’ diet, pasture raised eggs are a rich source of Vitamin K2 with around 32.1mcg per yolk, which of course contributes to heart health via calcium modulation mechanisms.
5. Fermented Foods
Although Natto is by far the richest food source of Vitamin K2, other fermented foods may also contain small amounts, however the measurement of K2 in fermented products such as sauerkraut, kefir, and range of dairy tend to vary widely due to the specificity of the bacteria used in the fermentation process.
Key Takeaways
- Vitamin K2 may reduce arterial stiffness or arterial calcification, further studies are needed to confirm this
- Butter, cultured cheese, egg yolk and fermented foods (including natto) are high vitamin K2 containing foods that can be part of a healthy diet along with the nutrient dense greens containing its sister nutrient K1
- Supplementing with additional vitamin K2 may be required to meet adequate needs when dietary intake is low or digestive function impaired.
Note - remember to consider any medications you may be taking before embarking on any dietary change or new supplement regime in relation to vitamin K and consult your health practitioner if unsure.
