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Researched Based: This article is based on research. Number’s in Brackets are links to research papers and Scientific articles from well-established and authoritative websites (all links open in a new window).

In this article, we are exploring Vitamin K – a group of compounds such a Vitamin K1 and Vitamin K2.

What is Vitamin K

Vitamin K is a nutrient essential for life and health. It is involved in many important body functions, such as preventing blood clotting and maintaining healthy bones.

It is one of the most basic fat-soluble vitamins, i.e. it requires the presence of fat in order to be absorbed by the body.

The term vitamin K refers to a group of molecules with a similar chemical structure and action. In its natural form it is found in a wide variety of foods and in food supplements.

Vitamin K is classified into two main forms, vitamin K1 (phylloquinone) and vitamin K2 (menaquinone).

Vitamin K1 is mainly found in plant sources, such as green leafy vegetables (spinach, broccoli, lettuce, etc.), vegetable oils and certain fruits (blueberries, figs, etc.).

Related: Vitamin C: Sources, Health Benefits, Deficiency, Side effects, RDA

In contrast, vitamin K2 is mainly of microbial origin. Much of the daily vitamin K requirements in humans are produced by gut bacteria in the form of K2.

In nature, menaquinone is present in moderate amounts in animal products such as meat, milk, soy or eggs, and in fermented products such as traditional Natto food.

Although both types of vitamin K are equally beneficial to health, vitamin K2 (menaquinone) appears to have greater potency.

Unlike the other fat-soluble vitamins (A, D, E), vitamin K circulates in small amounts in the blood, as it is metabolized very quickly and then excreted. This means that when we ingest vitamin K1, only 30% to 40% is retained in our body, with the remaining 60 to 70% being eliminated through urine and stool.

Vitamin A Daily Requirements

Vitamin K requirements by age group are shown in the table below:

Birth – 6 months2,0 μg2,0 μg
7 – 12 months2,5 μg2,5 μg
1 – 3 years30 μg30 μg
4 – 8 years55 μg55 μg
9 – 13 years60 μg60 μg
14 – 18 years75 μg75 μg75 μg75 μg
19+ years120 μg90 μg90 μg90 μg

Vitamin A Foods

Foods that are considered good sources of vitamin K (in the form of vitamin K1) are vegetables, especially green leafy vegetables, while we can also get it from certain vegetable oils (e.g. soybean oil, rapeseed oil), fruits (kiwi, dried figs, avocados, blackberries, grapes, pear, mango, papaya) and nuts.

Meat, dairy products and eggs contain vitamin K1 at low levels, but vitamin K2 is found at higher levels in these foods. Also, fermented cheeses contain vitamin K2.

In more detail, the table below shows the vitamin K content of certain foods (mainly vitamin K1, unless the vitamin K2 content of the food is indicated in a note):

FoodsAmountVitamin K (mcg)
Kale, cooked125 mL (½ cup) 561
Kale, raw, chopped250 mL (1 cup)499
Spinach, cooked125 mL (½ cup) 469
Dandelion greens, raw, chopped250 mL (1 cup)452
Mustard greens, cooked, chopped125 mL (½ cup) 438
Collards, cooked, chopped125 mL (½ cup) 408
Beet greens, cooked125 mL (½ cup) 368
Swiss chard, raw250 mL (1 cup)316
Dandelion greens, cooked125 mL (½ cup) 306
Swiss chard, cooked125 mL (½ cup) 303
Turnip greens, cooked125 mL (½ cup) 280
Parsley, raw60 mL (¼ cup) 260
Collards, raw, chopped250 mL (1 cup)166
Beet greens, raw250 mL (1 cup)161
Lettuce, spring mix (mesclun), raw250 mL (1 cup)154
Spinach, raw250 mL (1 cup)153
Endive and escarole, raw, chopped250 mL (1 cup)122
Brussel sprouts, cooked4 sprouts118
Broccoli, cooked125 mL (½ cup) 116
Radicchio, raw, shredded250 mL (1 cup)108
Lettuce, green leaf, raw, shredded250 mL (1 cup)103
Broccoli, raw, chopped250 mL (1 cup)94
Watercress, raw, chopped250 mL (1 cup)90
Bean sprouts, soybean, raw125 mL (½ cup) 70
Lettuce, romaine, raw, shredded250 mL (1 cup)61
Cabbage, raw, shredded250 mL (1 cup)56
Green or scallion onion, raw, chopped60 mL (¼ cup) 55
Asparagus, cooked6 spears46
Kiwifruit1 medium fruit28
Rhubarb, cooked125 mL (½ cup) 27
Blueberry, frozen125 mL (½ cup) 22
Avocado½ fruit 21
Pork liver75 g (2 ½ oz) 66
Sausage (pork, veal)75 g (2 ½ oz) 53
Tuna, light, canned with oil75 g (2 ½ oz) 33
Soybeans, cooked175 mL (¾ cup) 24
Matcha green tea powder2 g of tea powder60

Vitamin A Health Benefits

  • Protein Synthesis: Vitamin K is essential for the synthesis of proteins involved in blood clotting and bone metabolism, as well as other physiological functions.

One of the best known proteins that depends on the action of vitamin K and is directly involved in blood clotting is prothrombin (clotting factor II).

Osteocalcin is another vitamin K-dependent protein found in bone and regulates calcium deposition in bone, and it appears that the presence of vitamin K is essential for its synthesis.

In addition, vitamin K is absorbed from the small intestine, participates in lipid metabolism and is transported to the liver, where it is repackaged into very low-density lipoproteins (VLDL).

  • Coagulation of blood: Vitamin K helps in blood clotting, stopping bleeding, reduces bruising as well as faster wound healing. [1] The process of blood clotting is a highly complex process.

Many of the proteins involved in the formation of clotting need vitamin K for their proper action. Without the required amount of vitamin K there is an increased risk of bleeding.

  • Cardiovascular health: One of the major causes of heart attack is the deposition of calcium in the arteries [2]. Calcification of the arteries makes them harder, with reduced elasticity and reduces their width, making them narrower.

Taking vitamin K prevents calcium deposition in the vessels and tissues, it is suggested that it indirectly participates in cardiovascular protection [x]. However, larger and better designed studies are needed to highlight the role of vitamin K in preventing cardiovascular disease.

  • Osteoporosis: Osteocalcin is a vitamin K-dependent hormone responsible for bone health, specifically for the deposition and elimination of calcium from bone. Specifically, vitamin K helps calcium circulating in the blood to be stored in the bones [3].

According to studies, people who consume large amounts of vitamin K through food or supplements have stronger bones and are less likely to suffer a bone fracture in their lifetime even if the individuals already had osteoporosis [4].

The action of vitamin K is enhanced by the action of vitamin D, which is why it is recommended to be taken together for better absorption of calcium by the bones.

  • Improving brain health and inflammation: It is now proven that chronic conditions such as Alzheimer’s disease, cancer, Parkinson’s disease as well as heart failure are inflammatory conditions. [5]

In recent years, more and more studies have shown that vitamin K has anti-inflammatory properties, protecting brain cells from oxidative stress and the harmful effects of free radicals. [6]

Hand holding Kale - one of the top Vitamin K sources
Kale is one of the top foods that contain Vitamin K

Vitamin K Deficiency

Vitamin K deficiency is not common and can only occur in people who have malabsorption problems or liver disease. In healthy people, whose diet is varied, it is almost impossible to achieve a low intake of vitamin K so that blood clotting is affected.

However, in case of vitamin K deficiency, the activity of prothrombin in blood is significantly reduced, resulting in bleeding. Similarly, deficiency of this vitamin may lead to the development of osteoporosis. The groups at risk of vitamin K deficiency are:

  • Newborns and infants who are not given vitamin K supplementation in the first weeks (2nd – 12th) of life (due to low vitamin K1 transfer to the placenta, low levels of clotting factors and low vitamin K content in breast milk.
  • People with malabsorption disorders (e.g. cystic fibrosis, celiac disease, ulcerative colitis, short bowel syndrome);
  • Patients who have undergone bariatric surgery;
  • People taking medications that interfere with vitamin K metabolism;

*Vitamin K Toxicity effects are unlikely to occur due to increased vitamin K intake [7].

Related: Best Vitamin B Complex Supplement & Everything You Need To Know In Between

Vitamin A Pregnancy

Vitamin K is particularly important during pregnancy, especially in cases of premature birth. All premature babies show symptoms of haemorrhagic syndrome, more or less severe, related to the availability of vitamin K.

In particular, premature babies are likely to have a marked vitamin K deficiency, their intestinal tract may not be inhabited by those micro-organisms that synthesize vitamin K and the vitamin K stores in their liver may be inefficient.

Consequently, vitamin K supplementation may contribute significantly to the prophylaxis of premature infants from complications due to haemorrhage.

Vitamin K, which is naturally present in human breast milk, has been shown to be inadequate relative to that required by infants less than 6 months of age. Supplementation during breastfeeding improves the vitamin K content of breast milk and reduces the potential for neonatal haemorrhage.

Vitamin K Supplements

Below are some of the best Vitamin K supplements that you can buy online or via your local pharmacy.

Final Take

Vitamin K is important for protein synthesis, strong bones, brain and blood clotting. If you eat your vegetables, you probably don’t need a supplement.

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