Vitamins are essential micronutrients that perform many functions within the body. Most significantly, they regulate the thousands of chemical reactions that sustain life – from efficient energy use to the maintenance of healthy cells, tissues, and organs.
Each of the 13 vitamins exert unique actions, but often do so in tandem. We know that vitamin A is important to healthy skin and eyes. Vitamin C helps repair tissue and boosts the immune system. The eight B complex vitamins maintain the metabolism. Vitamin D increases the absorption of calcium and other minerals. Vitamin E affects gene expression while promoting healthy skin and muscles. And, of course, vitamins A, C, and E are antioxidants that limit damaging free radicals.
The wallflower of the group, vitamin K seems to get little attention but is just as important to our health. Read on to learn more about what vitamin K is, what it does in our bodies, and its best food sources.
What is Vitamin K?
First discovered in 1929, vitamin K refers to a group of fat-soluble compounds all organisms require for healthy blood, bones, and tissues.
It is available in two forms: vitamin K1 (phylloquinone), which is present in leafy vegetables and vitamin K2 (menaquinones), found in animal livers and fermented foods.
When we consume foods rich in it, vitamin K does the vital job of synthesizing specific proteins in the body. Once ingested, vitamin K metabolizes rapidly and becomes depleted. The body is able to recycle and reuse a small amount of vitamin K many times over. But unlike other fat-soluble vitamins, very little of vitamin K is stored in the fat or blood. For this reason, it is important to include a serving or two of vitamin K rich foods in each meal to replenish your stores.
6 Health Benefits of Vitamin K
1. Vitamin K Promotes Healthy Blood Clotting
Vitamin K is most well known as the “coagulation vitamin” due to the key role it plays in hemostasis. Its discovery was accidental; scientists were examining the effects of a fat-free diet on chickens when they noticed that the animals continued bleeding from tag sites. In fact, the name vitamin K is derived from the German Koagulationsvitamin, the term first used to describe it.
After a physical injury, the first step towards wound healing is coagulation – where the blood turns from a liquid into a gel. For this change to occur, calcium ions need to bind to certain proteins in the blood. Our bodies do not have an innate way to do this, and so vitamin K must be present to complete the series of steps, known as the coagulation cascade. Without vitamin K, blood would not clot and we would bleed uncontrollably.
People who are at a higher risk of harmful blood clots and take blood thinning medications, such as warfarin, should be consistent with their vitamin K intake. A sudden increase or decrease of vitamin K in the diet can impact the effect of these types of drugs. Speak with your doctor to determine the correct dose of warfarin to best accommodate your normal diet.
2. Vitamin K Keeps Bones Strong
In a 10-year observational study involving over 72,000 women between the ages of 38 and 63, researchers found that there was a lower risk of hip fractures when high to moderate amounts of vitamin K was regularly consumed in the diet. Women who ate lettuce one or more times per day, for example, had a 45% lower risk of hip fractures than those who ate lettuce once or fewer times per week. And as with calcium, vitamin K is better absorbed by the body when taken along with vitamin D.
In another large prospective study that followed 2,591 volunteers for four years, women with the lowest vitamin K intakes had significantly lower bone mineral density in the neck and spine.
3. Vitamin K is Good for the Heart
Cardiovascular disease is the umbrella term for many ailments of the circulatory system, including stroke, heart failure, angina, heart attack, arrhythmia, and aneurysm. A common precursor between all cardiovascular diseases is atherosclerosis, the narrowing of the arteries due to plaque. Over time the plaque hardens and calcifies, increasing the risk of rupture followed by a cardiovascular event.
There is a link between calcification of the arteries and low bone mass, dubbed the “calcification paradox”, that is most common in postmenopausal women. Having a low vitamin K status has been shown to increase one’s risk of developing these conditions. But vitamin K appears to play a role in both preventing arteries from calcifying while also promoting bone mineralization.
Other research on vitamin K and cardiovascular disease as a whole has been promising. In a 2013 cohort study that tracked 3,401 participants for 13 years, people who consumed the recommended daily value of vitamin K had a lower risk of death from cardiovascular disease and all-cause mortality. In another paper, researchers discovered that high vitamin K2 intake was associated with a significant reduction of instances of coronary heart disease.
4. Vitamin K May Lower Cancer Risk
While human trials are needed, the results from a large observational study has shed some more light on the subject. Published in The American Journal for Clinical Nutrition, the investigation involved more than 24,000 participants between the ages of 35 and 64 who were cancer-free at enrollment. After a 10 year follow up, there were 1,755 diagnoses of cancer, and 458 of these cases were fatal. Looking at the intakes of vitamin K, researchers found that there was an association between higher consumption of vitamin K2 and lower rates of cancer, including fatal cancer.
5. Vitamin K & Longevity
Because vitamin K has been linked to reduced cardiovascular disease and cancer risk (the top two leading causes of death in the US), scientist have wondered how this vitamin might affect one’s lifespan in general.
According to a 2014 paper published in The Journal of Nutrition, consuming plenty of vitamin K in the diet does indeed reduce the risk of mortality from all causes. With a study population of 7,216 individuals who were at a higher risk of cardiovascular disease, researchers followed up with the participants after five years and found that higher intakes of both vitamin K1 and K2 was associated with a significantly reduced risk of cancer, cardiovascular disease, and death from other causes compared to those with who consumed less vitamin K foods.
6. Vitamin K is Neuroprotective
Although much of the research on vitamin K has focused on blood and bone health, it is also essential for the synthesis of sphingolipids – a type of fat found in high concentrations in the brain. Sphingolipids are major components of brain cell membranes and are important to their structure and cell signalling. They also depend on vitamin K proteins to function properly.
Vitamin K’s relationship with sphingolipids may explain why it appears to play a beneficial role in brain health and cognition as we age. A 2013 study of older adults between 70 to 85 years old found that higher levels of vitamin K in the body were associated with greater ability to remember past personal experiences. Similarly, another study discovered that people who consumed less vitamin K had more severe “subjective memory complaints” – or how the patient feels about their own ability to remember things. After supplementing with vitamin K, these same individuals reported that their memory had improved.
14 Best Food Sources of Vitamin K1 & K2
The recommended daily intake of vitamin K for people over the age of 19 is 120 micrograms for men and 90 micrograms for women. Since there are no upper limits, you needn’t worry about having too much vitamin K in your diet.
And as you will see, vitamin K1 is abundant in the plant kingdom…
Kale – Per cup, 684% of the DV.
Parsley – Per ounce, 574% of the DV.
Dandelion Greens – Per cup, 535% of the DV.
Swiss Chard – Per cup, 374% of the DV.
Mustard Greens – Per cup, 348% of the DV.
Spring Onions – Per cup, 259% of the DV.
Collard Greens – Per cup, 230% of the DV.
Brussels Sprouts – Per cup, 195% of the DV.
Beet Greens – Per cup 190% of the DV.
Spinach – Per cup, 181% of the DV.
Turnip Greens – Per cup, 173% of the DV.
Broccoli – Per cup, 116% of the DV.
Leaf Chicory – Per cup, 108% of the DV.
Cabbage – Per cup, 85% of the DV.
Sources of vitamin K2, on the other hand, can be readily found in fermented foods such as the Japanese dish nattō (per cup, 51% of the DV). Other sources include hard and soft cheeses, egg yolks, and chicken liver.
Eating plenty of vegetables rich in vitamin K1 also means we are obtaining vitamin K2, since our bodies are able to convert phylloquinone to menaquinones via bacteria in the gut.