Vitamin K in a nutshell:
Vitamin K is involved in blood clotting, preventing calcification of fatty deposits in the arteries (which can lead to blocked arteries) and in the formation of healthy bones.
Vitamin K is the nutrient we all need but most of us forget. It is essential to healthy blood and bones and to prevent problems caused by high cholesterol.
Phylloquinone; Vitamin K1; Menaquinone; Vitamin K2; Menadione; Vitamin K3.
What Is Vitamin K?
Vitamin K is a chemical compound that exists in the three forms known as phylloquinone, menaquinone, and menadione, or vitamin K1, vitamin K2, and vitamin K3. It is a vital nutrient for human beings, but it is also a vital substance in the plants we eat before they reach our tables.
Every plant makes vitamin K1 to recharge and restore its supply of chlorophyll, the chemical it uses to capture energy from the sun. The greener the plant, the more vitamin K1 it makes. Of the plant parts humans use for food, green leafy vegetables are the best source of vitamin K1, the “greener,” the better.
The reason vitamin K stays in the leaves where it does its work is that it is fat-soluble rather than water-soluble. It does not dissolve in the plant's fluids but it can dissolve in healthy plant fats.
Vitamin K is not just vital for green leafy plants. It is also vital for certain strains of bacteria, including the symbiotic bacteria that live in the lower digestive tract of human beings. These bacteria convert phylloquinone into menaquinone, that is, they transform vitamin K1 into vitamin K2.
One of the many important reasons to maintain the friendly bacteria in your colon is to provide your body with vitamin K2. The bacteria themselves use vitamin K2 to enable them to “breathe” oxygen. Friendly bacteria don't absolutely have to have vitamin K2 to live, but when it is available, they are twice as abundant in the colon.
The human body can't make vitamin K1, but it can change vitamin K1 into vitamin K2. There are slight chemical differences between various forms of vitamin K2, so that the human body produces one kind of isomer of vitamin K2 called MK-4, and bacteria make another kind of vitamin K2 known as MK-7. Don't worry about the nomenclature right now—why it is important will be explained in a moment.
Vitamin K can also be made in the laboratory. The kinds of vitamin K that can be cooked up in the lab are vitamin K3 and vitamin K4. Natural vitamin K is completely non-toxic, but overdoses of artificial vitamins K3 and K4 can cause serious side effects.
What Does Vitamin K Do in the Human Body?
Back in 1929, a Danish scientist named Henrik Dam was working out the function of cholesterol. Vitamin researchers of his time did not use lab rats. They used lab chickens.
The typical scientific protocol of his time was to deprive animals of a nutrient, in this case cholesterol, and to see what happened. Along the way he learned that when his laboratory chickens were deprived of both vitamin K and cholesterol, they developed bleeding disorders. He eventually learned that vitamin K is needed for some kind of coagulation factor that makes it possible for the blood to clot. Since he published his findings in a German-language journal, he called this substance a Koagulationsvitamin, which we now call vitamin K.
Chemically, in both plants and humans, the main task of vitamin K is to receive electrons. That is what vitamin K does to enable the clotting of the blood. The factors that enable the blood to form clots to stop bleeding are “cemented” to the proteins that make a clot with calcium. Calcium has to give up two electrons to “stick” to protein, and vitamin K, after it has been processed by the liver, forms the compound that receives them. We have to have vitamin K to make the clotting factors, but blood clotting also depends on the ability of the liver to use it.
Vitamin K is also essential for healthy bones. You probably know that bones use calcium. Our bones aren't just a collection of minerals like a chunk of cement. They are a living tissue that binds calcium into a net of collagen proteins that makes the bones much stronger. In the bones, vitamin K works with vitamin D to help put calcium in the right places in the bone.
Finally, vitamin K is essential for healthy blood vessels. Most of us have been taught that cholesterol “clogs” arteries like hard water clogs a pipe. This really is not how atherosclerosis happens. Cholesterol that gets stuck in the lining of a blood vessel is not really a problem until it is hardened with calcium. Until this happens—and hardening of the arteries happens due a series of events moderated by the immune system—the blood vessel has an ability to enlarge and contract as needed to keep blood flowing. In the arteries, vitamin K is used to regulate processes that stop calcification and maintain healthy blood flow.
Vitamin K is also needed for the human body to make a protein called Gas6. Exactly what this protein does is not fully understood, but it seems to keep the telomeres (active ends) of DNA from becoming “cemented” into inactive shapes so that cells age more slowly.
What Happens When We Don't Get Enough Vitamin K?
Vitamin K deficiencies result, as you might expect, in increased bleeding. People who don't get enough vitamin K usually exhibit bleeding from membranes. The gums may bleed so that a little or a lot of blood appears on the toothbrush. Black or brown dried blood may be obvious in the stool.
Other consequences of vitamin K deficiency are not as obvious. Bones regenerate themselves over a period of several years. Vitamin K deficiency may contribute to osteoporosis that is not detected until a fall or an injury causes a bone to fracture or break. Hardening of the arteries more often than not (although less often than in the past) is not detected until a heart attack occurs, and in much of the world a first heart attack is usually fatal. As for vitamin K deficiency and aging, the effects of vitamin K deficiency occur all over the body. Accelerated aging may be due to vitamin K deficiency but never detected at all. The European Prospective Study of Cancer and Nutrition also found that vitamin K deficiency increases risk of breast and prostate cancer.
Are You at Risk for Vitamin K Deficiency?
There is a very simple test for risk of vitamin K deficiency. Here it is:
Answer this question yes or no. Do you eat green leafy vegetables at least twice a week.
If the answer is “yes,” you more than likely do not have a vitamin K deficiency. If the answer is “no,” you probably do.
Vitamin K deficiency is most frequent among people who would never, for instance, feast on a big bowl of salad. And who doesn't ever, ever eat salad greens? Newborns and unborns.
Babies are at particular risk of vitamin K deficiency diseases. In some countries, babies are automatically given a shot of vitamin K at birth. In many countries, infants get their vitamin K from breast milk. If mothers don't consume green leafy vegetables, or if mothers have a condition that causes vitamin K deficiency, such as treatment with drugs for epilepsy, the child may show deficiency symptoms very early in life.
Another group of people who are at high risk of vitamin K deficiency is those who suffer an intestinal condition called ileitis. The point in the digestive tract where the human body absorbs vitamin K is the ileum. If the lining of the ileum is injured, vitamin K cannot be absorbed. You can't diagnose ileitis with information from the Internet, but signs you may need to see a doctor about the possibility you have ileitis include diarrhea and blood bowel movements—and sometimes kidney stones are also part of the diagnostic signs.
Taking antibiotics interferes with the production of vitamin K2 by bacteria in the colon. Taking a baby aspirin a day or using aspirin every day for pain interferes with the ability of the body to use an enzyme that recycles vitamin A, as do some medications for mood disorders, migraines, epilepsy, Parkinson's disease, and chronic pain. The newer blood thinners do not interfere with vitamin K, but the older medications like warfarin (Coumadin) and clopidrogel (Plavix) do.
How to Make Sure You Get Enough Vitamin K
Fortunately, it is not hard to make sure you get enough vitamin K. As little as two servings of leafy green vegetables every week may be enough.
Vitamin K is vital to human health, but it is not a vitamin you need to consume every day. Your body uses vitamin K in so many vital processes and in so many locations that even if you did not get any vitamin K at all for up to a month, you probably would not suffer deficiency symptoms (assuming you did not suffer deficiency symptoms at the beginning of the month).
Getting vitamin K into your body, however, is not just a matter of eating the right foods. It is easier for the body to absorb K if it does not pass too fast through the ileum. Eating at least a tiny amount of fat, as little as 5 grams (about 45 calories), slows down the passage of food long enough for the vitamin to be absorbed. Since the body absorbs vitamin K at the same sites it absorbs vitamin A, it's important not to eat vitamin K foods within four hours of taking vitamin A supplements or cod liver oil. And since the body uses the same enzymes to process vitamin K and vitamin E, it is important not to take more than 1200 IU of vitamin E a day if you are vitamin K-deficient.
How much vitamin K do you need? There's never a need for a megadose. Your body could not absorb it even if you took it. Just be sure that over the course of a week you get:
- 840 mcg (micrograms, not milligrams) of K if you are a male 19 or older, or if you are woman who is pregnant or nursing,
- 630 mcg if you are a female 19 or older,
- 500 mcg for teens of both sexes,
- 450 mcg for “tweens” (ages 9 to 13) of both sexes,
- 400 mcg for children aged 4 to 8,
- 200 mcg for children aged 1 to 3, and
- 20 mcg for infants.
Where to get Vitamin K
You don't need to measure your vitamin K consumption precisely if you make a point of getting your weekly servings of high-K foods.
Which foods provide the most vitamin K? In each 3-1/2 oz (100 gram) serving there are:
- 1140 mcg in raw amaranth leaves,
- 882 mcg in cooked kale,
- 832 mcg in raw Swiss chard (silverbeet),
- 778 mcg in raw dandelion greens,
- 551 mcg in cooked dandelion greens,
- 542 mcg in cooked spinach,
- 519 mcg in cooked collard greens,
- 483 mcg in raw spinach,
- 462 mcg in canned spinach,
- 327 mcg in cooked Swiss chard (silverbeet),
- 177 mcg in raw Brussels sprouts,
- 174 mcg in green leaf lettuce,
- 142 mcg in cooked broccoli,
- 141 mcg in cooked Brussels sprouts,
- 116 mcg in cooked Asian cabbage,
- 109 mcg in cooked white (common) cabbage,
- 103 mcg in romaine lettuce,
- 102 mcg in cos lettuce,
- 88 mcg in frozen chopped broccoli,
- 80 mcg in cooked asparagus,
- 78 mcg in sweet cucumber pickles,
- 77 mcg in raw cabbage and
and about 40 mcg in the fermented whole soybean food known as natto. There are many health benefits from eating natto (not to be confused with nattokinase), but getting lots of vitamin K is not among them.
Kale and Swiss chard (silverbeet) are the two best foods for getting your vitamin K. A single serving of either vegetable once a week, either raw with a little olive oil in a salad or steamed and served with a tiny amount of oil or added to a smoothie, will provide anyone with enough vitamin K. You will need to eat proportionally more of the vegetables lower on the list. There is also some vitamin K2 in certain kinds of cheese and fermented meat (for example, salami) and fish, but not enough to count in your diet.
You may be surprised that cooked vegetables can have more vitamin K than raw vegetables (see spinach above). That's because cooking doesn't remove vitamin K, but removes water from the vegetable.
What about vitamin K supplements? Because real food contains a wide range of nutrients, supplemental vitamin K is always a second choice. But as little as 1 mg of vitamin K1 (phylloquinone) twice a week (taken twice a week to ensure that it is absorbed) can provide all your vitamin K needs. Consult your physician if you are taking warfarin (Coumadin) or clopidrogel (Plavix) or you have been instructed to limit your consumption of vitamin K.