Vitamin K: Health Benefits, Daily Intake, and Sources

Vitamin K is gaining attention because it has a much greater effect on our health than previously thought. It isn’t a single substance, but a family of nutrients that plays a critical role in preventing disease, including osteoporosis and hardening of arteries that leads to heart attacks and strokes.

Traditionally, vitamin K has been viewed as essential for healthy blood clotting—we could bleed to death from a minor cut without it. In this sense, deficiency has not been viewed as a problem for healthy people, but this holds true for only one form of the vitamin: K.

Vitamin K is another story. In nature, it exists in 10 subtypes whose names—MK-4 through MK-13—designate different molecular structures within the K family. All of their functions are not fully understood yet, and there is no established daily requirement for vitamin K, but the need is clear.

Did You Know?

Antibiotics and cholesterol-lowering drugs interfere with vitamin K and can deplete levels.

Why Vitamin K Is Essential

Research has shown that vitamin K has a pivotal effect on how our bodies utilize calcium. Higher levels of K correlate with calcium being deposited in bones, where it helps to prevent osteoporosis, while low levels correlate with harmful calcium deposits in arteries. In Japan, vitamin K is an approved treatment for osteoporosis. It’s been shown to stop decline in bone mineral density and, in some cases, to reverse it. Here are some research highlights:

• In the Netherlands, the effects of vitamins K and K were examined among 4,807 healthy men and women, who were aged 55 or older at the outset. Their diets and health were monitored for up to 10 years. Dietitians calculated the amounts of vitamins K and K in participants’ diets and found that those who consumed the most K developed the least coronary artery disease and were least likely to die. There was no similar correlation with vitamin K.
• A study of 244 postmenopausal women compared the effects of taking a placebo or 180 mcg of the MK-7 form of vitamin K (MenaQ7, a patented form), daily for 3 years. Bone scans showed that the MK-7 supplement significantly reduced age-related bone loss and increased the strength of bones.
• Another study looked at vitamin K in the diets of 16,057 women who were between the ages of 49 and 70 and had no heart disease. Researchers monitored them for 6–8 years and found that those who consumed the most vitamin K developed the least heart disease; vitamin K, however, did not affect the heart.

Low levels of vitamin K also correlate with higher incidence of diabetes. In addition, emerging research is finding a link between adequate K and cancer prevention, proper immune function, and healthy liver, kidney, and neurological function.

Food Sources of Vitamin K

Vitamin K is found in leafy green vegetables, and it’s estimated that most people get enough K from food. But our levels of vitamin K quite likely fall short.

The richest source of K is natto, a fermented soy food that isn’t a usual part of a Western diet. Other sources include animal foods, especially liver and dark meat with skin from chicken and duck, egg yolks, and full-fat cheeses. Foods from grass-fed animals, who convert the vitamin K in grass into vitamin K, contain more K than the same foods from grain-fed animals. A Western diet may not provide enough K, but supplements can bridge the gap.

Two Types of Vitamin K 

1. Vitamin K (phylloquinone): 

Enables healthy blood clotting. Daily recommended amounts are 90 mcg for women and 120 mcg for men, which are easy to get from leafy greens or multivitamins.

2. Vitamin K (menaquinone): 

Essential for calcium to be used in bones rather than arteries, where calcium deposits lead to heart disease. There is no set recommended daily amount, but in a Western diet, levels may well fall short of optimum.

The MK-7 subtype of vitamin K is measured in micrograms (mcg), whereas the MK-4 subtype is typically measured in milligrams (mg). Studies have used 180 mcg of MK-7 or 15–45 mg of MK-4. Products described as “full spectrum” or as a “complex” contain multiple subtypes.

There is no recommended upper limit, as the vitamin is not considered to be toxic. Vitamin K is fat-soluble and is absorbed more effectively when taken with fatty food.

Caution: Vitamin K supplements (K and K) are not recommended for anyone taking blood-thinning medications. These typically work by blocking vitamin K, and taking the vitamin can reduce effectiveness of the drugs.

Try our Dark Leafy Pesto recipe

Vitamin K Supplements