Vitamin K commonly refers to a group of five structurally similar fat-soluble vitamins. Only two of the five types of vitamin K occur naturally.
Phylloquinone, also known as vitamin K1, is found in plants and performs the traditional functions of vitamin K. Phylloquinone is an active factor in photosynthesis and is found in high amounts in leafy green vegetables like kale and Swiss chard.
Vitamin K1 can be converted to its storage form, Vitamin K2, by bacteria in the large intestine. Vitamins K3-5 are synthetic and can be purchased as supplements.
Vitamin K plays a major role in blood clotting, bone metabolism and the regulation of blood calcium levels. It is absorbed in the small intestine and stored in fatty tissue and the liver. Vitamin K is utilized by the liver in the production of prothrombin (clotting factor).
However, vitamin K is also a nutrient of concern for many people as it can alter the effects of several common medications such as warfarin.
Vitamin K deficiency is rare and typically only occurs in people with malabsorptive conditions or after long-term treatment with antibiotics. Symptoms of deficiency include prolonged clotting time, hemorrhage and excessive bleeding.
This MNT Knowledge Center feature provides an in-depth look at the recommended intake of vitamin K and a breakdown of its possible health benefits, how to incorporate more vitamin K into your diet and any potential health risks of consuming vitamin K.
Contents of this article:
Recommended vitamin K intake
The recommended adequate intake for vitamin K depends on age and gender:
|0-6 months||2 mcg/day|
|7-12 months||2.5 mcg/day|
|1-3 years||30 mcg/day|
|4-8 years||55 mcg/day|
|9-13 years||60 mcg/day|
|14-18 years||75 mcg/day|
|19+ years, females||90 mcg/day|
|19+ years, males||120 mcg/day|
Vitamin K supplements are available but it is best to obtain any vitamin or mineral through food first. It is not the individual vitamin or mineral alone that makes certain foods an important part of our diet but the synergy of nutrients working together.
Experts have proven time and again that isolating certain nutrients in supplement form will not provide the same health benefits as consuming that same nutrient from a whole food. Focus on obtaining your daily vitamin K requirement from food and use supplements only when necessary.
Possible health benefits of consuming vitamin K
Vitamin K may help individuals maintain low blood pressure by preventing several minerals from accumulating in the arteries.
There is a correlation between low intake of vitamin K and osteoporosis.2 Although several studies have suggested that vitamin K supports the maintenance of strong bones, improves bone density and decreases the risk of fractures, others have shown no improvement in bone density associated with vitamin K.2
Increased blood levels of vitamin K have been linked with improved episodic memory in older adults.3 In one study, healthy individuals over the age of 70 with the highest blood levels of vitamin K-1 had the highest verbal episodic memory performance.
Vitamin K may help keep lower blood pressure by eliminating the build-up of several minerals in the arteries (mineralization), allowing the heart to freely push blood through the body. Mineralization naturally occurs with age and is a major risk factor for heart disease. Adequate intake of vitamin K has also been shown to lower the risk of stroke.4
How to incorporate more vitamin K into your diet
Leafy greens and cruciferous vegetables are two of the best sources of vitamin K:
- Kale, cooked, ½ cup: 630 mcg
- Collard greens, cooked, ½ cup: 520 mcg
- Spinach, cooked, ½ cup: 510 mcg
- Turnip greens, cooked, ½ cup: 425 mcg
- Swiss chard, cooked, ½ cup: 287 mcg
- Brussels sprouts, cooked, ½ cup: 110 mcg
- Cauliflower, raw, ½ cup: 96 mcg
- Parsley, 10 sprigs: 90 mcg
- Broccoli, raw, ½ cup: 58 mcg
- Asparagus, cooked, ½ cup: 75 mcg
- Lettuce, green leaf, raw, ½ cup: 50 mcg.
Cooked kale is one of the best sources of vitamin K, with half a cup containing 630 mcg.
Try these healthy recipes developed by a registered dietitian to increase your vitamin K intake:Baked halibut with garlicky kale & toasted cashews
Powered-up spinach lasagna
Roasted Brussels sprouts with toasted pecans & avocado
The absorption of vitamin K is enhanced by dietary fat.
Potential health risks of consuming vitamin K
No tolerable upper limit has currently been determined for vitamin K. Toxicity is rare and unlikely to occur by eating foods containing vitamin K. However, toxicity is possible when taking any supplement.
Vitamin K can alter the effect of a number of different medications, including the widely-used blood-thinning medication warfarin.
Vitamin K can interact with several common medications, including blood-thinners, anticonvulsants, antibiotics, cholesterol-lowering and weight-loss drugs.
Blood thinners such as warfarin are used to prevent harmful blood clots that may block blood flow to the brain or heart. Essentially, they decrease or delay vitamin K's clotting ability. A sudden increase or decrease in vitamin K intake can interfere with the effects of these drugs. Aim to keep your intake of vitamin K rich foods consistent from day to day.
For pregnant or breastfeeding women, taking anticonvulsants (phenytoin, dilantin) increases the risk of vitamin K deficiency in their newborns.
Cholesterol-lowering medications interfere with fat absorption. Because vitamin K absorption is dependent on dietary fat, taking this medication may increase the risk of deficiency.
Speak to your physician if you are on any of these medications and have further questions about your vitamin K intake.
And Mary Curnette, nutrition intern.