Vitamins are substances that your body needs to grow and develop normally. Vitamin K helps your body by making proteins for healthy bones and tissues. It also makes proteins for blood clotting. If you don't have enough vitamin K, you may bleed too much.

Newborns have very little vitamin K. They usually get a shot of vitamin K soon after they are born.

If you take blood thinners, you need to be careful about how much vitamin K you get. You also need to be careful about taking vitamin E supplements. Vitamin E can interfere with how vitamin K works in your body. Ask your health care provider for recommendations about these vitamins.

There are different types of vitamin K. Most people get vitamin K from plants such as green vegetables, and dark berries. Bacteria in your intestines also produce small amounts of another type of vitamin K.

Vitamin K is a nutrient that the body needs to stay healthy. It’s important for blood clotting and healthy bones and also has other functions in the body. If you are taking a blood thinner such as warfarin (Coumadin®), it's very important to get about the same amount of vitamin K each day.

Although the Vitamin K shot is safe and, as recommended by the American Academy of Pediatrics, has been routinely given to newborns at birth since 1961, some parents refuse the shot due to myths and misperceptions about its safety. This puts babies at risk for dangerous bleeding which can lead to brain damage and even death.

Purpose of Vitamin K

Vitamin K refers to a group of structurally similar fat- soluble molecules that are primarily involved in the synthetic pathways of a number of clotting factors. Vitamin K is also involved in bone metabolism.

Sources of Vitamin K

Adults get vitamin K from food — mainly leafy green vegetables — and from bacterial synthesis in the gut. Babies have very little vitamin K in their bodies at birth because only small amounts of the vitamin pass through the placenta. Also, the bacteria that produce the vitamin in the newborn’s intestines are not yet present. Breast milk contains only low levels of vitamin K, and it may take weeks to months for the infant’s ‘sterile’ gut to become established and functional. Infants are therefore predisposed to having low vitamin K levels, resulting in low levels of vitamin K-dependent clotting factors, and an increased risk for bleeding, termed vitamin K deficiency bleeding.

What is vitamin K deficiency bleeding (VKDB)?

Infants who do not receive the vitamin K shot are at risk for developing VKDB.

VKDB can be classified according to the time of presentation after birth into early (0–24 hours), classical (1–7 days) and late (2–12 weeks) VKDB. Early VKDB is severe, and is mainly found in infants whose mothers used certain medications during pregnancy that interfere with vitamin K metabolism, such as certain anticonvulsants or isoniazid. Classical VKDB is typically characterized by bruising or bleeding from the umbilicus. Late VKDB is the most concerning type — this bleeding occurs up to 6 months of age in previously healthy infants, and between 30–60% of late VKDB presents as an intracranial bleed. This life-threatening complication tends to occur in exclusively breastfed infants who have received no or inadequate vitamin K prophylaxis; warning bleeds before an initial severe event are rare.

Infants who do not get the vitamin K shot at birth are at 81 times greater risk for developing VKDB than infants who do get the shot. VKDB is effectively prevented by the vitamin K shot — incidence of late VKDB, the most concerning type, falls to less than 1/100,000 infants when vitamin K is given at birth.

What are the warning signs of VKDB?

In the majority of cases of VKDB, there are NO WARNING SIGNS at all before a life-threatening bleed occurs. Infants who do not get vitamin K at birth might develop any of these signs of VKDB:

• Bulging fontanelles
• Diffused bruising and ecchymosis
• Feeding intolerance, irritabilities
• Epistaxis
• Jaundice and pallor

The amount of vitamin K you need depends on your age and sex. Average daily recommended amounts are listed below in micrograms (mcg).

Vitamin K is found naturally in many foods. You can get recommended amounts of vitamin K by eating a variety of foods, including the following:

• Green leafy vegetables, such as spinach, kale, broccoli, and lettuce
• Vegetable oils
• Some fruits, such as blueberries and figs
• Meat, cheese, eggs, and soybeans

Vitamin K is found in multivitamin/multimineral supplements. Vitamin K is also available in supplements of vitamin K alone or of vitamin K with a few other nutrients such as calcium, magnesium, and/or vitamin D. Common forms of vitamin K in dietary supplements are phylloquinone and phytonadione (also called vitamin K1), menaquinone-4, and menaquinone-7 (also called vitamin K2).

Vitamin K deficiency is very rare. Most people in the United States get enough vitamin K from the foods they eat. Also, bacteria in the colon make some vitamin K that the body can absorb. However, certain groups of people may have trouble getting enough vitamin K:

• Newborns who don’t receive an injection of vitamin K at birth
• People with conditions (such as cystic fibrosis, celiac disease, ulcerative colitis, and short bowel syndrome) that decrease the amount of vitamin K their body absorbs
• People who have had bariatric (weight loss) surgery

Severe vitamin K deficiency can cause bruising and bleeding problems because the blood will take longer to clot. Vitamin K deficiency might reduce bone strength and increase the risk of getting osteoporosis because the body needs vitamin K for healthy bones.

Scientists are studying vitamin K to understand how it affects our health. Here are some examples of what this research has shown.

Osteoporosis

Vitamin K is important for healthy bones. Some research shows that people who eat more vitamin K-rich foods have stronger bones and are less likely to break a hip than those who eat less of these foods. A few studies have found that taking vitamin K supplements improves bone strength and the chances of breaking a bone, but other studies have not. More research is needed to better understand if vitamin K supplements can help improve bone health and reduce osteoporosis risk.

Coronary heart disease

Scientists are studying whether low blood levels of vitamin K increase the risk of coronary heart disease, perhaps by making blood vessels that feed the heart stiffer and narrower. More research is needed to understand whether vitamin K supplements might help prevent heart disease.

Vitamin K has not been shown to cause any harm. However, it can interact with some medications, particularly warfarin (Coumadin®)—see the information below.

Yes, some medications may interact with vitamin K. Here are a few examples:

Warfarin (Coumadin®)

Vitamin K can have a serious interaction with the blood thinner warfarin (Coumadin®). If you take warfarin, make sure that the amount of vitamin K you consume from food and supplements is about the same every day. A sudden change in the amount of vitamin K you get can cause dangerous bleeding (if you consume less) or blood clots (if you consume more).

Antibiotics

Antibiotics can destroy the good bacteria in your gut. Some of these bacteria make vitamin K. Using antibiotics for more than a few weeks may reduce the amount of vitamin K made in your gut and therefore, the amount available for your body to use.

Bile acid sequestrants

Some people take bile acid sequestrants (such as cholestyramine [Questran®] and colestipol [Colestid®]) to lower blood cholesterol levels. These medications can reduce the amount of vitamin K your body absorbs, especially if you take them for many years.

Orlistat

Orlistat (Alli® and Xenical®) is a weight-loss drug. It reduces the amount of fat your body absorbs and can decrease the absorption of vitamin K.

Tell your doctor, pharmacist, and other healthcare providers about any dietary supplements and prescription or over-the-counter medicines you take. They can tell you if the dietary supplements might interact with your medicines or if the medicines might interfere with how your body absorbs, uses, or breaks down nutrients such as vitamin K.