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What you should know about a vitamin K deficiency

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If your nose is always bleeding or you keep getting bruises, you may be low on this essential nutrient. Here’s how vitamin K works and how to tell if you’re getting enough.
Written by Hallie Levine
Updated on February 25, 2022

When you think about essential vitamins, your mind probably goes straight to C or D. You might not think about vitamin K. But you should.

“Vitamin K is needed for blood clotting, and there’s also evidence that it may support bone health and help lower blood pressure,” says Paula Doebrich. She’s a registered dietitian nutritionist and the owner of Happea Nutrition in New York City.

In other words, vitamin K is vital. A 2020 study from the American Journal of Clinical Nutrition showed how important vitamin K really is. It found that older adults with low levels of it were 19% more likely to die than those with adequate levels.

Keep reading to learn about this essential vitamin. (Medication can be essential, too, and that’s why you don’t want to overpay at the pharmacy. Download our free mobile app to search for prescription coupons.)

What vitamin K does

Like all vitamins, vitamin K plays a complex role in the body. But its most significant job is to help build proteins that keep you strong. Here are the primary ways it affects you:

It helps your blood clot

Vitamin K helps your body make 4 of the 13 proteins needed for blood clotting, according to the Harvard T.H. Chan School of Public Health. That means that if you cut or injure yourself, vitamin K can keep you from losing too much blood.

It helps you build bone

“Vitamin K activates certain proteins in your body that are involved in the mineralization of bones,” says Rachel Dyckman, a registered dietitian nutritionist in New York City.

That makes sense when you consider a 2020 study from the medical journal Bone. It found that post-menopausal women with low vitamin K levels were about 40% more likely to fracture a hip than women with higher levels.

It may protect you from heart disease

Some of the proteins that vitamin K helps create can keep your arteries from becoming stiff, says Dyckman. That’s important given that heart disease is still the top cause of death in the United States, according to the Centers for Disease Control and Prevention.

According to a study published in the Journal of the American Heart Association, those who got the most vitamin K from their diet had about a 15% to 20% lower chance of being hospitalized with cardiovascular disease, compared with those who consumed low levels of vitamin K.

How to tell if you’re deficient in vitamin K

Eating too little vitamin K is associated with bone diseases such as osteoporosis. But the most common sign of vitamin K deficiency is excessive bleeding, according to a Merck medical reference manual. And that can show up in several ways:

  • Easy bruising
  • Frequent nosebleeds
  • Vomiting up blood (from stomach bleeding)
  • Black stool (from blood in the bowels)

The good news is that vitamin K deficiency in adults is rare. “There are bacteria in our intestines that synthesize vitamin K for us, and we have a mechanism for recycling vitamin K in the body,” says Kristian Morey. She’s a registered dietitian at Mercy Medical Center in Baltimore.

But there are certain groups who may be more vulnerable to a K deficiency, she adds. They include:

  • Newborn infants. Babies are believed to be born with a sterile intestinal tract, says Morey: “So it takes several weeks for the bacteria that produce vitamin K to become established.” That’s why babies are often given a dose of vitamin K at birth.
  • People with gastrointestinal disorders. If you have a disease such as celiac disease, ulcerative colitis or short bowel syndrome, your body may not be able to absorb vitamin K properly. That’s according to the National Institutes of Health.
  • Certain medications. Using antibiotics for more than several weeks can destroy vitamin K–producing bacteria in your gut. Two cholesterol medicines, cholestyramine (Questran®) and colestipol (Colestid®), can also make it hard for your body to absorb vitamin K. (Check out other cholesterol medications that may work better for you.)
  • Age. “Some research suggests that older adults have a greater likelihood of becoming vitamin K–deficient,” says Dyckman. “They may not be eating a balanced diet, or they may simply not absorb nutrients such as vitamin K as efficiently as younger people.”

If you think you’re not getting enough vitamin K, talk to your doctor about testing for a deficiency. That’s done with blood tests that measure the vitamin K in your blood and how quickly your blood clots.

If you are deficient, you’ll likely be given phytonadione, a form of vitamin K, either by mouth or a shot. This medication is also sometimes given to people who are taking other medications known to cause a vitamin K deficiency.

(We asked a pharmacist: “Are prescription supplements better than the ones you buy over the counter?”)

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How to get enough vitamin K

There are 2 types of vitamin K: phylloquinone (vitamin K1) and menaquinone (vitamin K2). You need both to stay healthy, says Dyckman. Between the 2 forms, adult men should get at least 120 micrograms a day. And women should get at least 90 micrograms, according to the National Institutes of Health.

Good sources include the following:

  • Vitamin K1: kale, spinach, broccoli, brussels sprouts, cabbage, lettuce, collard greens and turnip greens
  • Vitamin K2: meat, dairy foods, eggs and natto (fermented soybeans)

Since vitamin K is fat-soluble, it helps to eat vitamin K–rich vegetables alongside a healthy source of fat such as olive oil or avocado. This can help you absorb it better.

But if you’re on the blood-thinning medication warfarin (Jantoven®), talk to your doctor before adding more vitamin K foods to your diet, according to University of Michigan Health.

Since warfarin makes your blood clot more slowly, your doctor may need to change your dose to fit your diet changes. Your doctor may also suggest switching to a blood-thinning medication such as apixaban (Eliquis®) or rivaroxaban (Xarelto®). Those aren’t affected by vitamin K.

To pay less for your prescriptions, print a copy of our free discount card. Then show it to the pharmacist at checkout to see if you can get an instant discount.

Additional sources
Mortality risk associated with low vitamin K:
American Journal of Clinical Nutrition (2020). “Vitamin K status, cardiovascular disease, and all-cause mortality: a participant-level meta-analysis of 3 US cohorts
Vitamin K overview: Harvard T.H. Chan School of Public Health
Low vitamin K increases risk of hip fracture: Bone (2020). “Serum vitamin K 1 (phylloquinone) is associated with fracture risk and hip strength in post-menopausal osteoporosis: A cross-sectional study
Heart disease is the leading cause of death in the U.S.: JAMA (2020). “The Leading Causes of Death in the US for 2020
Vitamin K fact sheet: National Institutes of Health
Vitamin K deficiency overview: Merck Manual
Recommended vitamin K intake: National Institutes of Health