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What is Vitamin K good for? And what to do if you’re deficient

Close to a third of adults could be low in Vitamin K—what that could mean and how to remedy it

Vitamin K is the name given to a group of fat-soluble vitamins that perform a number of key functions in the body. The good news is that most people can get what they need simply by eating a healthy diet.

What is vitamin K good for? 

There are three important reasons our bodies need vitamin K:

  • for strong and healthy bones
  • to enable efficient blood clotting
  • to help combat heart disease (reduces vascular calcification)

Vitamin K is essential for keeping your bones healthy, healing wounds and maintaining your blood vessels. It makes various proteins that are necessary for these functions and is found throughout the body—in the liver, brain, heart, pancreas and bone. It can help prevent broken bones and fractures, especially in post-menopausal women, and it can also be useful in the treatment of cancer, osteoarthritis and diabetes.

What are the main sources of vitamin K?

There are two important forms. The main source of vitamin K is phylloquinones, also known as K1. This can be found in leafy green vegetables, such as:

  • Kale
  • Spinach
  • Broccoli
  • Brussels sprouts
  • Cabbage
  • Lettuces
  • Collard greens
  • Turnip greens
  • Soybean and canola oil
  • Salad dressings made with soybean or canola oil
  • Fortified meal replacement shakes

Other foods that have vitamin K include menaquinones, the second form, which is known as K2. These can be found in:

  • Some fermented foods, including soybeans
  • Meat, butter, cheese and egg yolks—though in smaller amounts published this helpful list of 20 foods that are high in Vitamin K. You’ll note that leafy green vegetables are far and away the foods that are highest in vitamin K, though it can be found in smaller amounts in certain meat products (bacon – 25% of the recommended daily value per serving), cheese (Jarlsberg – 19%) and fruit (blackberries, blueberries and pomegranates – 12%).

TIP: It is best to eat Vitamin K-rich foods with a small amount of fat, such as butter or oil, as this will improve the absorption of nutrients. Try drizzling some olive oil on your favourite salad or adding some diced avocado to your meal, for example.

How much Vitamin K do I need?

There hasn’t been enough evidence to establish a Recommended Dietary Allowance (RDA) of Vitamin K. Instead, adequate intake (AI) is used as the measure. For adults aged 19 and older, the AI is 120 micrograms (mcg) daily for men and 90 mcg for women. For women who are pregnant or breastfeeding, the number is also 90 mcg. 

Which vitamin K is best?

Most people get enough vitamin K in their diet, so taking supplements isn’t necessary, according to Unlockfood. If you don’t have enough leafy green vegetables in your diet, it’s possible that you may need to supplement, but it’s best to check with your doctor first. The amount of vitamin K found in most supplements tends to be much higher than what is recommended, so it’s important to follow your doctor’s advice.

If you’re feeling daunted by the thought of eating so many leafy greens, just slip some into your favourite dishes; they work really well in soups, casseroles and omelettes. Making a sandwich? Forget the iceberg lettuce and instead opt for spinach, romaine lettuce, mustard, beet or turnip greens. These small additions and substitutions add up quickly.

What happens if your vitamin K is too high?

Fortunately, this isn’t one of the vitamins you have to worry about taking too much of.

The body breaks down vitamin K very quickly, excreting it in the urine or stool. Because it is so efficient at doing this, reaching toxic levels (even with high intakes) is rare, according to the T.H. Chan School of Public Health at Harvard.

The only people who may need to exercise caution is anyone who takes a blood-thinning medication called warfarin; too much vitamin K can interfere with this medication’s efficacy.

Who is most at risk for vitamin K deficiency?

Vitamin K deficiency is very rare, according to the National Institutes of Health.

It can, however, occur in anyone who takes medications that block vitamin K metabolism, such as antibiotics, or in those who have conditions that interfere with the absorption of nutrients from food.

People with malabsorption syndromes and other gastrointestinal disorders often have issues absorbing vitamin K properly. Anyone who has cystic fibrosis, celiac disease, ulcerative colitis or short bowel syndrome, or who has undergone bariatric surgery, may be low in the vitamin. In this case, their status may need to be monitored by a doctor and supplementation could be required.

A deficiency can also be possible in newborn infants. That’s because breast milk only contains a low amount and vitamin K does not cross the placenta. Because few blood clotting proteins are present at birth, infants are at increased risk of bleeding if they are not given vitamin K supplements. In Canada, infants usually receive a vitamin K injection at birth.

How do I know if I need vitamin K?

A study done in Nutrients revealed that up to 31 percent of the adult population may be insufficient in vitamin K.

The biggest signs to look out for include:

  • wounds that don’t clot quickly
  • easy bruising
  • excessive bleeding (heavy menstrual periods, nose bleeds, blood in the urine or stool, bleeding gums)

Losing bone strength, experiencing heart issues and having arthritis symptoms are some of the other possible warning signs, according to   

To know for sure, have your doctor determine your vitamin K levels via a blood test. That’s the best way to know if you need to up your dietary intake—and to rule out any other possible issues.