Vitamin K: Key Role, Dosage, Sources & Benefits

Picture of vitamin K on infant

Vitamin K Overview

Vitamin K plays a key role in helping the blood clot, preventing excessive bleeding. Unlike many other vitamins, vitamin K is not typically used as a dietary supplement.

Vitamin K is actually a group of compounds. The most important of these compounds appears to be vitamin K1 and vitamin K2. Vitamin K1 is obtained from leafy greens and some other vegetables. Vitamin K2 is a group of compounds largely obtained from meats, cheeses, and eggs, and synthesized by bacteria.

Vitamin K1 is the main form of vitamin K supplement available in the U.S.

Recently, some people have looked to vitamin K2 to treat osteoporosis and steroid-induced bone loss, but the research is conflicting. At this point there is not enough data to recommend using vitamin K2 for osteoporosis.

Vitamin K is known as the clotting vitamin, because without it blood would not clot. Some studies suggest that it helps maintain strong bones in the elderly.

Food Sources of Vitamin K

The best way to get the daily requirement of vitamin K is by eating food sources. Vitamin K is found in the following foods:

  • Green leafy vegetables, such as kale, spinach, turnip greens, collards, Swiss chard, mustard greens, parsley, romaine, and green leaf lettuce
  • Vegetables such as Brussels sprouts, broccoli, cauliflower, and cabbage
  • Fish, liver, meat, eggs, and cereals (contain smaller amounts)

Vitamin K is also made by the bacteria in the lower intestinal tract.

How much vitamin K do I need?

Adults need approximately 0.001mg a day of vitamin K for each kilogram of their body weight.

For example, someone who weighs 65kg would need 0.065mg a day of vitamin K, while a person who weighs 75kg would need 0.075mg a day.

You should be able to get all the vitamin K you need by eating a varied and balanced diet.

Any vitamin K your body doesn’t need immediately is stored in the liver for future use, so you don’t need it in your diet every day.

Why do people take vitamin K?

Low levels of vitamin K can raise the risk of uncontrolled bleeding. While vitamin K deficiencies are rare in adults, they are very common in newborn infants. A single injection of vitamin K for newborns is standard. Vitamin K is also used to counteract an overdose of the blood thinner Coumadin.

While vitamin K deficiencies are uncommon, you may be at higher risk if you:

  • Have a disease that affects absorption in the digestive tract, such as Crohn’s disease or active celiac disease
  • Take drugs that interfere with vitamin K absorption
  • Are severely malnourished
  • Drink alcohol heavily

In these cases, a health care provider might suggest vitamin K supplements.

Uses of vitamin K for cancer, for the symptoms of morning sickness, for the removal of spider veins, and for other conditions are unproven.

Side Effects – Vitamin K deficiency

Vitamin K deficiency is very rare. It occurs when the body can’t properly absorb the vitamin from the intestinal tract. Vitamin K deficiency can also occur after long-term treatment with antibiotics.

People with vitamin K deficiency are often more likely to have bruising and bleeding.

If you take blood thinning drugs (such as anticoagulant/antiplatelet drugs), you may need to limit vitamin K foods. You may also need to eat a consistent amount of vitamin K containing foods on a day to day basis if you consume these foods. You should know that vitamin K or foods containing vitamin K can affect how these drugs work.

It is important for you to keep vitamin K levels in your blood about the same from day to day. Ask your health care provider how much vitamin K-containing foods you should eat.

What happens if I take too much Vitamin K?

There’s not enough evidence to know what the effects might be of taking high doses of vitamin K supplements each day.

Recommendations for Taking Vitamin K

The Recommended Dietary Allowance (RDA) for vitamins reflects how much of each vitamin most people should get each day.

  • The RDA for vitamins may be used as goals for each person.
  • How much of each vitamin you need depends on your age and gender.
  • Other factors, such as pregnancy, breast-feeding, and illness may increase the amount you need.

The Food and Nutrition Board at the Institute of Medicine Recommended Intakes for Individuals – Adequate Intakes (AIs) for vitamin K:

Infants

  • 0 to 6 months: 2.0 micrograms per day (mcg/day)
  • 7 to 12 months: 2.5 mcg/day

Children

  • 1 to 3 years: 30 mcg/day
  • 4 to 8 years: 55 mcg/day
  • 9 to 13 years: 60 mcg/day

Adolescents and Adults

  • Males and females age 14 to 18: 75 mcg/day
  • Males and females age 19 and older: 90 mcg/day for females (including those who are pregnant and lactating) and 120 mcg/day for males

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