Vitamin K is a fat-soluble nutrient that comes in different forms, primarily Vitamin K1 and Vitamin K2, and plays a role in blood clotting, bone health and cardiovascular health. A lack of vitamin K can lead to deficiency and depletion, with some of the signs of vitamin K deficiency being particularly unpleasant.
Vitamin K deficiency in adults is rare, but it's common in newborn infants because vitamin K does not cross the placenta, and breast milk contains only a small amount. The limited amount of blood clotting proteins at birth increases the risk of bleeding in infants, so a single dose of vitamin K is usually given to all newborns to help prevent vitamin K deficiency bleeding.
While vitamin K deficiency in adults is uncommon, those who may be at higher risk include:
Those taking medications that interfere with vitamin K metabolism, like antibiotics. Antibiotic medicines may destroy vitamin K-producing bacteria in the gut, resulting in potentially decreasing vitamin K levels, especially if taking the medicine for more than a few weeks.
People with digestive conditions like coeliac disease, ulcerative colitis or Crohn's disease that decrease the amount of vitamin K their body absorbs.
People who have had bariatric (weight loss) surgery.
Signs of vitamin K deficiency
The most common signs of vitamin K deficiency are:
Excessive bleeding (as the blood will no longer clot)
Blood in the urine or stool
Reduced bone strength, leading to osteopenia or osteoporosis
Vitamin K sources
Vitamin K1 is primarily found in plant foods and is most abundant in leafy greens including kale, spinach, collards, as well as broccoli, Brussels sprouts, cauliflower and cabbage.
The best sources of vitamin K2 are found in animal products and fermented products. The richest sources of K2 are natto (a fermented soy product popular in Eastern Japan) and goose liver. Other great sources include cheese, egg yolks, and meat like liver, chicken and beef.
Being that vitamin K is fat-soluble, full-fat dairy products (such as milk, yogurt, cheese, and cottage cheese) contain much more K than reduced-fat ones, and nonfat dairy products contain little to no K.
Vitamin K2 supplements
Although vitamin K is abundant in food, it can also be found in supplement form as well. Vitamin K supplements are often combined with other vitamins and nutrients, such as calcium, magnesium or vitamin D.
The amount you need to avoid the signs of vitamin K deficiency may vary based on your age and gender. Adults need approximately 1mg a day of vitamin K for each kg of their body weight. Taking 1mg or less of vitamin K supplements a day is unlikely to cause any harm.
In order to avoid the signs of vitamin K deficiency, the current recommendation for total vitamin K is 90 μg/day for adult women and 120 μg/day for adult men. In a typical diet, most of this would come from K2.
People who are taking warfarin or any other anticoagulant medications related to it should be careful of the amount of vitamin K foods they eat, and not make any changes to their vitamin K intake.