vitamin K - essential to human health

Is Vitamin K Safe?

Vitamin K safety, drug interactions, and effects on lab tests.

Taking vitamin K supplements and ingesting vitamin K in your food is generally considered safe for adults and children. Both vitamin K1 and vitamin K2 have been used safely in clinical trials, including long-term clinical studies (up to 3 years) and intravenously. Not enough studies have been done in pregnant women to determine its safety for fetuses, so pregnant women should seek the advice of their doctor before taking vitamin K supplements.(1412)

Allergic reactions have been reported with injectable vitamin K and are generally mild. However, on very rare occasions, intravenous vitamin K has been linked to potentially fatal allergic reactions. Vitamin K3 is no longer used to treat vitamin K deficiency because it has caused liver toxicity, jaundice, and anemia in infants.(1412)

Vitamin K, VKDB, and Childhood Cancers

Vitamin K deficiency bleeding (VKDB) is a life-threatening condition that causes hemorrhaging in newborn babies. It's easily treated with an injection of 0.5-1 mg of vitamin K.(412)

Two studies in the 1990s reviewing case data suggested that vitamin K injections given to newborn infants were possibly linked to childhood cancers (e.g., leukemia). However, they have since been refuted by much larger and case-controlled research involving over a million medical records.(4)

The American Academy of Pediatrics continues to recommend vitamin K treatment for newborns at risk of the life-threatening condition VKDB.(412)

Safety Concerns with G6PD Deficiency

G6PD deficiency is a common genetic condition found in millions of people. G6PD enzymes are necessary to protect cells from free radicals. Red blood cells are even more susceptible to free radical damage, and without protection they break down rapidly.(13)

Certain foods, infections, drugs, and natural supplements can trigger episodes of rapid blood cell breakdown (called hemolysis) and anemia. Vitamin K was suspected to be a trigger, and some medical experts caution people with G6PD deficiency to avoid vitamin K.(13, 14)

However, a recent systematic analysis of all clinical studies linking vitamin K to hemolysis found no evidence of harm for vitamin K. Other suspected triggers, such as vitamin C, vitamin E, Gingko biloba, and alpha lipoic acid were also cleared (based on current clinical evidence).(15)

Vitamin K Drug/Supplement Interactions

Vitamin K can have dangerous interactions with certain drugs. Conversely, some medications also affect vitamin K levels in the body. Severe vitamin K deficiency increases risk of serious bleeding because vitamin K is needed for clotting.(1)

Table 3: Drug Interactions with Vitamin K
Drug, Vitamin, or Herb What can happen? Why does it happen?
Antibiotics Moderate vitamin K deficiency.(1)

Some vitamin K is produced from bacteria in the intestines. Antibiotics used to treat infections can kill these bacteria.(1)

The risk of this type of adverse interaction is most likely with prolonged antibiotic use (10 or more days) combined in people with low dietary levels of vitamin K.(1)


Severe vitamin K deficiency and risk of brain hemorrhage in newborn infants.(1)

Rarely, and in combination with other risk factors, may cause clotting to take a longer time in adults taking anticonvulsants.(1)

Certain anticonvulsants stimulate liver enzymes. If taken during pregnancy, these enzymes can cause deficiency in fetuses.(1)

Pregnant women can decrease the risk by taking oral vitamin K supplements (10-20 mg/day) and administration of vitamin K to the baby immediately after birth.(1)

Cholesterol Medication Moderate vitamin K deficiency.(114) Vitamin K is a vitamin that is dissolved and stored in fats. Drugs like Questran® and Colestid® reduce absorption of dietary fats and the vitamin K they contain.(1)
Coenzyme Q-10 Supplements Increase risk of dangerous blood clots.(1) Coenzyme Q10 is chemically similar to vitamin K2. Combining the two can increase the effects of vitamin K, including on reducing the ability of anticoagulant drugs (such as warfarin) to prevent clots.(1)
Mineral Oil Moderate vitamin K deficiency and longer clotting times.(1) Reduces absorption of vitamin K needed for clotting.(1)
Oral Anticoagulants (e.g., warfarin) Excess vitamin K counteracts the anticoagulant effects of these drugs.(1)

Since vitamin K2 has a much longer half-life than vitamin K1, it has more stable levels in the blood. This means a greater chance of adverse interaction with other medications or supplements.(16)

Experts caution that as little as 50 µg/d of vitamin K2 may significantly interfere with anticoagulation drugs.(16)

Orlistat® Weight Loss Drugs and Olestra Moderate vitamin K deficiency.(114)

These diet drugs work by blocking the absorption of dietary fats, which can inhibit absorption of fat soluble vitamin K.(1)

Taking a multivitamin with vitamin K (and other fat soluble vitamins) 2 hours before or after Orlistat may help.(1)

Tiratricol Synthetic Thyroid Hormone May interfere with clotting.(1) Breaks down vitamin K-dependent clotting proteins.(1)
Vitamin A High doses may interfere with clotting.(1) May block the clotting/coagulant its effects of vitamin K.(1)
Vitamin E Doses greater than 800 units per day can inhibit coagulant effects of vitamin K, especially on people taking warfarin.(1) Vitamin E binds to and blocks the activity of vitamin K dependent clotting enzymes. It also reduces absorption of vitamin K.(1)

Vitamin K: Interactions with Lab Tests

Vitamin K may interfere with results of lab tests with a number of substances, either by altering levels of the substance or causing inaccurate results because of interference with the testing mechanism:(117)

Table 4: Vitamin K Effects on Lab Tests
Testing For Test Type Possible Vitamin K Effects
17-Hydroxycorticosteroids Urine False increase.
Bilirubin Blood Increases in bilirubin for newborns or people with enzyme G6PD deficiency.
Calcium Urine Reduces calcium levels.
Hemoglobin Urine Vitamins K3 and K4 can cause decreases in this iron-containing blood cell molecule (especially in people with enzyme G-6-PD deficiency). Conversely vitamin K can increase levels.
Osteocalcin Blood Increases levels in postmenopausal women.
Protein Urine Increases levels.
White Blood Cells & Platelets Blood In patients with pancytopenia, vitamin K3 and vitamin K4 can decrease levels.
Also known as vitamin K1.(1)
Made with fava beans.(13)
Specifically, bile acid sequestrants used to lower cholesterol levels.(14)
Also known as menaquinone-7 and MK-7.(1)
Brand names include Xenical® and alli®.(1)
An ingredient in some foods.(14)
Blood cell deficiencies caused by various conditions or diseases (such as an enlarged spleen or bone cancer).(17)
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