Do you need Vitamin K in a Multivitamin? (4 min.)

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Vitamin K supports blood clotting and plays a role in bone metabolism†, but it’s not included in all multivitamins due to its interactions with certain medications, such as blood thinners.

At Cooper Complete, we offer a one-a-day multivitamin with iron and an iron-free version, both formulated without vitamin K. For those looking to include vitamin K in their supplement routine, we offer a comprehensive multivitamin that includes vitamin K.

Vitamin K Function in the Body

Vitamin K’s primary function is to regulate blood clotting, helping the body produce proteins necessary for coagulation. A deficiency may result in easy bruising or frequent nosebleeds due to impaired clotting†.

Vitamin K absorption may be reduced in individuals with certain gastrointestinal conditions such as colitis, sprue, cystic fibrosis, or Crohn’s disease†. Long-term use of antibiotics or anticoagulant  therapy can also interfere with vitamin K synthesis and absorption†. People with liver disorders or alcohol dependency are also at greater risk for deficiency.

Blood Thinners and Pregnancy

Vitamin K is a significant concern for people taking Warfarin (a blood thinner), as vitamin K can affect the drug’s effectiveness. For this reason, the Basic One multivitamin and mineral formulations do not contain vitamin K.

Physicians may recommend increased vitamin K for people prone to bruising, especially pregnant women, although excess intake during the final stages of pregnancy may pose a health risk to the developing fetus. Always consult your doctor before taking vitamin K supplements.

Forms of Vitamin K

There are three primary forms of vitamin K:

• K1 (phylloquinone): Found in green, leafy vegetables like lettuce, broccoli and spinach, and in olives and some vegetable oils.
• K2 (menaquinone): Found in fermented soybeans (natto), some cheeses, liver, and eggs.
• K3 (menadione): A synthetic not used in human supplements in the U.S., although it is sometimes included in pet food and livestock feed.

Vitamin K1 accounts for about 90 percent of the vitamin K in the average Western diet. K2 is less commonly consumed, but it is gaining attention for its benefits to bone and heart health†.

Vitamin K2 and Bone Health†

Vitamin K2 (menaquinone) is of particular interest for bone health†. It helps activate proteins that bind calcium to bones, potentially improving bone strength and reducing fracture risk†. Some research suggests K2 works synergistically with vitamin D and calcium†. These effects could be particularly beneficial for postmenopausal women and older adults at risk for osteoporosis†.

While vitamin K2 is more expensive to produce and less commonly found in multivitamins, it’s an important nutrient to consider for comprehensive bone support.

Vitamin K Needs and Storage in the Body

Overall, the body stores very little of this vitamin. Small amounts are deposited in the liver and bones to meet the needs for a few days. Most Americans get enough or almost enough K in their diet. However, the NIH has not established a recommended daily allowance (RDA) for vitamin K but has provided Adequate Intake (AI) levels.

Most people consume sufficient amounts of vitamin K1, but intake of vitamin K2 is low, as it’s found in fermented foods (like natto) that aren’t commonly eaten in the U.S.

Vitamin K and Infants

Vitamin K deficiency in newborns can result in vitamin K deficiency bleeding (VKDB). Newborns typically have low vitamin K stores, and the vitamin K cycle may not function well in premature infants. Breast milk is also low in vitamin K, and infants whose mothers are taking certain medications (like anticonvulsants) may be at higher risk for deficiency.

For these reasons, it’s common for newborns to receive a vitamin K injection shortly after birth.

Summary

Vitamin K plays a crucial role in both blood clotting and bone health. While most people get enough K1 from vegetables, K2 intake may be lacking in typical Western diets. People taking anticoagulants or with specific health conditions may need to avoid vitamin K, while others may benefit from supplementing with it.

Cooper Complete offers multivitamins, both with and without vitamin K, to suit individual health needs. (Cooper Complete Basic One and the Cooper Complete Healthy Body Pack do not contain vitamin K.)

As always, consult with your physician or health care provider about your specific health issues before making any changes to your supplement routine.

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About the Author: Jill Turner is the President of Cooper Complete® Nutritional Supplements, where she oversees product development and customer experience. She enjoys writing about vitamins, supplements, and preventive health to help consumers make informed, science-backed decisions.

Cooper Complete July 8, 2025