Vitamin K: Everything You Need to Know

Vitamin K: Everything You Need to Know
02.04.2024

Vitamin K is a collective term for a group of compounds with a similar chemical structure. These compounds are essential for skeletal health, blood clotting, and many other important functions in the body.

The types of vitamin K obtained from dietary sources include vitamin K1 (phylloquinone), which is concentrated in plant foods, and several types of vitamin K2 (menaquinones), which are found in animal products and fermented foods. Vitamin K can also be taken as a dietary supplement. 

Most people most people get plenty of vitamin K through their diet, but some people require vitamin K supplements.

Here’s what you need to know about vitamin K supplements, including their benefits, safety, side effects, and what to look for when shopping for a vitamin K supplement. 

Benefits of Vitamin K  

Vitamin K1 is the primary dietary form of vitamin K and is found in certain vegetables, like spinach and broccoli, as well as certain fruits, herbs, and oils. Vitamin K2 is created by bacteria and is concentrated in animal products like meat and dairy, and fermented foods like natto.

Most forms of K2 are also produced by gut bacteria, which covers some of your daily vitamin K requirements.

Vitamin K can also be taken in supplemental form. It’s a common ingredient in multivitamins and multi-nutrient formulations designed to support bone health. Vitamin K-only supplements are also available for purchase.

There are several forms of vitamin K used in supplements, including K1 (phylloquinone), a synthetic form of K1 called phytonadione, and vitamin K2 as MK-4 or MK-7.

Vitamin K deficiency is very rare in the United States, and most Americans get plenty of vitamin K through their diet. However, some populations, such as people who can’t properly absorb vitamin K in their digestive tract, may require supplemental vitamin K.

In addition to being necessary for certain people, vitamin K supplements have been shown to benefit health in several ways.

Supports Bone Health 

The body needs Vitamin K for the function of proteins involved in bone health maintenance. Certain proteins in the bones depend on vitamin K to bind to calcium. For example, vitamin K is needed for the function of osteoblasts, which are cells that build new bone.

You need sufficient levels of vitamin K to maintain healthy bones. Low intake of vitamin K may increase the risk of bone issues, such as low bone mineral density and fracture risk.

Some research suggests that taking vitamin K supplements may help prevent fractures in at-risk populations. A review of 20 studies found that postmenopausal and osteoporotic participants who supplemented with vitamin K had a lower fracture risk compared to people who didn’t take vitamin K supplements.

Some studies’ findings suggest that vitamin K supplements may improve bone mineral density in certain areas of the body, including the lumbar spine.

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However, not all studies have found a clear benefit and more research is needed to understand how vitamin K supplements impact bone density.

Protects Heart Health

Vitamin K benefits heart health in several ways. The body needs Vitamin K for the activation of several proteins that inhibit the buildup of calcium in blood vessels, which can help prevent heart disease.

Arterial calcification contributes to atherosclerosis, a term used to describe the thickening or hardening of the arteries caused by a buildup of plaque. Atherosclerosis is the main cause of heart disease.

Vitamin K also helps improve the elasticity of arteries, which support and protect heart health.

A recent review that included 14 studies found that vitamin K supplementation significantly reduced coronary artery calcification scores and slowed the progression of coronary artery calcification.

Additionally, studies suggest that diets high in vitamin K2 may lower the risk for developing coronary heart disease, the most common type of heart disease in the U.S.

May Support Blood Sugar Regulation

Insulin is a hormone that helps shuttle blood sugar into cells where it can be used for energy or stored for later use. Osteocalcin, which is dependent on vitamin K, stimulates insulin secretion from the pancreas and enhances the insulin sensitivity of muscle cells.

Studies show that people who consume vitamin K-rich diets have better blood sugar control and are more sensitive to insulin compared to people with lower vitamin K intakes.

Other research suggests that supplementing with vitamin K may enhance insulin sensitivity and blood sugar control in certain populations.

A recent study that included 60 people with type 2 diabetes found that, compared to a control group, participants who supplemented with 90 micrograms (mcg) of MK-7 per day for six months experienced 13.4%, 28.3%, and 7.4% reductions in fasting blood sugar, insulin, and the long-term blood sugar control marker hemoglobin A1c (HbA1c), respectively.

May Improve Certain Medical Conditions

Vitamin K supplements may benefit specific populations, including people with certain medical conditions. For example, people with diseases that impact the absorption of fat-soluble nutrients, like vitamin K, may require supplements to maintain healthy blood levels of this nutrient.

Diseases that impact vitamin K absorption include celiac disease, ulcerative colitis, cystic fibrosis, and short bowel syndrome.

Studies also suggest that vitamin K supplements may improve disease progression in people with certain neurological disorders, such as multiple sclerosis and Alzheimer’s disease.

Good Sources of Vitamin K

Vitamin K is found in a number of foods. Vitamin K1 is primarily concentrated in plant foods, while K2 is found in animal foods and fermented products.

Here are some of the best dietary sources of vitamin K:

  • Natto: 850 mcg per 3 ounces, or 708% of the Daily Value (DV)
  • Collard greens: 530 mcg per ½ cup, or 442% of the DV
  • Spinach (raw): 145 mcg per cup, or 121% of the DV
  • Broccoli: 110 mcg per cup, or 92% of the DV
  • Roasted soybeans: 86 mcg per cup, or 72% of the DV
  • Canned pumpkin: 40 mcg per cup, or 34% of the DV
  • Chicken breast: 13 mcg per 3 ounces, or 11% of the DV
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Vitamin K is also found in smaller amounts in grapes, cashews, olive oil, beef, and several other foods.

How to Take Vitamin K

Vitamin K is found in a number of dietary supplements, such as multivitamins and bone health supplements. It’s often combined with other nutrients required for skeletal health, such as vitamin D and calcium. Most multivitamin supplements provide less than 75% of the DV for vitamin K per dose, while vitamin K-only products can contain very high amounts of vitamin K, far exceeding the DV.

Vitamin K works synergistically with certain nutrients. For example, vitamin K and vitamin D work together in the body, and some study findings suggest that joint supplementation with vitamin K and vitamin D is more beneficial for bone and heart health than supplementing with vitamin D alone.

Few studies have investigated the absorbability of the forms of vitamin K used in dietary supplements. However, phytonadione and MK-7, two forms of vitamin K commonly used in dietary supplements, seem to be well-absorbed.

Vitamin K is a fat-soluble nutrient, meaning it may be better absorbed with a meal or snack containing fat.

Dosage 

The current adequate intake (AI) for vitamin K is 120 mcg for adult men and 90 mcg for adult women, including people who are pregnant or breastfeeding. This accounts for total dietary intake, including vitamin K derived from foods and supplements.

Dosing for vitamin K varies depending on the type of vitamin K used. Some supplements provide 75% or less of the DV for vitamin K, while others provide over 1,000% of the DV per serving.

It’s important to ask your healthcare provider about vitamin K dosing so you can choose the best form and dose of vitamin K for your health needs.

Is Vitamin K Safe?

Vitamin K is considered a safe supplement with low potential for toxicity. For this reason, the Food and Nutrition Board (FNB) has not established a Tolerable Upper Intake Level (UL) for vitamin K supplements. A UL is the maximum daily intake of a nutrient unlikely to cause harm.

However, it’s important to always follow dosing directions and consult your healthcare provider if you have any questions regarding vitamin K dosing.

Potential Drug Interactions

Although vitamin K supplements are considered safe, they have the potential to interact with some medications. Plus, taking certain medications can deplete vitamin K levels. These include:

  • Blood-thinning medications. Vitamin K supplements may interact with blood thinners like Warfarin. These medications can inhibit the blood clotting effects of vitamin K, which can increase bleeding risk. People who are on blood thinners should maintain a consistent intake of vitamin K, including dietary sources of vitamin K and supplements, as sudden changes in your intake could increase the risk of bleeding or blood clots.
  • Antibiotics. Certain antibiotics can impact vitamin K production in the gut, which can increase the risk of developing low vitamin K levels. If you’re taking cephalosporin antibiotics, such as cefoperazone (Cefobid), for more than a few weeks, you may need to take a vitamin K supplement.
  • Some cholesterol medications. Bile acid sequestrants, which are used to treat high cholesterol levels, may reduce the absorption of fat-soluble vitamins like vitamin K. People who take bile acid sequestrates should have their vitamin K levels monitored.   
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Additionally, the weight loss medication orlistat (Alli) has been shown to reduce the absorption of fat-soluble nutrients. If you’re taking orlistat, your healthcare provider may recommend taking a multivitamin containing fat-soluble nutrients, like vitamin K.

What to Look For 

It’s best to purchase vitamin K supplements from trusted companies. Many supplement companies are certified by third-party organizations like U.S. Pharmacopeia and NSF International, which helps ensure supplement safety and quality.

When shopping for a vitamin K supplement, it’s important to choose a product based on your health needs. For example, a multivitamin containing vitamin K may be best for those looking for overall nutritional support while a supplement that contains vitamin K and other bone-supportive nutrients, such as vitamin D and magnesium, may be better for a person with osteoporosis or increased fracture risk.

If you have sensitivities or allergies, make sure to purchase a vitamin K supplement that’s free from potential allergens like gluten, soy, and tree nuts.

Side Effects of Vitamin K

Vitamin K supplements aren’t associated with side effects and have a very low potential for toxicity.

A few research studies investigating the health effects of vitamin K supplements have reported minor reactions, such as gastrointestinal upset and skin reactions. However, in general, vitamin K supplements aren’t associated with adverse side effects.

Takeaway Note

Vitamin K is the collective term for a group of fat-soluble compounds with similar structures. Vitamin K plays many important roles in the body and is needed for bone and heart health, blood clotting, and more.

Some studies show that supplementing with vitamin K may help reduce fracture risk and improve heart health in certain populations. Vitamin K supplements may also be helpful for people with certain medical conditions, such as multiple sclerosis and celiac disease.

If you’re interested in taking a vitamin K supplement, consult your healthcare provider to learn if it’s the right choice for your specific health needs.

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