Vitamin K Facts: Everything You Need to Know
Medically Reviewed by Dr. Samantha Miller, MBChB
Vitamin K is often mentioned in health and wellbeing media, and it’s common to see it addressed in respect to various health claims — from anti-aging effects and healthy skin to bone health and a lower risk of cardiovascular disease. But what does this vitamin really do, where can you find it and are you getting enough? Read on to learn all the essential basics you’ll want to know about vitamin K.
What Does Vitamin K Do?
Vitamin K's name originates from the German word "koagulationsvitamin" ("coagulation vitamin" in English), which refers to the process of blood clot formation. And it’s fitting — one of the most important of vitamin K’s roles is that it helps blood clot properly. Without vitamin K, small cuts on your arm could prove to be lethal because the flow of blood wouldn’t stop.
Vitamin K may also play a role in the maintenance of healthy bones. It’s a cofactor required for the mineralization process of bones, along with calcium and vitamin D. These three substances work together to strengthen the structure of bones. Some studies have suggested that a higher intake of vitamin K correlates with a higher bone mineral density and a lower risk of damage such as fractures. However, adequate intake of calcium and vitamin D are likely to have a much greater role in bone health, and it’s not clear if supplementing vitamin K has any effect on bone health for people with a healthy diet and no underlying conditions.
Some studies have also suggested that vitamin K can help prevent hardening of the cardiovascular system due to calcification, which is a process that results in excessive calcium buildup in soft tissues, arteries and heart valves. This means that getting enough vitamin K can help protect your heart and blood from diseases, such as stroke and heart attack, later in life. Because most people get enough vitamin K from their diets alone, though, there’s no formal recommendation to use vitamin K supplements to achieve these potential cardioprotective benefits.
Research on vitamin K suggests some laboratory-based anti-inflammatory and anti-aging properties. That’s because it serves as a cell-signaling nutrient that may help prolong cell life. In fact, many cosmetic scar treatment gels boast that they use vitamin K as a main ingredient due to its cell-strengthening properties. Because it protects the nervous system, liver, lungs, heart, cartilage, stomach and kidneys, vitamin K may also potentially be effective in preventing some degenerative and fatal conditions, including Alzheimer's disease and liver cancer. However, overall, there’s insufficient evidence to suggest taking extra vitamin K is beneficial in any of these conditions.
Food Sources of Vitamin K
When you do need to supplement it, vitamin K is readily available via a diverse selection of food sources. Specifically, the forms of vitamin K found in naturally occurring food sources are K1 and K2. The most prominent sources of the nutrient are dark-colored cruciferous vegetables, which includes brussels sprouts, Swiss chard, broccoli, kale and mustard greens. Other colorful vegetables, such as spinach, green beans, asparagus, romaine lettuce, tomatoes and peas, are also rich sources of the vitamin.
Several fermented foods contain high levels of vitamin K, since some strains of bacteria that facilitate the fermentation process are also vitamin K-generating. For example, the Propionibacterium genus of bacteria found in Swiss and Jarlsberg cheeses generates abundant amounts of vitamin K. Fermented soy products, such as soybean paste and Japanese natto, have a strain of B. subtilis that produces abundant amounts of vitamin K.
Vitamin K is also available as a dietary supplement. Usually, a daily multivitamin will contain the recommended daily amount. The synthetic form of vitamin K is also known as K3, or menadione. Taking 1mg or less per day of vitamin K as a supplement is unlikely to be harmful.
Can You Get Too Much (or Too Little) Vitamin K?
Vitamin K in excess is stored in the liver, so you don’t need to get it from your diet every single day. But because vitamin K is very important for blood coagulation, a deficiency in the nutrient can lead to problems with blood clotting. When someone’s blood doesn’t have clotting factor, a small cut on the finger, or even a bruise, can be fatal. The nutrient also plays a prominent role in regulating calcium, so too little vitamin K can lead to hardening of the arteries due to calcification and can also weaken bones. A deficiency in infants may lead to malformation of cartilage and bone structure.
Signs and symptoms of vitamin K deficiency in adults may include uncontrollable bleeding, excessive bruising, petechiae (a multitude of small red dots that are bleeding sites under the skin) and cartilage calcification. Sometimes, a vitamin K deficiency may be a sign of absorption problems in the intestines. If left untreated, these symptoms can be life-threatening, as too little vitamin K has also been linked to serious medical problems later in life.
So far, overdosing on vitamin K1 and K2, which both come from naturally occurring sources, has not been documented, so medical professionals haven’t established a tolerable upper level of the vitamin. The only documented instances of vitamin K poisoning stem from synthetic forms of the nutrient, known as menadione or vitamin K3, which is found in vitamins and supplements. Excess menadione can lead to damage to cell membranes, liver toxicity, jaundice and anemia. Vitamin K supplements can also interact with other supplements, such as coenzyme Q10, which may predispose you to dangerous clotting abnormalities.
It’s recommended that all newborns receive a shot of vitamin K shortly after birth. This is because vitamin K doesn’t cross the placenta well, and newborns can become deficient. This can lead to a condition called vitamin K deficiency bleeding (VKDB).
How Much Vitamin K Do You Need?
The U.S. Dietary Reference Intake (DRI) for vitamin K for healthy adults assigned male at birth is 120mcg per day. For healthy adults assigned female at birth, the recommended intake is 90mcg per day. If you’re taking other medications or have a pre-existing medical condition, be sure to consult your physician for a professionally recommended amount of vitamin K supplementation. The nutrient may interact negatively with medications or with your body due to your condition.
Provided you follow a typical healthy diet and don’t have any underlying health conditions, there’s generally no need to take vitamin K supplements. It’s important to maintain a healthy and balanced diet so your body obtains necessary vitamins and minerals. If you’re worried that you may not be getting adequate nutrition, speak to your primary care provider to rule out underlying causes before you start taking over-the-counter supplements — which may not help, and may even be harmful.