What comes to mind when you think about vitamins and minerals for bone health? You might automatically think of calcium and vitamin D as the top bone-building nutrients. But there's another less talked-about nutrient that's just as important for keeping your bones healthy and strong: vitamin K.
Vitamin K is a fat-soluble vitamin—meaning it’s stored in fat in your body instead of excreted in urine— that's found in many foods. It's also made by the good bacteria in your gut. Vitamin K is essential for many aspects of health, including maintaining strong bones.
Let's explore the role of vitamin K in bone health, how much you need each day, and the best food sources of this vital nutrient.
What Is Vitamin K?
Vitamin K is an essential vitamin needed for blood clotting, bone health, and more. It's found in food but can also be made by bacteria in the intestines (more on this below)
There are several forms of vitamin K, but the two main ones are vitamin K1 and K2.
- Vitamin K1, also known as phylloquinone, is found mainly in plants. It's the primary form found in your food and is also used by the body for blood clotting (Palermo, 2017).
- Vitamin K2 refers to a group of compounds known as menaquinones. Menaquinones are made by bacteria in the intestines. It's also found in animal foods like liver and some fermented foods (Akbari, 2018).
Research suggests that vitamin K2 is slightly more bioavailable, meaning your body can absorb and use it more easily (Beulens, 2013).
How Does Vitamin K Support Bone Health?
There are several ways that vitamin K helps with keeping bones strong:
- Acts as a coenzyme. Coenzymes are helper molecules that are needed for enzymes to do their job. Vitamin K is required for an important enzyme called gamma-glutamate carboxylase to work (Wen, 2018). This enzyme is needed to synthesize osteocalcin, a protein essential for bone strength (Zoch, 2016).
- Regulates calcium metabolism. Vitamin K helps control how much calcium is in the blood and how much is stored in the bone. It helps keep calcium levels in the blood within a healthy range and prevents too much calcium from being deposited in the arteries, which can lead to heart disease (Maresz, 2015).
- Regulates genes for bone building and breakdown. Bone is constantly being remodeled, which means old bone is broken down and new bone is produced. This process is regulated by genes, and vitamin K has been shown to influence the activity of these genes (Rodríguez-Olleros Rodriguez, 2019).
The evidence is clear: Low vitamin K levels are associated with an increased risk of fractures (Rodríguez-Olleros Rodriguez, 2019). Some research suggests that women with the highest intakes of vitamin K have a much lower risk of fractures compared with lower intakes (Hao, 2017). Meanwhile, low dietary vitamin K levels are linked to lower bone mineral density (BMD), specifically for women (Booth, 2003).
The synergistic effect of bone nutrients makes vitamin K even more helpful for bones. For example, a study examining healthy women without osteoporosis found that those who ate adequate levels of vitamin K while supplementing with vitamin D and calcium improved their BMD of the distal radius (a bone found in the forearm) (Bolton-Smith 2007).
What Foods Contain Vitamin K?
Vitamin K is found in leafy green vegetables, such as:
- Kale
- Spinach
- Collard greens
- Broccoli
- Brussels sprouts
- Cabbage
Other sources of vitamin K include:
- Liver
- Edamame
- Canned pumpkin
- Natto (a Japanese fermented soybean dish)
- Soybeans
Since vitamin K is fat-soluble, consuming vitamin K-rich foods as part of a complete meal is a great way to promote optimal absorption.
A note about dark leafy greens:
Dark leafy greens contain compounds called oxalates. Oxalates bind to calcium during digestion and prevent some of it from being absorbed. As adequate calcium absorption is pivotal to bone health, the question has arisen whether eating dark leafy greens, which are very nutrient-dense and generally beneficial, should be avoided to prevent inadequate calcium absorption. It is important to recognize that the oxalates in spinach reduce absorption of calcium only from the spinach itself. If spinach is eaten with cheese, the calcium will be absorbed normally from the cheese. Spinach has many nutritional benefits for people with osteoporosis as well as those without, but it should not be considered a good source of calcium. Greens such as kale have a lower oxalate concentration and are therefore a better source of calcium.
Moral of the story: The benefits of eating dark leafy greens outweigh the negatives.
How Much Vitamin K Do You Need?
The adequate intake (AI) for vitamin K is 120 micrograms/day for adult men 19 and older and 90 micrograms/day for women (National Academies Press (US); 2001.)
A serving of dark leafy greens can nearly meet your daily needs for vitamin K. For example, one cup of raw kale contains about 82 micrograms of vitamin K, and a cup of raw spinach contains 145 micrograms.
Sometimes supplements help people get enough vitamin K, especially if they have a medical condition like liver or inflammatory bowel disease (Rodríguez-Olleros Rodriguez, 2019). If you're considering taking a supplement, talk to your doctor first, as vitamin K can interfere with certain medications.
How To Add More Vitamin K To Your Diet
Need a little help with adding more vitamin K to your diet? Try this:
- Add kale or spinach to your morning smoothie
- Throw some Brussels sprouts on your lunchtime salad
- Sauté kale and other leafy greens as a side dish for dinner
- Make a healthy stir-fry for lunch or dinner with chicken, broccoli, and soybeans
If you're feeling adventurous, you can also try natto to boost your vitamin K2 intake. The taste, texture, and smell of natto may take some getting used to, but it's loaded with nutrients.
And don't forget to consume vitamin K-rich foods in meals that include some fat (butter, oil) to help your body absorb the vitamin K.
Vitamin K is an essential nutrient for your bones, but it's not the only one. A well-rounded diet that includes a variety of nutrient-rich foods is the best way to support your bones. Add in physical activity and weight-bearing exercises, and you'll be on your way to strong, healthy bones for life.
