Vitamin K and Natto - What's the Connection?

Natto is one of the richest sources of vitamin K2, which is important for bone and heart health. Here's what you need to know about this little-known nutrient and even lesser-known food source. 

Monica Reinagel, MS, LD/N, CNS
4-minute read
Episode #273

Nutrition Diva listener Janet writes:

"I was doing some internet research on foods that promote bone growth and came across a food called natto, which is supposed to be a good source of vitamin K2. My doctor had never heard of natto or vitamin K2.  Is natto really a superfood for bone health and, if so, what's the best way to serve it?".


What Is Vitamin K?

Although vitamin K was identified in the 1920s, right around the same time as vitamins C and E were discovered, it doesn't have anywhere near the name recognition as other nutrients. It was first identified by German researchers who discovered that it was essential for proper blood-clotting. The "K" stands for "koagulation."  

Without this nutrient in your system, you might bleed to death. Later, it was discovered that vitamin K also plays an important role in bone formation (something I talked about in episode #853, Diet for Healthy Bones) as well as heart health.

The Different Forms of Vitamin K

 In terms of helping to build healthy bones and other health benefits, vitamin K2 is thought to be the more potent form. 

Vitamin K is actually a family of closely related compounds. Vitamin K1, also known as phylloquinone, is the form that's found in vegetables, in particular, leafy greens like kale, collards, and spinach. Vitamin K2, also known as menoquinone, is a form produced in animal tissues. In terms of helping to build healthy bones and other health benefits, vitamin K2 is thought to be the more potent form. 

Where Do You Get Vitamin K2?

The good news is that there are lots of potential sources for vitamin K2:

  • Your body will convert some of the vitamin K1 that you get from vegetables into K2.  
  • You can get pre-formed vitamin K2 from meat, eggs, and dairy products.
  • The friendly bacteria that live in your intestines synthesize some vitamin K2 for you.
  • Fermented foods, such as yogurt, kefir, and sauerkraut also contain vitamin K2.

See also: Fermented and Cultured Foods


One of the richest food sources of vitamin K2 is a traditional Japanese food called natto. Studies have found that Japanese women who eat two or more servings of natto a week have higher levels of menaquinone in their blood, and significantly fewer hip fractures than European women who do not eat natto. That's not the same as a controlled trial, of course, but it's certainly an interesting observation. 


About the Author

Monica Reinagel, MS, LD/N, CNS

Monica Reinagel is a board-certified licensed nutritionist, author, and the creator of one of iTunes' most highly ranked health and fitness podcasts. Her advice is regularly featured on the TODAY show, Dr. Oz, NPR, and in the nation's leading newspapers, magazines, and websites. Do you have a nutrition question? Call the Nutrition Diva listener line at 443-961-6206. Your question could be featured on the show.