For those without any complicating factors, what’s the case for high-dose K2 supplementation?
Vitamin K2 plays an important role in heart health and bone formation. But how much is enough, and is it safe to take high doses?
Nutrition Diva is hosted by Monica Reinagel. A transcript is available at Simplecast.
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Hello, I’m Monica Reinagel and this is the Nutrition Diva podcast, a show where I take a closer look at nutrition trends and headlines, explain what the latest research means for you, and answer your nutrition questions. Welcome.
Judy writes: “Can you discuss the importance of K2 in maintaining and building strong bones as we age? I have been taking 45 mcg a day but have heard that we should be taking 45,000 mcg daily.”
That’s not an insignificant difference, so I can understand your confusion! But before we get into the question of mega-dosing, let’s back up and lay some groundwork.
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 #25, Diet for Healthy Bones) as well as heart health.
The Institute of Medicine has not yet established a Recommended Daily Allowance for vitamin K. This happens when they feel they don’t have enough evidence to say for sure how much is needed to meet the needs of healthy individuals. Instead, they have set an Adequate Intake of 90 mcg for women and 120 mcg for men. Adequate Intakes are based on how much of a nutrient most people seem to be getting. The primary dietary sources of vitamin K are spinach and other leafy greens, broccoli and other cruciferous vegetables, and oils, particularly soybean and canola oil.
Dietary surveys suggest that the average daily vitamin K intake from foods is 120 mcg for adult women and 140 mcg for men. If we count both foods and supplements, average daily intake increases to 160 mcg for women and 180 mcg for men. In other words, vitamin K deficiency is rare. But there’s often a distinction to be made between sufficient intake of a nutrient (enough to prevent deficiency) and optimal intake, which might provide additional benefits. The Dietary Reference Intakes (RDAs and AIs) are really focused more on preventing disease of deficiency than promoting optimal health outcomes.
Vitamin K is actually a family of closely related compounds. Vitamin K1, also known as phylloquinone, is the form that's found in vegetables and oils. Many of the vegetables that are high in vitamin K are also high in calcium. Perhaps that explains this mystery: researchers noticed that people whose diets are particularly high in vitamin K have a much lower incidence of bone fractures as they get older than people whose diets are low in vitamin K. “A-ha!” they thought. “Vitamin K prevents osteoporosis.”
Later, scientists were disappointed to find that taking vitamin K supplements had no effect on fracture risk. But the folks that they had originally observed, who seemed to have stronger bones, weren’t taking vitamin K supplements. They were eating foods rich in vitamin K. It just so happens that these foods are also rich in calcium, magnesium, and other bone-building nutrients. In other words, single nutrients generally don’t prevent bone loss. But a nutrient-rich diet does.
The other primary form of this nutrient, 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. If you take a vitamin K supplement, it’s likely to be the K2 form. But before we talk about K2 supplements and how much you should be taking, let’s talk about natural sources.
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.
Natto is made from fermented soybeans. Although it's a daily staple for many Japanese, most Westerners have never heard of it, much less tried it. Like many fermented foods, natto has a somewhat strong flavor and aroma. Some might even describe it as "funky." Let's just call it an acquired taste.
If you want to try it, I suggest first preparing it in the traditional Japanese way. Here's how a friend who grew up with a Japanese mom once made it for me:
Whisk together 1 raw egg, 4 tablespoons low sodium soy sauce, 1 teaspoon sesame oil, 1 teaspoon prepared mustard or wasabi, and 1 finely chopped green onion. Combine natto with the sauce mixture and spoon over hot white rice. The result is a flavorful, savory dish that you can enjoy as a light lunch, snack, or appetizer.
In addition to being a potent source of vitamin K2, natto is also a good source of protein, fiber, and isoflavones.
You can vary the proportions of soy sauce, sesame, and mustard to suit your taste. Although the raw egg is traditional (and does a lot to mellow the flavor of the raw natto), you can omit this if you have any concerns about eating raw eggs—or use eggs that have been pasteurized in the shell.
You'll find natto at Asian grocers or health food stores. It's usually sold frozen or in vacuum-sealed pouches. If you can't find it locally, there are several online Japanese and Asian grocers who can ship it to you. Natto is very inexpensive, about $1 per serving. Serious do-it-yourself-ers can even make natto at home, using dried soybeans and natto spores. Natto spores and instructions are available from www.culturesforhealth.com
With that, let’s now turn to Judy’s question about dosage for vitamin K2 supplements and whether very high doses are safe and effective.
In general, vitamin K is thought to be quite safe, even in very high amounts. The Institute of Medicine has not set a Tolerable Upper Limit for this nutrient. And it has been widely used at very high doses to treat or prevent osteoporosis, particularly in Japan.
That said, there are a few people who should not take vitamin K at all. Vitamin K will interfere with the medication coumadin (Warfarin), which is a drug used to prevent blood clots. So these should not be combined. In fact, people who take coumadin need to be mindful of their intake of those foods that are high in vitamin K, such as broccoli. They don’t necessarily need to avoid these foods—which are otherwise quite healthful and nutritious. But they need to keep their dietary intake of vitamin K consistent so that their medication can be correctly calibrated to their typical intake.
And if you have any sort of clotting disorder, you’d also want to be extremely careful with vitamin K supplements. This is definitely a check with the doctor situation.
However, for those without any complicating factors, what’s the case for high-dose K2 supplementation?
As I mentioned earlier, high-dose vitamin K2 has been used in Japan as a prescription medication to treat and prevent bone loss. And there have been a couple of studies using 45,000 mcg (aka 45 mg) of vitamin K2. One of these studies tested a 45-mg dose of K2 in women with osteoporosis and found that it helped the women maintain bone density over time and reduced the incidence of fractures by about half. The other study compared high-dose K2 to an osteoporosis drug and found that K2 was not quite as effective in maintaining bone density. However, it reduced the risk of spinal fractures to a similar extent as the osteoporosis medication, with fewer side effects.
One big limitation of these studies is that all of the subjects were post-menopausal Japanese women with osteoporosis. We’d want to repeat similar experiments in other populations (such as Western women or women who do not yet have osteoporosis) to see whether the effects are similar when some of the variables have changed.
At this point, I would characterize the research on high-dose K2 as a treatment or preventive for osteoporosis as promising but preliminary. Normally, when talking about prescription medications, my next bit of advice would be to talk with your doctor to see what she thinks about whether high-dose K2 might make sense for your situation.
However, here in the U.S., you do not need a prescription for a high-dose K2 supplement. And vitamin sellers offering high-dose K2 are quick to cite these two studies in their “educational” literature. They can’t include this information in their marketing materials, because it is illegal to suggest that a dietary supplement can treat, prevent, or cure a specific disease. But the line between educational materials and marketing is mostly a regulatory dance. Suffice it to say that vitamin sellers are very good at getting the information out there. They’re also very good at spinning the story.
Because K2 seems to be quite safe, the main danger of over-hyping high-dose K2 for osteoporosis would seem to be spending a bunch of money on something that doesn’t do much good. If you or your doctor is concerned about your risk of bone fractures or developing osteoporosis, you could certainly share this information with her and talk about whether a K2 supplement makes sense and how much you should consider taking.
But if you’re just interested in doing what you can to maintain strong, healthy bones as you age, remember that there are lots of nutrients involved in bone health. It’s not just about calcium, vitamin D or vitamin K. It’s also about magnesium and boron and so many others. Even protein plays a role. As with so many other things, your best bet is a varied diet with lots of nutrient-rich foods.
Thanks, Judy for your question. If you have a question you'd like me to answer, you can email me at nutrition@quickanddirtytips.com You can also leave me a message at 443-961-6206. As you can see—your question stands an excellent chance of being featured in an upcoming episode.
I’d also like to invite you to check out my other podcast. It’s called the Change Academy, where we explore the art and science of creating positive behavior change, both in our own lives and in our workplaces and communities. You can find it on all the major podcast platforms. Just search for Change Academy.