Friday Favorites: Vitamin K2’s Purported Benefits - Should You Take Supplements?

Vitamin K. Wait, I know about vitamins A, B, C, D, and E. What happened to vitamins F, G, H, I, and J? It's not alphabetical. Vitamin K stands for coagulation, or at least it does in German. That's the fundamental role vitamin K plays, helping the blood to clot. But over the last few decades, there's evidence that it has other roles in the health of our bones, heart, and brain. Kind of reminds me of vitamin D. I mean, we know vitamin D is important for bone health, but then there have been all sorts of other controversial functions ascribed to it, some of which have been proven and some disproven. What about vitamin K? For bone health, for example, is the link between vitamin K and osteoporosis myth or reality? It turns out the findings on vitamin K in bone are conflicting and unclear. It doesn't help that some of the major trials were found to be problematic, to say the least, as in likely fraudulent, containing impossible data, with investigators admitting to complete fabrication. And so, if you do a systematic review eliminating any fraud, we find there's no evidence that vitamin K supplementation affects bone mineral density or vertebral fractures. What about the heart? Vitamin K supplementation for the prevention of cardiovascular disease. There's a vitamin K-activated protein in your blood that binds up excess calcium and helps prevent calcium from being deposited into the walls of your arteries and stiffening them. So if you give people extra vitamin K, will that protect people's arteries from calcification? It sounds good in theory, but no, vitamin K does not appear to consistently prevent progression of calcification, atherosclerosis, or arterial stiffness. For example, artery calcification is particularly common in patients with chronic kidney disease, which can lead to increased artery stiffness, which is an important risk factor for heart attacks and strokes. An earlier trial didn't find any benefit on coronary artery calcification between the vitamin K and placebo groups, but they were using kind of a small dose. So these trials used a whopping dose daily for a year, and nada. Vitamin K supplementation did not improve vascular stiffness or other measures of artery health. In fact, one study on the effect of vitamin K supplementation on artery calcification in patients with diabetes found that calcification tended to increase after supplementation with a type of vitamin K found in a slimy fermented soy food called natto. Now, those with higher levels of vitamin K circulating in their bloodstreams do tend to have lower levels of inflammation, but no wonder. Where is vitamin K found? The predominant dietary form of vitamin K in the human diet comes from dark green leafy vegetables and cruciferous vegetables. So how did people get high levels in their blood? Eating broccoli. Those with higher levels of vitamin K in their blood were eating more vegetables, less meat, no wonder they had lower levels of inflammation. The recommended adequate daily intake for vitamin K is set at 70 micrograms a day in Europe and between 90 and 120 a day here in the United States. Just two leaves of kale has over 70, and a quarter cup of cooked kale will get anyone all the K they need for the day. Now, there is vitamin K found in meat, dairy, and eggs, averaging about 5 to 10 micrograms per serving. In other words, they are even beaten out by iceberg lettuce, which is mostly water, but still contains like 2 to 3 times more vitamin K. Ah, but that's vitamin K1. What's found in animal products is mostly vitamin K2. Do you need K2? Apparently not. Once you get enough plant-based K1, there's no established requirement for K2, because it hasn't been proven that K2 has effects that are different from K1. They both act the same way in the body, thus there's not even enough data to take K2 into account at all. So when the recommended adequate daily intakes are set, they're only talking about getting enough K1 from plants, mostly green vegetables. In fact, most of the bone trials that flopped used the K2 found in animal products, and most of the failed heart studies used K2 as well. OK, even though there's presently a lack of randomized trial evidence to support a beneficial role for vitamin K in preventing the worsening of cardiovascular disease or bone health. What if that were to change? What if, all of a sudden, K2 was shown to have unique benefits? Well, guess what? The bacteria in your gut make K2. That's why fermented foods have K2. Bacteria make it. And the bacteria in your gut not only make it, but it gets absorbed from your colon up into your system, contributing a significant amount of the human vitamin K requirement, just in case you miss a couple days of greens. Vitamin K1 is made by plants and is the primary dietary form. Then there are a dozen or so types of vitamin K2, which are synthesized by bacteria, including several types in the human gut. The exception, though, is a type of K2 called menaquinone 4, MK4, which is endogenously synthesized in mammals and therefore is found in animal products. Now, I don't know if any of you noticed, but were mammals too? It has consistently been shown that vitamin K1 from greens is endogenously converted inside your body to the vitamin K2 in animal products. You're made out of meat, too, though it took until 2010 before we discovered the human biosynthetic enzyme that does it. So, no reason at all to take any sort of vitamin K supplement. Eat your greens. In fact, when K2 supplements were looked at, researchers found significant problems in terms of contaminants and mislabeling. Eat your greens. Now, K2 appears in higher concentrations in certain tissues, including the brain. Again, we make K2 from the K1 we eat in greens, but maybe extra K2 might help. Well, if you measure vitamin K levels in the blood and brains of centenarians, those that live over 100, concentrations of circulating K1 from vegetables, but not cerebral K2, not the K2 in the brain, was positively correlated with a wide range of cognitive measures. Why? Likely because they were eating green vegetables. And green vegetables don't just have vitamin K. Green leafy vegetables are the most concentrated source of lutein, the eye health nutrient that's taken up into the brain and is associated with cognitive performance across the lifespan. And so in the centenarians, circulating K1 and lutein concentrations were highly correlated, so it's hard to tease out exactly what in greens was so beneficial. It's like when you see data showing lower circulating K1 levels in the bloodstream are associated with the increased risk of all-cause mortality, meaning lower K1 levels were correlated with a shorter lifespan. Well, duh! K1 is found in greens, and of all the dietary components correlated with all-cause mortality, the best evidence appears to support the intake of green leafy vegetables and salads to reduce all-cause mortality. In other words, eat your greens.