Over the past decade, increasing amounts of research are tying higher vitamin K intakes to lower risks of insulin resistance, metabolic syndrome, diabetes, and related cardiovascular diseases. Mainstream recommendations coming out of the Institute of Medicine for vitamin K claim that 120 mcg (micrograms) per day for adult men and 90 mcg for adult women is “adequate intake”. But research increasingly indicates this is not enough to get the full benefits of vitamin K. Additionally, there is no adequate intake recommendation specifically for the distinct K1 and K2 forms even though both are clearly important in different ways.
Generally an intake of somewhere above 50 mcg per day of vitamin K1 is viewed as enough to support blood clotting functions. Without that minimal amount of vitamin K, the body cannot create enough clotting proteins necessary to stop bleeding normally. In fact very low levels of vitamin K can even produce abnormal bleeding even without any obvious injury, as was shown by early vitamin K researchers who showed they could cause internal bleeding in chickens by depriving them of vitamin K. However, the level of intake adequate to stop abnormal bleeding is insufficient to preserve or improve health in other areas such as brain, bone, and cardiovascular health. Additionally, for those health effects the vitamin K2 form is far more important, especially since the human body is not good at converting K1 to K2.
A Dutch study of 38,094 participants found that vitamin K1 intake is far greater than K2 and that higher intakes of vitamin K1 and K2 were both connected to lower rates of diabetes. Higher K2 intake was also linked to improved blood lipids and lower C-reactive protein, both common markers for cardiovascular health.
Vitamin K1 intake among the study participants averaged 200 micrograms per day and vitamin K2 intake averaged 31 micrograms per day. Over a median follow-up period of 10.3 years, 918 cases of type 2 diabetes were diagnosed. Adjusted analysis of the data uncovered a 19 percent lower risk of developing diabetes in men and women whose vitamin K1 intake was among the highest 25 percent of subjects compared with those whose intake was among the lowest fourth.
A linear inverse relationship was observed between vitamin K2 and the development of diabetes. For each 10 microgram increment increase in intake, a 7 percent reduction in risk was noted. Greater consumption of vitamin K2 was also associated with improved blood lipids and reduced levels of C-reactive protein, a marker of inflammation.
However, in the US the typical American adult gets far less vitamin K1 than those in the Dutch study. Researchers from Tufts University estimated in 1996 that the average American adult only gets around 59 to 82 mcg per day of vitamin K1.
Vitamin K Can Help Insulin Work Better
A Tufts University study of 355 men and women ages 60 to 80 published in 2008 looked at how vitamin K supplementation slowed the development of insulin resistance associated with metabolic syndrome and diabetes. This study used 500 mcg (micrograms) per day of vitamin K1 supplementation, the form most common in plant food products such as vegetables.
The authors reported that the supplements helped men’s bodies use insulin more effectively but did not not appear to help women.
“Men who received vitamin K supplementation had less progression in their insulin resistance by the end of the clinical trial,” said Sarah L. Booth, PhD, senior author and director of the Vitamin K Laboratory at the USDA HNRCA. “Conversely, we saw progression in insulin resistance in women who received vitamin K supplementation, and in the men or women who were not given vitamin K supplements.”
The researchers speculate the vitamin K supplements may not have helped the women in the study because they had a higher rate of obesity and high body weight. It is possible that vitamin K at 500 mcg (micrograms) per day may not be adequate to overcome the metabolic effects of obesity.
Vitamin K2 Has Distinct Benefits
Researchers suspect that pharmacological grade vitamin K1 supplements beyond 1000 mcg (or 1 mg) per day probably won’t be absorbed well by the human digestive tract. Vitamin K2, however, can be absorbed at much higher levels. Japanese doctors have been using 45 mg of vitamin K2 per day, generally three doses of 15 mg each, to treat osteoporosis for more than a decade.
Vitamin K2 is known to be more concentrated in certain areas in the human body including the brain, salivary glands, and pancreas which is the organ that produces insulin. Researchers believe that the human body is able to inefficiently convert K1 to K2 in small quantities. Thus it is possible that supplementation with vitamin K2 could produce a different, quite possibly superior, effect than seen with K1.
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Most vitamin K2 research has focused on effects involving osteoporosis and arterial calcification where it has been shown to be very helpful. Unfortunately, K2’s other uses in the body are mostly unexplored.
The pancreas has the second highest amount of vitamin K in the body. This suggests the vitamin may have something to do with controlling blood sugar. In the first study of its kind, researchers in Japan looked at vitamin K’s effect on glucose and insulin. In a study on rats, they found that vitamin K deficiency initially impedes the clearance of glucose, then causes too much insulin to be released. This can be plotted on a graph that looks very similar to what occurs in diabetes.
K2 is the dominant form of vitamin K in the pancreas, suggesting that supplementing directly with K2 may be more beneficial than supplementing with K1 and hoping that some if it is converted to K2.
Korean researchers demonstrated that vitamin K2 supplementation could also significantly increase insulin sensitivity, but this time in healthy young men in a placebo-controlled study. They suspect that the added K2 allows more osteocalcin to become carboxylated (which activates it for use) and this improves insulin sensitivity.
Other researchers have found that mitochondria, the energy producing power plants of cells, have special uses for vitamin K2 that improves energy production. As mitochondria can “burn” various fuel sources, this may also have something to do with observations of improved insulin sensitivity and blood lipid profiles.
Basic research into the effects of vitamin K2 in the brain have found that it protects a number of cell types from damage that may be involved in neurological diseases such as Alzheimer’s, Parkinson’s, and multiple sclerosis (MS).
Measuring Your Vitamin K
Unlike many vitamins, blood tests for directly measuring vitamin K variants are not widely available. Additionally, even if they were available, they may fail to measure K2 well because vitamin K2 is rapidly absorbed by tissues that need it and disappears from the blood often in a matter of hours. This is especially evident for the K2 MK-4 (also known as menaquinone-4 and menatetrenone) form that seems to be widely used in the body.
You may be able to estimate if you are getting enough vitamin K and how diet and supplement changes are affecting your vitamin K status via tests usually used to monitoring bleeding and bone functions. Prothrombin Time (PT) tests can estimate how fast your blood clots. Insufficient levels of vitamin K generally produce longer clotting times. Osteocalcin blood tests are one of the more practical ways to determine vitamin K sufficiency in humans as this test is relatively common and inexpensive. These tests measure carboxylated osteocalcin which is connected to maintenance of the bones. Carboxylation of osteocalcin requires vitamin K, therefore low levels of osteocalcin may be caused by inadequate vitamin K intake.
The Prothrombin Time test probably reflects vitamin K1 more than K2 and the osteocalcin test K2 more than K1. As most people get enough K1 for maintaining normal coagulation but may not get enough K2 to maximize bone maintenance functions, the osteocalcin test is probably more useful for judging overall vitamin K status.
Increasing Your Vitamin K
Increasing vitamin K intake by diet and supplements is safe for most people. The main exception is those taking dangerous vitamin K antagonist drugs such as warfarin for controlling their coagulation. These drugs interfere with the action of vitamin K in the body, thus slowing blood clotting but also unfortunately damaging bone maintenance and vitamin K protective functions in the brain and likely other organs such as the pancreas and the salivary glands. K2 function in the salivary glands is particularly interesting as it appears to be connected to remineralization processes that allow saliva to repair weak or damaged tooth surfaces. This is thought to explain why dentist Weston Price observed that populations that have diets poor in vitamin K (particularly the at-the-time unknown vitamin K2 which he called “Activator X”) tend to have more dental cavities.
For the most part, mainstream diet and nutrition discussion focuses almost exclusively on vitamin K1 that you find primarily in plant based foods. However, studies show humans have trouble absorbing more than 200 mcg of vitamin K1 from diet or more than 1000 mcg from supplements per day and K1 to K2 conversion is not very efficient. So you should be looking for foods and supplements that offer vitamin K2, particularly the MK-4 and probably also the MK-7 (also known as menaquinone-7) forms that are the most researched so far. Paleolithic diet advocates would have you getting these largely from animal meats and organs such as liver. Cheese, diary products and eggs may also be good sources particularly if they are from grass-fed animals. Grain-fed cows and chickens have clearly lower vitamin K levels. Natto (a type of Japanese fermented soy) is one of the few vegetarian-friendly sources for K2, but the taste is certainly not widely appealing.
Many paleo diet bloggers and writers covering dentist Weston Price’s nutritional research on the prevention of dental diseases are advocates of butter oil products such as ”Green Pastures X-Factor Gold High-vitamin Butter Oil” as sources of vitamin K2. However, few if any of these products have much consistency in their levels of vitamin K2. For example, you should expect that butter oil made from milk produced while cows are eating rapidly growing grasses will have K2 that is much higher than that made during the winter. There also seem to be supply constraints with some of these products. While these products certainly could help raise your vitamin K intake, the effect will vary from batch to batch and if you can’t get them due to supply problems than this of course is of no help.
I’d advocate doing what you can to improve your diet to include dietary quality vitamin K1 and K2 sources such as K1 and K2 rich foods (and possibly butter oil if you like it and can afford it) while also ensuring you get at least a reasonable minimum amount each day via a supplement with a known quantity of K1 and K2 forms.
Boosting vitamin K1 intake is relatively easy by simply eating more leafy green vegetables such as kale, broccoli, chard, parsley, spinach, and lettuces. Kale is a really magnificent source of vitamin K1, whereas light green lettuces such as iceberg are not nearly so good but still better than most breads and cereals.
Boosting vitamin K2 intake generally requires consuming foods produced from animals or bacterial fermentation such as cheeses, organ meats such as liver, eggs (particularly the yolks), and fermented soybeans such as natto. Animals that are fed vitamin K rich diets, such as free-ranging pasture fed cows, are likely to have much higher levels of vitamin K and therefore foods made from their milk or meat are also going to be higher in vitamin K.
Animals based foods that have not been fermented or aged tend to have more of the K2 MK-4 form that is used very rapidly by the body. Fermented or aged foods tend to have higher levels of the K2 MK-7 form that tends to last more than a day in blood circulation. It is not clear from today’s research which is the superior form, but MK-4 is certainly less expensive in supplement form than MK-7. Consuming supplements containing both forms is probably a good idea, but for cost reasons large amounts of K2 MK-4 and smaller amounts of MK-7 are more practical than the reverse.
The Life Extension Super Booster with Advanced K2 Complex product is a reasonably good choice as it offers 1000 mcg of K1, 1000 mcg of K2 MK-4, and 100 mcg of K2 MK-7 along with other useful nutrients such as mixed tocopherol vitamin E. If you want to focus just on the vitamin K, they also have a product Super K with Advanced K2 Complex which leaves out most of the other nutrients and bumps the number of softgels per bottle from 60 to 90.
If you’re looking for higher levels of K2 MK-4 as supplements such as might be used to help with osteoporosis or arterial calcification or to boost insulin sensitivity, 15 mg capsules are currently the largest ones I was able to find. Vitamin Research Products Ultra K2 is such a product and uses a very tiny capsule that is easy to swallow. Japanese studies of up to 45 mg per day (three doses of 15 mg each) show it is safe for most people, the main exceptions being those on warfarin as mentioned previously. There is also an intermediate dosage product ”Carlson Labs Vitamin K2 5 mg” that offer twice the number of capsules for about the same price, making it more affordable to take the rapidly utilized MK-4 with each meal.
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