If there was a vitamin that could help you maintain bone strength, improve cardiovascular health, and perhaps protect brain function, wouldn’t you want to know about it? For many decades, vitamin K was thought to be required only for blood coagulation, but a separate form of vitamin K—K2—has roles in bone, heart, and perhaps, brain health.
First, Some Background:
Vitamin K was discovered around 1930 by a Danish chemist and because it was intrinsic to blood clotting, the K referenced “koagulation.” Vitamin K has two natural forms: K1 (phylloquinone) and K2 (menaquinone) with menaquinone abbreviated as MK. (Why MQ wasn’t used is beyond me.)
Menaquinones have a side chain, and without going into more chemistry, their subtype numbers reflect the chain’s length. The most studied menaquinones are MK-4, MK-7, and MK-9[1] and ongoing research is revealing how these impact calcium distribution in the body to increase bone mineral content and reduce calcifications in the heart and blood vessels.[2] There are also credible suggestions that Vitamin K2 may reduce inflammation within the brain.
Vitamin K Functions in the Body:
While both forms of vitamin K aid in activating coagulation proteins made by the liver, vitamin K2 has additional effects on several other Vitamin K-Dependent Proteins (VKDPs) found outside the liver.
Coagulation:
Blood clotting requires both adequate numbers of platelets (the potentially sticky cell fragments in the blood) and effective coagulation, which is achieved after several proteins are activated in quick succession after an injury. Vitamin K (both 1 and 2) is needed for coagulation; thus, a vitamin K deficiency could lead to bleeding and bruising tendencies.
Bone Health:
Vitamin K2 aids in activating the VKDP, osteocalcin, for bone formation in both children and adults. In childhood and adolescence, bone growth, or modeling, leads to increased stature. In adulthood, bone remodeling provides maintenance and structural changes which are dependent on posture, activity or lack thereof, injuries, age, hormonal influences, drug effects, and calcium needs in the body elsewhere.[3]
Osteopenia is the loss of bone mass due to reduced hormone support (e.g., estrogen), inactivity, smoking, drug side effects, certain medical conditions, and inadequate intake of calcium, vitamin D intake, and perhaps vitamin K2. Advancing osteopenia may progress to osteoporosis resulting in diminished bone strength, reduced height, and increased risk of fractures.
Research on vitamin K2 is promising. A study of MK-7, in conjunction with Vitamin D and calcium, showed a reduction in the loss of calcium from the lower spine vertebral bones in postmenopausal women receiving 180 mcg/day of MK-7.[4] Another examination of menaquinones showed improved bone strength and bone mineral content in postmenopausal women taking 45 mcg/day over 3 years.[5]
Cardiovascular Health:
While vitamin K2 promotes calcium accumulation in bone, it prevents calcium deposition in the cardiovascular system by assisting activation of another VDKP, matrix Gla protein. Research suggests that menaquinone deficiency is associated with calcifications within blood vessels and the heart, including the coronary arteries, aorta, and both mitral and aortic valves.[6]
But what about adding vitamin K2 to the diet? Two studies using postmenopausal women described positive effects of menaquinones by showing reduced arterial stiffness[7] or a trend toward decreased calcification of coronary arteries.[8] Another investigation on women over several years showed that vitamin K2 appeared to reduce coronary heart disease incidence.[9]
Limitations on the first two investigations include small sample sizes (244 and 564, respectively) and in the latter two, the use of a questionnaire to determine Vitamin K dietary intake rather than using a measured dose by pill. Further investigations are needed.
Brain Health:
The VKDP, Gas6 protein, appears to modulate inflammation, especially in the brain where this protein is plentiful. Studies suggest that it may be protective against beta-amyloid, a substance that is harmful to brain cells and is associated with Alzheimer’s disease.[10] Prevention of neuroinflammation, lessening the accumulation of beta-amyloid, and improvement of cardiovascular health all reduce the risk of dementia. Further research can’t come soon enough.
Vitamin K Sources & Requirements:
Food is the primary source of Vitamin K although the body can make some MK-4 from phylloquinone.[11] Vitamin K is also recycled to some extent by the body.[12]
While most people can safely include more Vitamin K-containing foods in their diet, patients taking warfarin (a “blood thinner” AKA CoumadinÒ and others) are advised to avoid these foods.
Dietary Sources of Vitamin K1:
Vitamin K is found in the greatest amounts in green leafy vegetables (such as kale, collard, and turnip greens, spinach, broccoli, lettuces, and algae like kelp), but also in fruits (especially prunes, kiwifruit, and avocado), nuts (pine nuts and cashews)[13] and liquid vegetable oils, especially olive, soybean, and canola oils.[14] Consuming meals with fats and oils improves absorption of this fat-soluble vitamin. Unfortunately, high heat frying transforms phylloquinone in the oil into a hydrogenated form that has questionable effectiveness in vitamin K functions.[15]
Dietary Sources of Vitamin K2:
MK-4, comes from animal products, the best source being goose meat and its liver. Egg yolks, chicken, and some fatty luncheon meats provide decent amounts with leaner meats and milk supplying lesser quantities.[16]
MK-7, is found in bacterially fermented plant products. Natto, a Japanese soybean product, is a superfood with its stellar MK-7 content;[17] however, it is described as an acquired taste. MK-7 is also present in sauerkraut and perhaps kimchi, miso, and kombucha.
MK-9, comes primarily from bacterially fermented dairy products: buttermilk, yogurt, and cheeses (hard, soft, and curd).[18]
Vitamin K Requirements:
The current Recommended Daily Intake (RDI) of vitamin K is 120 mcg for men and 90 mcg for women, but there is currently no breakdown regarding K1 vs K2 needs. So, one must take stock of one’s food choices and dietary habits.
Low fat diets prohibit some foods rich in vitamin K2 and can reduce its absorption. Not only that, but eggs and cheese got a bad rap regarding cholesterol so many gave them up. In the past, fermentation was important to preserve food, but now, for many, fermented products are not to their taste. “Fast foods” often are cooked with high heat which can reduce the amount of active vitamin K1.
Even if you eat a healthy balanced diet, you may decide to change a few things: eat more greens, add a few fermented items to your menu, consume more cheese, make oil choices based on their vitamin K content, and even try natto. (Anything to avoid taking another pill.)
Others want to make sure their basic needs are being met and will buy a vitamin K2 supplement (usually MK-7). In that case, a bottle with the USP designation on the label guarantees consistent dosing at the level promised and that no contaminants are present. Taking the supplement with a meal containing fats also helps. Vitamin K2 is not low-priced so you might take it every other day.
While no toxicity or serious side effects have been demonstrated with high doses of menaquinone, I would err on the side of keeping the dose below 180 mcg/day.[19] Certainly, you should ask your physician if this product is safe for you to take, especially if you are on other medications like blood thinners.
[1] Quanxiang Yan et al., “The Biological Responses of Vitamin K2: A Comprehensive Review,” Food Science & Nutrition 11, no. 4 (January 6, 2023): 1634–56, https://doi.org/10.1002/fsn3.3213.
[2] Domitilla Mandatori et al., “The Dual Role of Vitamin K2 in ‘Bone-Vascular Crosstalk’: Opposite Effects on Bone Loss and Vascular Calcification,” Nutrients 13, no. 4 (April 2021): 1222, https://doi.org/10.3390/nu13041222.
[3] Vamsee D. Myneni and Eva Mezey, “REGULATION OF BONE REMODELING BY VITAMIN K2,” Oral Diseases 23, no. 8 (November 2017): 1021–28, https://doi.org/10.1111/odi.12624.
[4] M. H. J. Knapen et al., “Three-Year Low-Dose Menaquinone-7 Supplementation Helps Decrease Bone Loss in Healthy Postmenopausal Women,” Osteoporosis International: A Journal Established as Result of Cooperation between the European Foundation for Osteoporosis and the National Osteoporosis Foundation of the USA 24, no. 9 (September 2013): 2499–2507, https://doi.org/10.1007/s00198-013-2325-6.
[5] M. H. J. Knapen, L. J. Schurgers, and C. Vermeer, “Vitamin K2 Supplementation Improves Hip Bone Geometry and Bone Strength Indices in Postmenopausal Women,” Osteoporosis International: A Journal Established as Result of Cooperation between the European Foundation for Osteoporosis and the National Osteoporosis Foundation of the USA 18, no. 7 (July 2007): 963–72, https://doi.org/10.1007/s00198-007-0337-9.
[6] Essa Hariri et al., “Vitamin K2—a Neglected Player in Cardiovascular Health: A Narrative Review,” Open Heart 8, no. 2 (November 16, 2021): e001715, https://doi.org/10.1136/openhrt-2021-001715.
[7] Marjo H. J. Knapen et al., “Menaquinone-7 Supplementation Improves Arterial Stiffness in Healthy Postmenopausal Women. A Double-Blind Randomised Clinical Trial,” Thrombosis and Haemostasis 113, no. 5 (May 2015): 1135–44, https://doi.org/10.1160/TH14-08-0675.
[8] Joline W. J. Beulens et al., “High Dietary Menaquinone Intake Is Associated with Reduced Coronary Calcification,” Atherosclerosis 203, no. 2 (April 2009): 489–93, https://doi.org/10.1016/j.atherosclerosis.2008.07.010.
[9] G. C. M. Gast et al., “A High Menaquinone Intake Reduces the Incidence of Coronary Heart Disease,” Nutrition, Metabolism, and Cardiovascular Diseases: NMCD 19, no. 7 (September 2009): 504–10, https://doi.org/10.1016/j.numecd.2008.10.004.
[10] Alexander Popescu and Monica German, “Vitamin K2 Holds Promise for Alzheimer’s Prevention and Treatment,” Nutrients 13, no. 7 (June 27, 2021): 2206, https://doi.org/10.3390/nu13072206.
[11] Leon Schurgers and Cees Vermeer, “Determination of Phylloquinone and Menaquinones in Food. Effect of Food Matrix on Circulating Vitamin K Concentrations,” Haemostasis 30 (November 1, 2000): 298–307.
[12] Yan et al., “The Biological Responses of Vitamin K2.”
[13] Asim Cengiz Akbulut et al., “Vitamin K2 Needs an RDI Separate from Vitamin K1,” Nutrients 12, no. 6 (June 21, 2020): 1852, https://doi.org/10.3390/nu12061852.
[14] Sarah L. Booth, “Vitamin K: Food Composition and Dietary Intakes,” Food & Nutrition Research 56 (April 2, 2012): 10.3402/fnr.v56i0.5505, https://doi.org/10.3402/fnr.v56i0.5505.
[15] Sonya J. Elder et al., “Vitamin K Contents of Meat, Dairy, and Fast Food in the U.S. Diet,” Journal of Agricultural and Food Chemistry 54, no. 2 (January 1, 2006): 463–67, https://doi.org/10.1021/jf052400h.
[16] Schurgers and Vermeer, “Determination of Phylloquinone and Menaquinones in Food. Effect of Food Matrix on Circulating Vitamin K Concentrations.”
[17] Booth, “Vitamin K.”
[18] Schurgers and Vermeer, “Determination of Phylloquinone and Menaquinones in Food. Effect of Food Matrix on Circulating Vitamin K Concentrations.”
[19] Akbulut et al., “Vitamin K2 Needs an RDI Separate from Vitamin K1.”
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