June 2013 Issue
Vitamin K2 — A Little-Known Nutrient Can Make a Big Difference in Heart and Bone Health
By Aglaée Jacob, MS, RD, CDE
Vol. 15 No. 6 P. 54
Ever since vitamin K was discovered in the early 1930s, all the attention has been directed toward its role in coagulation. Although both the K1 (phylloquinone) and K2 (menaquinone) forms of the vitamin were identified at that time, they were thought to be simple structural variations. It’s only in the 21st century that the distinct nature of vitamin K2 was finally recognized.
Vitamin K1 deficiency is rare and almost nonexistent, unlike vitamin K2 deficiency.1 Because of the possibility of vitamin K2 deficiency, it’s important for RDs to be aware of this little-known nutrient and the beneficial impact it can have on their clients’ and patients’ heart and bone health.
Optimizing bone health isn’t as simple as getting enough dietary calcium. Beyond the obvious importance of this mineral, other factors, such as vitamin D and magnesium intake, low-grade systemic inflammation, weight-bearing exercise, and intestinal health, also impact bone mineral density, and vitamin K2 should be added to the list.
This fat-soluble vitamin is required to activate osteocalcin, an important protein secreted by osteoblasts, the body’s bone-building cells. When vitamin K2 is activated, osteocalcin can draw calcium into the bones where osteoblasts then incorporate it into the bone matrix.2 In addition, vitamin K2, when combined with vitamin D3, helps inhibit osteoclasts, the cells responsible for bone resorption.3
According to a recent study, the incidence of hip fractures in Japanese women seemed to be strongly influenced by their vitamin K2 intake. In Tokyo, the regular consumption of natto, a fermented soy food high in vitamin K2, is associated with a significantly lower risk of hip fractures compared with western Japan where natto isn’t frequently eaten.1 Studies examining the influence of vitamin D and vitamin K (including K1 and K2) intake in institutionalized elderly patients compared with home-dwellers also showed that a higher intake of these nutrients reduced bone fractures.1
Since 1995, high doses of vitamin K2 supplements have become an approved treatment for osteoporosis in Japan where studies support its benefit in the prevention of further decline in bone mineral density. Some women have experienced an increase in bone mass as a result of this intervention.1 Although these results are promising, more studies are needed to confirm their applicability to other populations.
The same osteocalcin protein that vitamin K2 activates also triggers the activation of another protein called matrix gla protein (MGP), which is responsible for removing excess calcium that can accumulate in soft tissues such as arteries and veins.2 This role takes on significant importance considering that about 20% of atherosclerotic plaques are comprised of calcium, from the early to the more advanced stages of heart disease development.2
Vitamin K2-activated MGP is considered the strongest factor in preventing, and possibly even reversing, tissue calcification involved in atherosclerosis, as described in the October 2008 issue of Thrombosis and Haemostasis. Patients with diabetes have been shown to have lower MGP levels in their arteries, possibly contributing, at least partly, to the higher risk of arterial calcification and cardiovascular disease seen in this population.
Data from the Rotterdam Study, which followed more than 4,800 subjects aged 55 and older for up to 10 years, showed associations between vitamin K2 intake and aortic calcification. Subjects diagnosed with severe aortic calcification had a lower intake of vitamin K2 compared with subjects with mild to moderate aortic calcification.4
Calcium Supplementation With K2 Deficiency
Many physicians recommend calcium supplements to postmenopausal women to help prevent or treat osteoporosis. The question is whether they should, especially if postmenopausal women are deficient in vitamin K2, which may put them at risk of developing cardiovascular diseases. Calcium is the main mineral present in the bone matrix, but supplementing with it doesn’t necessarily result in stronger bones if it accumulates in veins and arteries instead of in bones.
Further study is needed to answer this question about the efficacy and safety of calcium supplementation if a postmenopausal woman is deficient in vitamin K2. But based on the current literature, calcium supplements probably shouldn’t be recommended. A large-scale meta-analysis published in the December 2007 issue of the American Journal of Clinical Nutrition found that calcium supplementation doesn’t lower the risk of hip fracture in men or women—in fact, it may increase it.
Results from a 2011 meta-analysis published in BMJ, which other researchers have replicated, showed that calcium supplementation with or without vitamin D significantly increased the risk of myocardial infarction or stroke in postmenopausal women. The data were taken from the Women’s Health Initiative that included a cohort of 36,282 women. The dietary calcium intake of the women averaged around 800 mg/day, while those supplementing with calcium obtained an additional 585 mg/day.5 Could their higher risk of cardiovascular diseases be caused by a deficient intake of vitamin K2? Additional study is needed to determine this and whether supplementing with vitamin K2 alone or in combination with calcium can produce better outcomes for bone and heart health.
Food Sources of Vitamin K2
In the meantime, it wouldn’t hurt to suggest that clients and patients eat foods rich in vitamins K1 and K2 for optimal health. While vitamin K1 mostly is found in leafy greens, animal products are the best food source of vitamin K2. The ideal way to obtain dietary vitamin K2 is to eat meat, especially organ meat (mainly liver), chicken, beef, bacon, and ham, according to data published in the January 2006 issue of the Journal of Agricultural and Food Chemistry. Egg yolks, but not egg whites, also provide valuable amounts of this fat-soluble nutrient as do high-fat dairy products, particularly hard cheeses made with whole milk.
Natto is the only vegetarian source of vitamin K2 because of a specific strain of bacteria used in its fermentation process. It should be noted that although intestinal bacterial synthesis is possible, it doesn’t appear to be sufficient in preventing vitamin K2 deficiency in most people.2
The reason we can get vitamin K2 from animal-derived foods is because animals have a unique ability to synthesize vitamin K2 from the vitamin K1 they obtain from grass. For this reason, meat, eggs, and dairy from pastured and grass-fed animals contain higher levels of vitamin K2 compared with their grain-fed counterparts.2
Many of the best food sources of vitamin K2 also are high in saturated fat, which has been accused of contributing to heart disease without adequate evidence to support this claim. A rigorous meta-analysis, including 347,747 subjects followed for up to 23 years, published in the January 2010 issue of the American Journal of Clinical Nutrition clearly showed that there’s a lack of significant evidence for blaming saturated fats for the development of coronary heart disease and cardiovascular diseases. Accordingly, subjects in the Rotterdam Study with the highest vitamin K2 intake consumed more total and saturated fats and also had lower total cholesterol values and higher levels of heart-protective HDL cholesterol.4 Therefore, RDs shouldn’t be afraid to recommend foods high in vitamin K2 despite their higher saturated fat content while monitoring their clients’ cardiovascular risk profile, especially if they emphasize high-quality, grass-fed and pastured animal sources.
Although serum vitamin K2 levels aren’t reliable, undercarboxylated osteocalcin represents an indirect marker for vitamin K2 status that should become more available in the future, providing a useful assessment tool for RDs and their clients and patients. Vitamin K2 supplementation also is available in the form of MK-4, a synthetic version produced from an extract of the plant Nicotiana tabacum, and MK-7, a more natural form sourced from natto, as alternatives to help clients meet their vitamin K2 requirements.
The current Dietary Reference Intake for vitamin K doesn’t differentiate between the types of this fat-soluble vitamin, but this hopefully will change with future revisions. In the meantime, knowing that food sources of vitamins K1 and K2 are different and that vitamin K2 deficiency is prevalent, RDs should look for ways to help their clients incorporate good sources of vitamin K2 into their diet to ensure proper calcium utilization in the body.
— Aglaée Jacob, MS, RD, CDE, is a freelance writer who specializes in diabetes education and digestive health, and currently is studying naturopathic medicine in Toronto.
1. Vermeer C, Shearer MJ, Zittermann A, et al. Beyond deficiency: potential benefits of increased intakes of vitamin K for bone and vascular health. Eur J Nutr. 2004;43(6):325-335.
2. Rheaume-Bleue K. Vitamin K2 and the Calcium Paradox: How a Little-Known Vitamin Could Save Your Life. 1st ed. Ontario, Canada; Wiley: 2011.
3. Plaza SM, Lamson DW. Vitamin K2 in bone metabolism and osteoporosis. Altern Med Rev. 2005;10(1):24-35.
4. Geleijnse JM, Vermeer C, Grobbee DE, et al. Dietary intake of menaquinone is associated with a reduced risk of coronary heart disease: the Rotterdam Study. J Nutr. 2004;134(11):3100-3105.
5. Bolland MJ, Grey A, Avenell A, Gamble GD, Reid IR. Calcium supplements with or without vitamin D and risk of cardiovascular events: reanalysis of the Women’s Health Initiative limited access dataset and meta-analysis. BMJ. 2011;342:d2040.
Comparison of Vitamins K1 and K2
Proper calcium utilization
Leafy greens and green vegetables
Liver, meat, egg yolks, high-fat dairy, and natto
90 to 120 mcg/day
Not yet determined