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.

Before 2006, there was little research distinguishing K1 from K2 in foods, but vitamin K2 plays important roles in your body —and you might not be getting enough.

On a nutrition label, vitamin K1 and vitamin K2 are both simply listed as vitamin K, even though your body treats them differently. Vitamin K1 and K2 share the same chemical ring structure but have varying side chain lengths. Vitamin K1, found in vegetables like leafy greens, has a monounsaturated tail with four carbon groups. Vitamin K2 forms have polyunsaturated tails with anywhere from four to 11 carbon groups and are called menaquinones, MK-4 through MK-11. MK-4 is found mostly from animal sources, while fermented vegetables are the main source of MK-7.

Vitamin K is a cofactor of the enzyme vitamin K carboxylase. In short, vitamin K helps add a carbon dioxide to a protein, giving it a negative charge and allowing it to bind to positively charged calcium. Vitamin K1 is preferentially used by the liver to activate blood-clotting proteins. The “K” originally stood for “koagulation.” Vitamin K2, on the other hand, is primarily used in other tissues to ensure that calcium is deposited where it should be, such as bone and cartilage, and to prevent calcium from accumulating where it shouldn’t, like blood vessels and kidneys.

Health Benefits of Vitamin K2

Bone Health

Optimizing bone health is not 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. In addition, when combined with vitamin D3, K2 helps inhibit osteoclasts, the cells responsible for bone resorption

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. Although these results are promising, more studies are needed to confirm their applicability to other populations.

Heart Health

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. 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.

Vitamin K2-activated MGP is considered the strongest factor in preventing, and possibly even reversing, tissue calcification involved in atherosclerosis, 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.

Studies have found associations between vitamin K2 intake and aortic calcification. Those diagnosed with severe aortic calcification had a lower intake of vitamin K2 compared with those with mild to moderate aortic calcification.

Kidney Health

Your kidneys have high concentrations of vitamin K2, which is used to activate MGP to remove calcium and prevent kidney stones from developing. Patients on hemodialysis are vitamin K-deficient. Recent studies showed that patients who consumed more vitamin K spent less time on dialysis and that patients who consumed more K while on dialysis had improved survival.

Brain Health

A vast majority of the vitamin K found in the human brain is vitamin K2. Vitamin K2 is also specifically concentrated to be higher in myelinated regions, while vitamin K1 is more randomly distributed. Vitamin K2 correlates with lipids in the brain called sulfatides, and the decline of both is associated with age-related neurological degeneration. Sulfatide levels in early Alzheimer’s patients are often over 90% lower than in healthy patients.  

Preventing Cancer

Dietary intake of vitamin K2 has been found to be inversely associated with overall cancer risk in men but not women. Specifically, both prostate (male only) and lung cancers were reduced in those who consumed the highest levels of vitamin K2. When these two cancer types were removed from the analysis, vitamin K2 intake still correlated with lower overall cancer risk.

Anticarcinogenic effects of vitamin K2 have been repeatedly demonstrated in cancer cell lines and are often attributed to menaquinones’ ability to regulate gene expression. Vitamin K2 in cell experiments induced cell death and/or inhibited the growth of breast, prostate, liver, colon, bladder, and ovarian cancers.  

Insulin Sensitivity

When bone is resorbed, vitamin K-dependent osteocalcin is released into the serum in an undercarboxylated form. Here, osteocalcin acts like a hormone on many tissues to improve insulin sensitivity and blood glucose.

In mice with metabolic syndrome, vitamin K2 treatment normalized blood glucose and also reduced anxiety and depression. Furthermore, higher intake of vitamin K2, but NOT of vitamin K1, was associated with a lower prevalence of metabolic syndrome, which usually includes insulin resistance and elevated blood glucose levels.

The benefits of vitamin K2 are myriad and extend well beyond these few health markers, including dental health, growth and development, and healthy skin.

Calcium Supplementation With K2 Deficiency

Vitamin K1 deficiency is rare and almost nonexistent, but vitamin K2 deficiency is more common.

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 fails to lower the risk of hip fracture in men or women—in fact, it may increase it.

Studies have found 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

It cannot  hurt to recommend eating 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. 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. You should not be afraid to include foods high in vitamin K2 despite their higher saturated fat content, especially if you 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. 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 you meet your 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, it is important to incorporate good sources of vitamin K2 into your diet to ensure proper calcium utilization in the body.