Did you know that vitamin K1 and vitamin K2 are different types of vitamin K? Before 2006, the USDA didn’t even distinguish K1 from K2 in foods, (1) but vitamin K2 plays important roles in our bodies—and you might not be getting enough. Read on to learn the difference between K1 and K2, the benefits of vitamin K2, and how to incorporate K2-rich foods into your diet.
On a nutrition label, vitamin K1 and vitamin K2 are both simply listed as vitamin K, even though our bodies don’t treat them identically. Vitamin K1 and K2 share the same chemical ring structure but have varying side chain lengths. (2) 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 thereby 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.
Vitamin K2 MK-4: Special Preference in Animals
Humans appear to have a unique preference for MK-4. All animals convert every type of vitamin K into vitamin K2 MK-4. The human placenta preferentially transports MK-4 over vitamin K1 across it, (3) and mammary tissue is the most efficient human tissue at converting vitamin Ks to MK-4, (4) further demonstrating its importance for humans.
Health Benefits of Vitamin K2
It should follow, then, that vitamin K intake decreases heart disease risk. The Rotterdam study found that in men followed for more than 15 years, the highest intake of vitamin K2 was associated with lower risks of severe aortic calcification, cardiovascular disease, and cardiovascular disease mortality. (7) Vitamin K1 content, however, had no association with heart disease risk, despite its intake being 10 times greater than that of K2.
The many hidden health benefits of vitamin K2.
The EPIC-NL cohort study with a follow-up of eight years showed that vitamin K2 intake in women was associated with lower risk of cardiovascular disease in a dose-dependent manner, meaning that every 10 micrograms/day consumed provided additional benefit. (8) Another study on postmenopausal women found that vitamin K2 intake was associated with decreased coronary calcification. (9) Again, vitamin K1 intake did not correlate with cardiovascular measures.
Vitamin K-dependent osteocalcin binds calcium to deposit in bone. MGP limits the sizes of calcium phosphate crystals to properly fit them into the bone matrix. (10) Because bone is constantly being formed and resorbed throughout our lives, adequate vitamin K intake is necessary for bone health.
Japanese postmenopausal women who consumed the most natto, the richest food source of vitamin K2, had less bone loss over time. (11) In a three-year RCT, 180 micrograms/day of vitamin K2 MK-7 helped mitigate postmenopausal bone loss over placebo. (12) Other RCTs either included pharmacologically high doses of vitamin K2 that would be impossible to obtain normally in a diet or were too short in duration. In one year, only 5 to 10 percent of bone is renewed in adults. (13) Therefore, shorter RCTs may not uncover the beneficial skeletal effects of vitamin K2.
Our kidneys have high concentrations of vitamin K2, which is used to activate MGP to remove calcium and prevent kidney stones from developing. (14) Patients on hemodialysis are vitamin K-deficient. (15) Recent studies showed that patients who consumed more vitamin K spent less time on dialysis (16) and that patients who consumed more K while on dialysis had improved survival. (17)
A vast majority of the vitamin K found in the human brain is vitamin K2. (14) Furthermore, vitamin K2 is specifically concentrated to be higher in myelinated regions, while vitamin K1 is more randomly distributed. (18) Vitamin K2 correlates with lipids in the brain called sulfatides, (19) and the decline of both is associated with age-related neurological degeneration. (20) Sulfatide levels in early Alzheimer’s patients are up to 93 percent lower than in healthy patients. (21, 22)
The EPIC-Heidelberg study followed more than 25,000 participants for eight to 10 years. (23, 24) Dietary intake of vitamin K2 was 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. (25) Vitamin K2 in cell experiments induced cell death and/or inhibited the growth of breast, prostate, liver, colon, bladder, and ovarian cancers. (26, 27, 28, 29, 30, 31, 32)
When bone is resorbed, vitamin K-dependent osteocalcin is released into the serum in an undercarboxylated form. (33) Here, osteocalcin acts like a hormone on many tissues to improve insulin sensitivity and blood glucose. (34, 35)
In mice with metabolic syndrome, vitamin K2 treatment normalized blood glucose and also reduced anxiety and depression. (36) 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. (37)
The benefits of vitamin K2 are myriad and extend well beyond this article, including dental health, growth and development, and healthy skin.
Can’t We Just Consume lots of Vitamin K1?
As mentioned earlier, animals do have the ability to convert vitamin K1 to vitamin K2 MK-4, but the conversion rates vary widely. (38, 39) In humans, the conversion rate is relatively unknown. Regardless, most people are deficient in vitamin K, hence infants in the United States are given a shot of vitamin K1 at birth to aid blood clotting. Furthermore, many drugs inhibit the conversion of vitamin K1 to K2, including cholesterol-lowering drugs (statins), osteoporosis drugs (alendronate, zoledronate), and blood thinners (warfarin). From the studies reviewed above, it’s clear that vitamin K2 intake itself is associated with many health benefits, regardless of vitamin K1 intake. Therefore, I wouldn’t rely solely on vitamin K1 intake to maintain healthy K2 status.
Foods High in Vitamin K2
Foods that are rich in vitamin K2 include:
- Natto, fermented soy
- Goose liver
- Egg yolks
- Dark chicken meat
I supply this list with a huge caveat—the source of the food means everything. Grass-fed cows yield higher K2 in milk and butter than grain-fed cows. Cheeses vary, as the vitamin K2 depends on what the cheese cultures produce. The same goes for fermented foods. For example, the bacteria used in making natto produce lots of MK-7 vitamin K2.
Vitamin K Synergies
Vitamin K2, as with other vitamins and minerals, is best consumed as part of a nutrient-dense, whole-foods diet. Because vitamin K is fat soluble, it must be eaten with fat for best absorption. (40)
Vitamins A and D are both activated by vitamin K2, allowing them to bind calcium to do their jobs. Weston A. Price in the 1940s was the first to discover the synergy of these three vitamins, although at the time he referred to vitamin K2 as “Activator X,” since its true identity was unknown until 2007. He used a combination of cod liver oil, rich in vitamins A and D, and butter oil, rich in vitamin K2, to treat a variety of modern diseases.
Magnesium intake is also important. Vitamins A and D induce gene expression, which is dependent on magnesium. Because processed foods contain very little, if any, magnesium, many people are deficient.
And for even more information on vitamin K2, check out Chris Masterjohn’s Ultimate Vitamin K2 Resource, with an extensive searchable database for vitamin K2 contents of food at the end.