The new study, published on-line ahead of print in the journal Blood and partly funded by Natural ASA, reported that vitamin K2 in the form of menaquinone-7 (MK-7) from natto was more effective in both promoting markers of bone health, and counteracting vitamin K antagonists.
"For the food industry, an alternative to increasing the recommended dose would be introducing on a larger scale the more potent MK-7 instead of K1 in functional foods and multivitamin supplements," wrote lead author Leon Schurgers.
There are two main forms of vitamin K: phylloquinone, also known as phytonadione, (vitamin K1) which is found in green leafy vegetables such as lettuce, broccoli and spinach, and makes up about 90 per cent of the vitamin K in a typical Western diet; and menaquinones (vitamins K2), which make up about 10 per cent of Western vitamin K consumption and can be synthesised in the gut by microflora.
Menaquinones (MK-n: with the n determined by the number of prenyl side chains) can also be found in the diet; MK-4 can be found in animal meat, MK-7, MK-8, and MK-9 are found in fermented food products like cheese, and natto is a rich source of MK-7.
Some sources have said that MK-4, also known as menatetrenone, is synthetic vitamin K2, which is not correct. However, MK-4 is distinct from other MKs because it not a major constituent of the spectrum of MKs produced by gut microflora, but can be derived from K1 in vivo.
A synthetic form of vitamin K, known as K3, does exist but is not recommended for human consumption.
"This is the first human study using natural vitamin K2 as a dietary supplement. Clearly Natural Vitamin K2 as menaquinone-7 is the most beneficial vitamin K that one could take. Large scale human studies have shown that eating foods rich in Vitamin K2 significantly promotes bone health, reduces risk of bone injury, and significantly promotes cardiovascular health," said Schurgers in a release.
The findings from the new research, by researchers from the University of Maastricht and the University Hospital Maastricht, were based on four separate studies. The first of which looked at the bioavailability after oral intake of both vitamin K1 (Konakion, Roche) and K2 (N-ZymeCeuticals) by 15 volunteers.
The Maastricht-based researchers report that both blood levels peaked after four hours. However, the levels of vitamin K1 were 86 per cent lower after only eight hours, while K2 (MK-7) levels were only 50 per cent lower after 68 hours, showing slower excretion from the body.
The second study involved ten volunteers given increasing doses of either K1 or K2. Four hours after consuming the supplement, blood levels of the vitamins showed a dose-respondent effect, but only the K2 still had an effect 24 hours later.
"This means that - if taken in single daily doses of 100 micrograms - only MK-7 is effectively present in the circulation and available for absorption by various tissues during the 24 hours following intake," wrote the researchers.
The third study looked at blood levels of both vitamins amongst 18 volunteers after six-weeks of supplementation (0.22 micromoles per day). Schurgers and his co-workers report that despite equal doses only the MK-7 produced a stable plateau above six micromoles per litre of blood, while the K1 supplement produced stable blood levels slightly above placebo levels.
Bone turnover was also measured in this study (measured as a ratio of circulating carboxylated and uncarboxylated osteocalcin), and the researchers report that both forms of vitamin K showed activity after three days. However, vitamin K1's effect did not increase further while MK-7's effect increased over the six-week period.
"Menaquinone-7 has a very high bioavailability, a very long plasma half life time, and as a consequence also a very high bioactivity in activating vitamin K-dependent proteins like osteocalcin and matrix gla-protein," Schurgers told NutraIngredients.com.
The fourth and final study looked at the effect of the supplements on different doses of the blood-thinning drug and vitamin K-antiagonist acenocoumarol. By measuring the response to vitamin K supplementation the researchers attempted to measure the activity of vitamin K in the body.
The researchers report that MK-7 was much more potent, demonstrating a superior bioactivity.
"Haematologists, on the other hand, need to be aware that relatively low doses of MK-7 may have a larger impact on the stability of oral anticoagulation than vitamin K1," wrote Schurgers.
Source: Blood First Edition Paper Published on-line ahead of print. doi: 10.1182/blood-2006-08-040709 "Vitamin K-containing dietary supplements: comparison of synthetic vitamin K1 and natto-derived menaquinone-7" Authors: L.J. Schurgers, K.J.F. Teunissen, K. Hamulyak, M.H.J. Knapen, H. Vik, and C. Vermeer