The supplement used in the study, supplied by CLA developer Norway's Natural, is a proprietary extract of natto that provides the vitamin K2 as menaquinone MK-7. Natural markets the ingredient under its Natto K2 brand.
Dr Cees Vermeer, lead researcher, said: "This study is the first of its kind comparing a vitamin K2 extract in supplement form to ordinary vitamin K supplements for bone health. These findings build on the existing body of evidence supporting vitamin K2 as an important form of vitamin K with benefits that extend beyond K1 alone."
The study, carried out at the University of Maastricht, Netherlands involved participants receiving supplements of vitamin K1 or K2 (as menaquinone-7 from Natto K2)in equivalent doses over a six-week period.
Researchers found that much higher circulating vitamin K levels werereached with Natto K2 than with K1. Circulating under-carboxylatedosteocalcin (a marker for hip fracture risk) was decreased much more by K2 than by K1.
The ratio between carboxylated and under-carboxylated osteocalcin - this ratio being a marker for bone vitamin K status - improved similarly with both forms of vitamin K, although in the case of K1 a clear plateau was reached, whereas in the case of K2 the curve was still rising after six weeks of administration.
Since high bone turnover is a strong risk factor for acceleratedbone loss, Vermeer suggests that K2 may have a second protective effect, contributing to decreasing bone turnover.
Natto, a traditional Japanese food, is fermented from soybeans and extracted via a proprietary process and then manufactured into a pure natto extract ingredient.
In the Caucasian population the extract has shown a significant benefit in the reduction of heart disease, due to its roles in calcium use and promoting matrix Gla-protein activity, a potent inhibitor of vascular calcification, claims Natural.
K2 is available to US dietary supplement manufacturing and marketing partners as an encapsulated product with Natural retaining sole rights to market this extract in North America, under its own trademark name Natto K2.