Presently there are three forms of K vitamins available in dietary supplements: synthetic vitamin K1, synthetic vitamin K2 as menaquinone-4 (MK-4), and natural vitamin K2 as menaquinone-7 (MK-7). The last is the most bioavailable, bioactive, and longest lasting form of vitamin K.
It has uniquely effective and quite astounding benefits on bone metabolism and bone growth.
Vitamin K2 is preferred by the extra-hepatic tissues (bone, cartilage, vasculature) and this may be produced as MK-4 by the animal from K1, or may be of bacterial origin (MK-7, MK-9, and other MK numbers). The latter may be consumed already prepared by bacteria (see below). Discussion is ongoing as to what extent K2 produced by intestinal bacteria contributes to daily vitamin K2 needs. If, however, intestinal bacterial supply was enough to supplement all tissues needing K2, we would not find high fractions of undercarboxylated Gla-proteins in human studies.
Natural K2 is also found in bacterial fermented foods, like mature cheeses and curd. The MK-4 form of K2 is often found in relatively small quantities in meat and eggs. The richest source of natural K2 is the traditional Japanese dish natto made of fermented soybeans and Bacillus subtilis, which provides an unusually rich source of K2 as long-chain MK-7: its consumption in Northern Japan has been linked to significant improvement in K vitamin’s status and bone health in many studies. The intense smell and strong taste, however, make this soyfood a less attractive source of K2 for Westerners’ tastes. Supplement food companies sell nattō extract, standardized for K2 content, in capsules. It is not known whether B. subtilis will produce K2 with other legumes (chickpeas, beans, lentils).
Food sources of vitamin K2 include fermented or aged cheeses, eggs, meats such as chicken and beef and their fat, livers, and organs, and in fermented vegetables, especially natto, as well as sauerkraut and kefir
All data available at this time demonstrate that vitamin K has no adverse effects in healthy subjects.
None are recorded.
Source: Wikipedia, https://en.wikipedia.org/wiki/Vitamin_K2