Natural Factors Vitamin K2 features vitamin K2 as menaquinone-7 (MK-7), an advanced, fat-soluble form of vitamin K that serves multiple functions in the body. The K family consists of a trio of vitamins: K1 (phylloquinone), naturally occurring in leafy green vegetables and plant oils; K2 (mena-quinone) present in butter, cows liver, eggs, certain cheeses and natto, a fermented soybean food; and K3, a synthetic form of the vitamin. K3 has been shown to have toxic effects on the liver and K1 doesn’t have adequate benefits for calcium metabolism to dramatically improve osteoporosis or atherosclerosis. Only K2 in the form of MK-7 has been shown to offer 24-hour protection from a single daily dose. Other commercially available subtypes of K2, such as MK-4, only last four to six hours in the body and are required in much larger dosages to be effective.