Vitamin K1 is found primarily in green leafy vegetables. Vitamin K2 (menaquinone) is more difficult to obtain from the diet and is found mainly in egg yolks, organ meats, and natto, a fermented soy product commonly consumed in Japan that is exceptionally high in menaquinone. People living in regions of Japan where natto is frequently consumed tend to have very high levels of vitamin K2.
Vitamin K2 plays an important role in both bone and cardiovascular health because of its involvement in calcium regulation. Vitamin K–dependent proteins, such as matrix Gla-protein (MGP), help inhibit arterial calcification. Low vitamin K levels have been associated with an increased risk of atherosclerosis and heart disease.
A large population-based study published in the Journal of Nutrition (November 2004; 134:3100–3105) followed 4,807 subjects with no history of myocardial infarction at baseline (1990–1993) through January 1, 2000. Dietary intake of vitamin K2 was inversely related to the incidence of heart disease. Individuals consuming the highest amounts of vitamin K2 experienced a 57% reduction in death from heart disease compared to those with the lowest intake.
Vitamin K2 is also important for bone strength and may help prevent osteoporosis and fractures. A two-year study published in the Journal of Bone and Mineral Research (2000 Mar;15(3):515–521) examined the effects of vitamin K2 supplementation in 241 patients with osteoporosis. Participants were divided into two groups: one group received 45 mg per day of vitamin K2, and the other served as a control. The control group experienced a higher rate of fractures and lower bone density than the group receiving vitamin K2.
Vitamin K2 has even outperformed an osteoporosis medication in some studies. Research published in the Yonsei Medical Journal (2003 Oct 30;44(5):751–756) found that women taking 45 mg per day of vitamin K2 had a lower fracture rate than those treated with the drug etidronate.
