A. Sarah L. Booth, PhD, senior scientist and director of the Vitamin K Laboratory at Tufts’ HNRCA, responds: “Vitamin K is a family of nutrients with a similar chemical structure. These compounds include phylloquinone (vitamin K1) and chemicals called menaquinones (vitamin K2). You get K1 mostly from green leafy vegetables, such as spinach and kale. Vitamin K2 is found in modest amounts in animal-based and fermented foods, such as cheese and fermented vegetables.
“Vitamin K plays a role in the body’s synthesis of proteins involved in blood clotting and bone metabolism. It’s link to clotting function is why people who take the blood thinner warfarin (Coumadin) need to avoid swings in their intake of vitamin-K-rich foods, which can affect the action of the drug.
“There are some observational studies that suggest a link between some forms of vitamin K2 and reduced risk for bone loss and heart disease. However, the data have relied on indirect ways to measure the level of vitamin K2, which makes it hard to be sure exactly how much vitamin K2 study participants actually have in their blood. In addition, there are very few clinical trials to establish a cause-and-effect relationship between vitamin K2 levels and bone or heart health; such studies have also relied on a single form of vitamin K2 that is not common in the diet.
“Until more rigorous studies are conducted, you can just make sure to get adequate amounts of vitamin K from your diet.”