In combination with calcium and magnesium, they help increase bone strength as well. (blog.wellnessfx.com)
They are important for bone strength because of their ability to drive calcium into the tissues (i.e.: bone) from the blood. (robdaquila.com)
Vitamin K2 has also been shown to be an important factor in improving bone strength by binding calcium and other minerals to bone. (naturalhealth365.com)