Lurking among our dietary leafy greens is a key fat-soluble vitamin that allows humans to form bones and clot blood—vitamin K. Vitamin K's role in bone health has been the subject of many headlines lately, especially after research shows few get enough of it. Although one cup of spinach contains two times the current RDA (about 120mcg), recent research shows vitamin K may not be as abundant as once thought and, therefore, many may be experiencing deficiencies. A survey by the USDA Human Nutrition Research Center on Aging at Tufts University found that people between the ages of 18 and 44 do not ingest enough vitamin K.
Vitamin K helps to regulate calcium, keeping it in the bones and out of the arteries; this action also helps stop osteoporosis and heart attacks. The vitamin does this by mediating a type of protein that controls calcium, gamma-carboxyglutamic acid. Vitamin K also is a mediator of gamma-carboxylation, which means it enhances the activity of glutamyl residues on certain bone proteins, such as osteocalcin. Essentially, vitamin K helps these proteins hold on to calcium.