Special k: find out why vitamin K is key for treating osteoporosis, controlling blood sugar, and maybe even preventing cancer.(SUPPLEMENTS: SHOP SMART)(Report)

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THE BASICS: Vitamin K has been known since the 1930s as the "coagulation" vitamin because it is essential for normal blood clotting. But recent research has shown that vitamin K supplements can have striking benefits in preventing and reversing osteoporosis, controlling blood sugar, and maybe even reducing the risk of cancer and coronary heart disease.

ALIAS: Vitamin K terminology can get very confusing. The two principal types of vitamin K supplements are K1 and K2. Vitamin K1 (phylloquinone) is found in leafy green vegetables. Vitamin K2 occurs in two forms, MK-4 (menatetrenone-4) and MK-7 (menaquinone-7). The MK-4 form of vitamin K is found in egg yolks, egg mayonnaise, chicken thighs, and dairy products. The MK-7 form of vitamin K is found in natto, a type of fermented soybean food (also sold as a supplement).

HOW VITAMIN K WORKS: Most of vitamin K's benefits derive from its role in making several key proteins, particularly osteocalcin, needed for strong bones. More technically, vitamin K promotes the carboxylation of osteocalcin. (Carboxylation adds one carbon, one hydrogen, and two oxygen atoms.) Without carboxylation, these proteins cannot do their jobs. Vitamin K is also required for matrix Gla protein (MGP), and animal studies suggest that MCP helps regulate where the body deposits calcium.

HEALTH BENEFITS: Over the past several years, research has revealed multifaceted benefits to vitamin K. Here are the highlights:

Bone health. Low intake of vitamin K interferes with normal bone development and increases the risk of broken bones and osteoporosis. Both Dutch and Japanese researchers have used large amounts of vitamin K2 daily to treat and successfully reverse osteoporosis in women. Nearly all of these studies used 45 mg daily of the MK-4 form of vitamin K2. Vitamin K also reduces bone loss caused by cortisone, blood-thinning drugs, menopause, diabetes, and other health issues.

Blood sugar. In 2007, Columbia University researchers discovered that the bone protein osteocalcin also functions as a hormone. Osteocalcin regulates the number of insulin-producing cells in the pancreas, the secretion of insulin, sensitivity to insulin, and the size of fat cells. Of course, vitamin K is needed to make osteocalcin.