What it is
This fat-soluble vitamin is essential for normal blood clotting and has two forms. Vitamin K1 (phylloquinone or phytonadione) is found in green leafy vegetables, such as lettuce, broccoli, and spinach, and accounts for most of the vitamin K in a typical Western diet. The rest is made up of vitamin K2 (menaquinone), found in meat, cheese, and fermented soybeans.
Helps prevent and treat osteoporosis by boosting bone density. K1 may also improve heart health in postmenopausal women and reduce prostate cancer risk in men.
Research performed at the USDA Human Nutrition Research Center in 2008 found that supplementing with 500 mcg of vitamin K1 for three years reduced the development of insulin resistance in men ages 60 to 80, suggesting that high doses of the vitamin may help protect against diabetes.
How to take it*
The dietary reference intake for K1 and K2 combined is 120 mcg per day for men and 90 mcg per day for women. A balanced diet offers sufficient amounts. Talk to your doctor if you are pregnant, breast-feeding, or taking blood thinners. High doses can upset digestion and cause allergic reactions.
*Talk with your health care provider before starting any supplement regimen.