The U.S. Recommended Dietary Allowance is 1 mcg per kilogram body weight. However, a recent study suggests that a higher intake of vitamin K, in the range of 110 mcg daily, might be helpful for preventing osteoporosis. Kale, green tea, and turnip greens are the best food sources, providing about 10 times the daily adult requirement in a single serving. Spinach, broccoli, lettuce, and cabbage are very rich sources as well, and you can get perfectly respectable amounts of vitamin K in such common foods as oats, green peas, whole wheat, and green beans, as well as watercress and asparagus. Pregnant women, newborn babies, and postmenopausal women are also sometimes deficient in this vitamin.
Alcoholism can also lead to vitamin K deficiency.
For some purposes, vitamin K has been recommended at a daily dose of 150 to 500 mcg. Although such dosages are much higher than required for nutritional purposes, they are not out of the range of what can be reached through eating plenty of green leafy vegetables. Recent evidence suggests that vitamin K supplements can be helpful for preventing osteoporosis. Based on its ability to help blood clot normally, vitamin K has been proposed as a treatment for excessive menstrual bleeding. However, the last actual study testing this idea was carried out more than 55 years ago.