Lettuce is an important source of many important vitamins and nutrients, including vitamin K. Vitamin K's role in blood clotting and bone health make it an essential component to good health. And since the primary source of vitamin K is food, preparing meals with lettuce and other green, leafy vegetables is a good health practice.
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Vitamin K Basics
Vitamin K is needed to make and activate proteins involved in the process of blood clotting and bone density. When you lack vitamin K, blood loss from injury increases and, accordingly, your chance for death rises. Too little vitamin K also puts you at greater risk for bone fractures. Good sources of vitamin K include spinach, turnip greens, collards, kale and lettuce.
Lettuce and Vitamin K
Though lettuce may not provide as much vitamin K as other sources, such as spinach and turnip greens, it's still a good source. Different types of lettuce provide different amounts of vitamin K. One cup of iceberg lettuce provides 14 micrograms of vitamin K, a cup of green leaf lettuce offers 63 micrograms, while one cup of romaine lettuce contains 57 micrograms, giving support to darker heads of lettuce providing more nutrients. However, these lettuces' vitamin K content pales in comparison to that of other greens -- a cup of raw kale, for instance, contains 547 micrograms of vitamin K, while 1-cup servings or raw spinach or chard offer 145 or 299 micrograms, respectively.
Vitamin K and Blood Thinners
Lettuce and other foods rich in vitamin K need to be carefully consumed when on blood thinning medications. The mechanisms of these drugs are sensitive to vitamin K levels in the body. If you're on a blood thinner, you can't consume either too much or too little vitamin K on a daily basis. It's best to keep vitamin K intake stable from day to day if you're on such medications.
The Institutes of Medicine recommends adult men consume 120 mcg of daily vitamin K and women consume 90 mcg. Not eating enough lettuce salad or other green, leafy vegetables puts you at risk for vitamin K deficiency, notes the Harvard School of Public Health. Make lettuce and other green, leafy vegetables a part of your daily menu. Using a bit more than two cups of romaine lettuce in a salad will exceed your daily requirement of vitamin K if you're an adult male.