And although breast milk has a small amount of the nutrient, it's one of the few instances in which breast milk is simply not enough. So babies are generally given a shot of vitamin K at birth. The only other folks who need an extra boost of supplemental vitamin K are those who have a digestive disease such as cystic fibrosis, says James Sadowski, Ph.D., chief of the vitamin K laboratory at the Jean Mayer USDA Human Nutrition Research Center on Aging at Tufts University in Boston. But there are some folks who are afraid that they get too much vitamin K . Many people who are taking anticoagulants, or blood thinners, to prevent heart attack and stroke actually cut down on the amounts of green, leafy vegetables they eat because they're afraid that their lettuce will trigger the same events that their medications are trying to prevent.
Physicians tell a lot of people whom they put on anticoagulants to limit their vitamin K intakes.
I don't know why they do this, but it's fairly common. It is not good advice. Dr. Sadowski agrees. If someone is on oral anticoagulants because he has had a heart attack, a stroke or blood clots in his legs, he should keep his vitamin K consumption at a fairly constant level every day. But it probably doesn't matter how much he's getting as long as it's pretty close to the same thing every day.