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College of Food, Agricultural, and Environmental Sciences


Chow Line: Some need to watch vitamin K intake (for 11/8/09)

October 30, 2009

A friend told me that she has started taking a certain type of medication and now she needs to avoid foods with vitamin K. Can that be right?

Well, sort of. Some people take a blood-thinner -- Warfarin or Coumadin, for example -- to reduce the risk of blood clots forming. They do need to pay attention to how much vitamin K they consume, because a sudden increase could reduce the effectiveness of the drug, and a sudden decrease could increase the blood-thinner's effects.

Guidance from the National Institutes of Health Drug-Nutrient Interaction Task Force suggests that people who are on this type of drug limit their intake of foods that have high or moderate amounts of vitamin K.

For example, limit raw parsley to a quarter-cup a day or cooked spinach, collards or other greens to a half-cup a day; you can have up to 1.5 cups of brussels sprouts or raw broccoli or 3 cups of raw spinach, romaine or green leaf lettuce a day. The key is to keep as consistent of a level of vitamin K in your diet from day to day as you can.

For a fact sheet with more information, go to the NIH's Clinical Center web site,, search for "vitamin K," and click on "Important Drug and Food Information." Or, for detailed information on vitamin K content in a wide variety of foods, go to the U.S. Department of Agriculture's National Nutrient Database at and click on "Nutrient Lists." Scroll down to vitamin K, and then click on "W" for a list of foods sorted by their vitamin K content.

Luckily, most people don't have to worry much about vitamin K. Deficiencies are rare and are usually seen only in people who are chronically malnourished or suffer from other conditions, such as celiac disease or cystic fibrosis, that cause problems with absorption of vitamins.

Still, the recommended intake for vitamin K is 90 micrograms a day for women and 120 micrograms for men, and the NIH estimates the average intake for most adults in the United States is just 70 to 80 micrograms a day. Getting more vitamin K might have benefits beyond the nutrient's standard blood-clotting role in the body. A review, published in a recent issue of Nutrition Research, of seven large studies indicates that higher amounts of vitamin K, up to 200 micrograms a day, might help improve bone quality and reduce the risk of fractures in post-menopausal women. However, more research is needed before these findings are firm enough to become part of standardized guidelines.

Chow Line is a service of Ohio State University Extension and the Ohio Agricultural Research and Development Center. Send questions to Chow Line, c/o Martha Filipic, 2021 Coffey Road, Columbus, OH, 43210-1044, or

Editor: This column was reviewed by Julie Shertzer, registered dietitian and program specialist for Ohio State University Extension in the Department of Human Nutrition, in the College of Education and Human Ecology.

Martha Filipic
Julie Shertzer