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The right dose of Vitamin K
Unfortunately, there's no perfect study to guide just how much Vitamin K is too much for those taking Coumadin. Most physicians recommend limiting foods that contain very high or even moderate amounts of Vitamin K. At the same time, there's never been a recommendation to severely limit Vitamin K intake.

Why do Vitamin K levels vary in the same foods?
The difference occurs not because there is a change in the amount of Vitamin K but that the volume of cooked broccoli is less than when it is raw. The results that the USDA gives for cooked foods are measured after the food is cooked.

How Many Micrograms of Vitamin K Should I Have Per Day?
The Recommended Daily Allowance (RDA) for Vitamin K is 85 micrograms (mcg) per day. Most physicians recommend trying to keep levels no higher than this as a consequence of the effect that higher doses can have on INR levels.


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How well is Vitamin K absorbed?

Recent studies suggest that the average American diet does not contain enough Vitamin K, which contributes to proper blood coagulation. Since phylloquinone, the primary source of Vitamin K in plants and plant oils, is soluble in fat, researchers have long assumed that phylloquinone would be more easily absorbed from an oil than from a vegetable source. Further, indicators of Vitamin K status in the blood or urine are different in younger adults than in older adults.

Researchers at Tufts University developed a crossover study to test whether phylloquinone is more easily absorbed from an oil than a vegetable and whether that absorption would vary by age (Am J Clin Nutr 1999;70(3):368-77). A group of 36 healthy volunteers, male and female, were separated by sex and then further into two groups by age: 20-40 years of age and over 60 years of age.

Each group took up residency at the University's Jean Mayer USDA Human Nutrition Research Center on Aging for three sets of 15 days and ate all their meals there: a diet designed to maintain their weight and fulfill their nutritional needs from common foods in the American diet ("mixed diet"). Each residency period was separated by 6 weeks of living at home and eating their regular diet.

For one residency period, each group ate only the mixed diet. For another residency period, on days 6-10 of the residency period each group was given an extra ~3.5 ounces of microwaved broccoli at the lunch and dinner meals. For yet a third residency period, also during days 6-10, their lunch and dinner meals were made with a Vitamin-K-fortified corn oil. The subjects' blood and urine were tested regularly to monitor their Vitamin K levels throughout the study.

To their surprise, the researchers found that there was no significant difference in absorption between supplementation with the fortified corn oil or the broccoli. Nor was there a significant difference between the age groups.

What this means for you:

Getting enough Vitamin K in your diet is as easy as eating broccoli, cabbage or romaine lettuce each day.

For those on Coumadin® (warfarin), eating a healthy diet is key to getting enough, but it's important that you be careful with foods that are very high in Vitamin K. Here's a list of all the foods that are used in Dr. Gourmet recipes and their amounts of Vitamin K in micrograms (PDF document). Either way, your age doesn’t seem to matter as Vitamin K is absorbed at the same rate no matter if you are 17 or 71.

First posted: August 22, 2006