Phylloquinone is a form of vitamin K found in green leafy vegetables and is the main source of vitamin K in the human diet. The bioavailability of vitamin K from vegetables has not been extensively researched and so relatively little is known about absorption and cellular uptake. Research1 published in the American Journal of Clinical Nutrition in 1999 investigated the bioavailability of phylloquinone in a cross-over design study involving 36 healthy men and women. The subjects consumed a mixed diet containing 100 µg of phylloquinone per day which was for 5 days supplemented with either broccoli (supplying 377 µg phylloquinone) or a phylloquinone supplemented oil (containing 417 µg phylloquinone). During this supplementation period phylloquinone plasma concentrations (as defined by percentage area under the curve) increased compared to the mixed diet. However, the response to the broccoli supplied phylloquinone was not statistically different from that in the supplemented oil.
These results suggest the whole foods are as bioavailable as supplements with reference to vitamin K absorption. This is not fully in agreement with previous research that has in some cases shown the absorption for oil-based supplement to be superior to vegetables. This might be expected based on the fact that vitamin K is a fat soluble vitamin. Worryingly, research suggests that the average diet in the United States does not supply sufficient vitamin K. Because green leafy vegetables are a good bioavailable source of phylloquinone, and because they contain other important phytochemicals, there consumption can be an effective way to improve the quality of the diet. The phylloquinone in this study was supplied by broccoli, and it may be that other foods possess less bioavailable phylloquinone due to preparation and biological plant differences. Therefore a range of green leafy vegetables should be consumed to allow for this.
RdB
