Diet & Nutrition
Dairy Products a Good Dietary Source of Some Types of Vitamin K
Research published in 2017 by scientists at the Jean Mayer USDA Human Nutrition Research Center on Aging (USDA HNRCA) at Tufts University in Boston shed new light on vitamin K and its significant presence in some dairy products available in the United States.
A release from the university reports that in the study, which appeared June 1st in Current Developments in Nutrition, researchers quantified the activity of two natural forms of vitamin K in dairy products of various fat contents and found that common U.S. dairy items including milks, yogurts and cheeses, contain appreciable amounts of multiple forms of vitamin K. Vitamin concentrations varied by fat content.
Vitamin K, which helps the blood to clot, is most commonly thought to come from leafy greens such as spinach, kale and broccoli. In fact, dietary sources of vitamin K are found in two natural forms: phylloquinone (PK, or vitamin K1), which is widely distributed through plant-based foods, and menaquinones (MK, or vitamin K2), which appear to be primarily in animal products and fermented foods. Almost all MK forms are also produced by bacteria in the human gut. Not much is known about MK amounts in U.S. dairy products.
The release quotes said Xueyan Fu, Ph.D., first and corresponding author and scientist in the Vitamin K Laboratory at the USDA HNRCA, as saying, “Dairy foods contain minute amounts of PK, the best known of the vitamin K forms, and so dairy is not commonly considered a rich dietary source for this nutrient. However, when it comes to MK forms, we found that dairy items already found in many peoples’ refrigerators are indeed a good dietary source for vitamin K.”
Guidelines for adequate vitamin K intake are based only on PK intake without consideration for other forms of vitamin K. MK differ from PK in structure in that they are compounds with different numbers of isoprenoid units in the side chain, designated as MK4 through MK13. Which forms of MK are present reflects which bacteria might be in the dairy products. Lactic acid bacteria, for example, are widely used in dairy and fermented foods.
To understand the presence of MK and PK in dairy products, the researchers used 50 nationally collected dairy samples provided by the USDA Nutrient Data Laboratory and 148 dairy samples purchased in 2016 from Boston area retail outlets. The products were divided into categories based on dairy types and fat content: milks, yogurts, Greek yogurts, kefirs, creams, processed cheeses, fresh cheeses, blue cheeses, soft cheeses, semi-soft cheeses, and hard cheeses. The effect of fat content on total vitamin K in all forms was compared using a two-sample T-test. The vitamin K content of cream products, for which the researchers had a smaller sample size, was analyzed using a general linear model, with heavy cream as the reference group.
Among the findings: