Study finds varying amounts of vitamin K in dairy products

By Mary Ellen Shoup

- Last updated on GMT

Varying amounts of vitamin K have been found in consumer dairy products, mostly in their full-fat varieties. ©iStock/DenizA
Varying amounts of vitamin K have been found in consumer dairy products, mostly in their full-fat varieties. ©iStock/DenizA

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Dairy products may be able to promote another key nutrient, vitamin K, as a study by Tufts University found that many full-fat dairy products contained an appreciable amount of the vitamin.

The study was conducted by researchers at the USDA Human Nutrition Research Center on Aging (HNRCA) and led by Dr Sarah Booth, senior scientist and director of the Vitamin K Laboratory at the USDA HNRCA and professor at the Friedman School of Nutrition Science and Policy at Tufts University.

The dairy industry promotes milk and milk products as good sources of nine essential nutrients: protein, calcium, vitamin D, vitamin A, vitamin B12, niacin, phosphorous, panthothenic acid, and riboflavin.

“This data suggests that vitamin K may be a 10th nutrient​,” Dr Xueyan Fu, study author and scientist II at the USDA HNRCA, told DairyReporter. 

“This is another 'feather-in-the-cap' for milk and milk products, providing additional support for those products as natural, nutrient-rich foods.”

Varying forms of vitamin K

Dietary sources of vitamin K are found in two natural forms: vitamin K1 (phylloquinone) and vitamin K2, known as menaquinones or MK – the latter being consumed in the diet or produced by bacteria in the gut.

Most knowledge of vitamin K is of phylloquinone, which is not present in dairy and therefore it was assumed that dairy products were not a contributor to vitamin K intake, Fu explained.

“With the availability of instruments that are very sensitive, our lab was able to develop a method to measure vitamin K1 and vitamin K2 together,”​ Fu said.

“This is the first report of vitamin K2 in dairy products in the US.”

Overlooked vitamin K

“Even though vitamin K is essential for life, there are still a lot of people who don’t know what vitamin K is or why we need vitamin K,”​ Fu said.

Consumer recognition of vitamin K is relatively low compared to other nutrients such as Vitamin D, but its presence performs important functions in the body such as chemically changing certain proteins and aiding blood clotting.

“There are very few researchers that study vitamin K,”​ Fu said. 

“As a result, we don’t have the critical mass to generate the research results that one sees for calcium and vitamin D.”

There is also evidence that low vitamin K intake is linked to an increased risk of osteoarthritis, according to Fu.

Procedure and findings

Researchers used 50 nationally collected dairy samples provided by the USDA Nutrient Data Laboratory and 148 dairy samples purchased in 2016 from Boston retail outlets.

The products were divided into categories based on dairy types and fat content: milk, yogurt, Greek yogurt, kefir, cream, processed cheese, fresh cheese, blue cheese, soft cheese, semi-soft cheese, and hard cheese.

Researchers found that all full-fat dairy products contained appreciable amounts of MK, primarily in the forms of MK9, MK10, and MK11.

In milk, the vitamin K concentrations varied by fat content; both total vitamin K and individual MK concentrations in full-fat milk were significantly higher than in 2% milk. PK was only detected in full-fat milk.

In cheese, the total vitamin K content varied by type, with soft cheese having the highest concentration, followed by blue cheese, semi-soft cheese, and hard cheese.

In yogurts, full-fat regular and Greek yogurt exhibited similar vitamin K concentrations as in full-fat milk; neither MK nor PK were detected in fat-free yogurt.

“Now we know menaquinones are abundant in dairy products, hence the US diet, this question of menaquinone metabolism becomes even more important to answer,”​ Fu added.


Source: Current Developments in Nutrition

Published online ahead of print:

“Multiple Vitamin K Forms Exist in Dairy Foods”

Authors: Xueyan Fu, Stephanie G. Harshman, Xiaohua Shen, David B. Haytowitz, J. Phillip Karl, Benjamin E. Wolfe and Sarah L Booth

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