By Kyla Shea, Tufts University
When Danish scientist Henrik Dam was giving chicks a cholesterol-free diet in his laboratory about 90 years ago, he noticed excessive bleeding in some of them. It didn’t stop after he replaced the cholesterol. Dam eventually concluded that the bleeding was related to “depletion of an anti-hemorrhagic compound,” which he called vitamin K (for “coagulation,” as it is written in Danish). For this discovery, Dam received the 1943 Nobel Prize in Physiology or Medicine.
Most people are familiar with vitamins A, B, C, D, and / or E, but vitamin K is slipping under the nutritional radar. However, it is vital as the blood must clot normally. Scientists are now realizing that there is more to know about this less valued nutrient.
Today, the Jean Mayer USDA Human Nutrition Research Center on Aging at Tufts University is home to the only research team in the world dedicated exclusively to vitamin K nutrition. I am a scientist on this team. We study how foods provide vitamin K to support healthy aging.
Why is vitamin K important?
In the past few decades, scientists have discovered vitamin K-dependent proteins in many tissues in the body. This suggests that vitamin K plays a physiological role that goes well beyond blood clotting. For example, proteins that are dependent on vitamin K in arterial tissue can help prevent calcification. This is critical as arterial calcification can lead to heart attacks.
Without vitamin K, these proteins cannot prevent calcification. And because these proteins are present in cartilage and bones, we are also investigating how these vitamin K-dependent proteins can be involved in osteoarthritis.
Just as there are different forms of B vitamins, there are also several forms of vitamin K. Scientists know at least 12. Phylloquinone, also known as vitamin K1, is synthesized by plants. Leafy green vegetables such as spinach and cabbage vegetables as well as vegetable oils such as soy and rapeseed oil contain high amounts of phylloquinone.
Menaquinones, a class of vitamin K compounds also known as vitamin K2, are found in variable amounts in animal foods, such as dairy products and some meats. Menaquinones are also produced by gut microbiota, although their nutritional value is uncertain.
Our laboratory measured the amount of vitamin K in thousands of foods commonly consumed in North America. In partnership with the US Department of Agriculture, this information is publicly available on the USDA’s Food Data Central website, the world’s most comprehensive nutrition database. Over 350,000 foods are profiled.
One goal of our research is to establish a recommended food intake for vitamin K. In North America, current dietary recommendations for vitamin K are referred to as “adequate intake,” the amount that is consumed to ensure adequate nutrition. Adequate intake is established when insufficient There is scientific evidence for a more accurate recommended food intake. For men over the age of 18, the adequate intake of vitamin K is 120 micrograms per day. For women, 90 micrograms per day. One cup of raw spinach contains 145 micrograms of phylloquinone. Patients taking warfarin should contact their doctor for information about vitamin K intake.
Coagulation disorders due to low dietary vitamin K intake are extremely rare, as almost everyone consumes enough vitamin K in their diet to maintain normal clotting. Although recent evidence suggests that low vitamin K intake may affect health outcomes unrelated to clotting, these findings do not currently support the need to take vitamin K supplements even though they are in the marketplace. Menaquinone supplements have become particularly popular because they are claimed to have unique health benefits that phylloquinone does not.
However, it is very difficult to isolate the effect of a nutrient on health outcomes, and even more difficult to recommend the use of dietary supplements based on the studies conducted so far. Large clinical trials need to be designed to answer the question. These studies, which can cost millions, haven’t been done with vitamin K. The smaller studies that have been conducted do not meet the standards of scientific accuracy needed to promote vitamin K supplements at this point in time.
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As our research progresses, we seek to better understand the role of vitamin K in human health beyond clotting. We want to know how much vitamin K is needed to protect against age-related diseases and disabilities. However, until we have stronger evidence that supplements are needed, getting vitamin K from food is safer and more convenient.
All opinions, results, conclusions, or recommendations expressed in this publication are those of the author and do not necessarily reflect the views of the USDA.
Kyla Shea, Scientist I, Vitamin K Research Team at the USDA Human Nutrition Research Center on Aging at Tufts University, Tufts University
This article is republished by The Conversation under a Creative Commons license. Read the original article.