Vitamin K was named by a Danish scientist Henrik Dam in the 1930s for its essential role in blood clotting (“Koagulation” in Danish). Vitamin K is so crucial for clotting that the World Health Organization recommends that all newborn babies (who naturally have very little vitamin K stored up) get a prophylactic dose to prevent rare but lethal outcomes from vitamin K deficiency bleeding.
But over the last few decades, we’ve learned that vitamin K does much more than regulate our blood. Gla proteins have been identified in different molecular structures throughout the body and serve a range of metabolic functions like building bones, preventing bone breakdown, preventing calcium blockages in blood vessels, eliminating unwanted or damaged cells, glucose metabolism, and even communicating between nerve cells. A 2019 review of clinical studies by Dr. Simes and colleagues published in International Journal of Molecular Sciences shows that vitamin K may even play a protective role in inflammation and oxidative stress independent of the Gla proteins. Vitamin K is a truly multi-functional vitamin.
TYPES AND SOURCES OF VITAMIN K
Vitamin K is present in a variety of foods, but the richest sources are from plants. All leafy green vegetables have vitamin K in the form of phylloquinone, or vitamin K1. Good sources of vitamin K1 include collards, spinach, cruciferous vegetables (e.g., broccoli and brussels sprouts), and herbs (e.g., cilantro and parsley).
AN EASY RULE OF THUMB IS THAT DARKER GREENS HAVE MORE VITAMIN K1.
It’s also available in smaller quantities from spices (e.g., paprika, chili powder, and cloves) and some plant oils like soybean and canola, as well as nuts. Vitamin K1 functions similarly to its namesake by participating in blood coagulation. A secondary form of vitamin K called menaquinones, or K2, is available in different structures named for their repeating molecular chains (e.g., MK-4, MK-7, MK-9). Unlike phylloquinones that only come from food, there are three ways that we get K2.
The primary way is through diet. Foods made with bacterial cultures like yogurt and cheese, or foods that are fermented like natto (from soy), sauerkraut (from cabbage), and pickles (from cucumbers) have the largest amounts of K2. Considerably smaller amounts are present in animal products like butter, meat, and eggs. Secondly, there are bacteria in the human gut that can synthesize small amounts of K2 (MK-5 to MK-15). Thirdly, our bodies can convert plant-based phylloquinones to MK-4 using a unique conversion process.
EVEN THOUGH OUR BODIES CAN CREATE VITAMIN K2 IN TWO DIFFERENT WAYS, WE DON’T MAKE ENOUGH, SO WE MUST EAT FOODS WITH VITAMIN K. VITAMIN K2 HELPS FORM GLA PROTEINS NEEDED FOR BONE, CARDIOVASCULAR, AND BRAIN HEALTH.
There is a third form, called menadione, or vitamin K3, which does not occur naturally in foods but has been synthesized as a supplement for livestock and pet feed, as some animals can convert this into K2 in their bodies. Vitamin K3 is not available for humans because of the risk of toxicity.
A LITTLE VITAMIN K GOES A LONG WAY
A very small amount of vitamin K is needed for optimal functioning. The European Food Safety Authority recommends an amount based on how much you weigh: 1 microgram (mcg) of vitamin K per kilo- gram of body weight per day. Health Canada’s Dietary Reference Intake and the US Dietary Recommended Intake for vitamin K was previously 1 mcg/kg but shifted to a simpler approach that does not require individuals to know their weight. The current daily vitamin K recommendation in Canada and the United States is 120 mcg for men and 90 mcg for women.
Dr. Guylaine Ferland, PhD, was a part of Health Canada’s advisory panel that developed the Dietary Reference Intake for vitamin K. Dr. Ferland is a professor of nutrition at the Université de Montreal and a scientist at the Research Centre of the Montreal Heart Institute. She runs a research program dedicated to vitamin K metabolism and the role of nutrition in the aging process.
According to Dr. Ferland, vitamin K recommendations are based on the minimum amount needed for coagulation, where 1 mcg/kg is certainly sufficient. While the recommended vitamin K intake for a 60 kg (132 lb) woman is 60 mcg in Europe and 90 mcg in North America, practically speaking, she points out that the difference is so small that it is equivalent to eating an extra floret of broccoli!
Our low but critical requirements for vitamin K, explained Dr. Ferland, can be linked back to the evolution of humans.
THE REASON WHY VITAMIN K IS REQUIRED IN SUCH SMALL AMOUNTS IS BECAUSE IT IS REQUIRED FOR COAGULATION. YOU DON’T FOOL AROUND WITH COAGULATION: IF YOU HAVE TOO MUCH, YOU GET A STROKE; IF YOU HAVE TOO LITTLE, YOU GET A HEMORRHAGE.
She remarked that humans would not have survived if we relied on large amounts of vitamin K from food, especially during times of famine in the course of history. Moreover, our bodies have evolved to recycle a large proportion of vitamin K, making the most of what we eat.
COMMON SOURCES OF VITAMIN K
The richest sources of vitamin K are vegetables, herbs, and fruit. Common sources and amounts from Health Canada’s Canadian Nutrient File* are listed below.
TO SUPPLEMENT OR NOT TO SUPPLEMENT?
With the availability of vitamin K through various foods plus our ability to store, produce, and recycle vitamin K, it is no surprise that most experts do not think taking vitamin K as a supplement is necessary.
“We have scientific evidence that vitamin K plays a role in various systems, but we are not at the stage of knowing whether a higher level of vitamin K than current recommendations would benefit brain health, vascular health, and so forth,” said Dr. Ferland. Currently, we do not have solid evidence for a dose-response relationship where vitamin K supplements are needed. Food is the most important way to get vitamin K and the nutrition needed to manage diseases.”
There are several dose-response clinical trials currently underway with different amounts and types of vitamin K supple- ments, different durations of study, and different biomarkers of vitamin K status, but for now there’s no way around it. You must eat your greens.
ANOTHER FACTOR TO CONSIDER IS THAT THERE IS A LIMIT TO HOW MUCH VITAMIN K YOUR BODY CAN STORE AND USE.
It is simply not true that if some is good, more will be better. “There is a very strong ceiling effect in nutrition, and this is especially the case with vitamins. We see this with vitamin K, D, and even calcium,” noted Dr. Ferland. After a certain point, consuming more vitamin K does not increase the amount in your tissues.
At the other end of the spectrum, it is rare but possible to be vitamin K deficient if you have very low intake of vegetables, if you suffer from a disease that affects nutrient absorption (e.g., bowel diseases like Crohn’s, liver disease, alcoholism), or if you have been using antibiotics for a prolonged period (because antibiotics destroy invader bacteria but also helpful bacteria in the gut).
Other factors that may affect your vitamin K status are medications. The anticoagulant called warfarin competes with the function of vitamin K in the body. When taking warfarin, patients are asked to keep their vitamin K intake constant so that it does not interfere with their blood-thinning medication. In any of these special circumstances, it is best to discuss your intake of vitamin K with your physician.
AIM FOR ADEQUATE INTAKE EVERY DAY
In a 2021 review of research on vitamin K published in Nutrition Reviews, Dr. Mladenka and colleagues explain that while current dose-response relationships for vitamin K are not clear enough to recommend higher intakes, too little intake of vitamin K and low levels of vitamin K in body tissues appear to be linked to health declines and disease. Accumulating research has explored the role of adequate vitamin K for the health of bones, brain, and the cardiovascular system.
BONE HEALTH
Vitamin K is required for the synthesis of several Gla proteins responsible for bone health, including osteocalcin. Adequate dietary vitamin K appears to be protective of bone quality and a risk of fractures. As an example, in a 2004 article by Dr. Booth and colleagues published in The Journal of Clinical Endocrinology and Metabolism, low plasma levels of phylloquinone, or vitamin K1, were linked to low bone mineral density at the hip for men, and at the spine for postmenopausal women not using estrogen replacement. No associations were seen for premenopausal or postmenopausal women with estrogen, suggesting an interplay between estrogen status and vitamin K status.
A meta-analysis of nearly 81,000 participants by Dr. Hao and colleagues published in the journal Medicine showed that those with the highest intake of dietary vitamin K had the lowest risk of fractures. This meta-analysis included peer-reviewed research from the United States, Denmark, Norway, and China between 1999 and 2012, and looked exclusively at phylloquinone intake among adults over age 30.
BRAIN HEALTH
Regarding brain health, scientists have identified vitamin-K-dependent proteins that have neuroprotective effects, regulate communication between nerve cells, and even regulate cell growth.
ACCUMULATING EVIDENCE SUGGESTS THAT ADEQUATE DIETARY VITAMIN K IS PROTECTIVE OF COGNITIVE FUNCTION AND HAS A ROLE IN PREVENTING DEMENTIA.
For instance, in a sample of 320 older adults free of cognitive impairment, Dr. Presse and colleagues showed that those with a high phylloquinone status showed better verbal episodic memory performance (e.g., memory of events) compared to those with low phylloquinone status. This 2013 study used data from the Québec Longitudinal Study on Nutrition and Successful Aging and was published in Neurobiology of Aging.
More recently, a 2022 study by Dr. Booth and colleagues in the journal Alzheimer’s & Dementia found that higher vitamin K2 concentrations (MK4) in the brain of 325 participants was associ- ated with a 17-20% lower risk of dementia or mild cognitive impair- ment. Data were based on the Rush Memory and Aging Project (MAP), a longitudinal study in the Chicago area that examines genetic and environmental risk factors for Alzheimer’s disease.
Higher concentrations in specific regions were linked to better cognitive function scores before death and slower rates of cognitive decline. Circulating phylloquinone was also associated with better cognitive function and slower rates of cognitive decline. Authors suggested that if well-designed follow-up studies could determine mechanisms for dietary vitamin K slowing cognitive decline, this could have a significant public health impact.
CARDIOVASCULAR HEALTH
There are vitamin-K-dependent proteins like matrix Gla protein that help inhibit blood vessel calcification. In this way, scientists have hypothesized that vitamin K has a role in preventing cardio- vascular diseases. A 2017 review of observational and clinical studies by Drs. van Ballegooijen and Beulens published in Current Nutrition Reports summarizes key evidence showing that low vitamin K status may increase risk factors for cardiovascular disease.
Though findings were mixed for healthy populations, low vitamin K status appeared to have the most detrimental effects for groups with comorbidities, like Type 2 diabetes, hypertension, and kidney disease, which are risk factors for cardiovascular disease.
A 2021 review in Advances in Nutrition by Dr. Shea and colleagues supports that rigorous and reproducible studies are still needed before we can conclude that vitamin K is cardio-protective and the amount needed for cardio-protection. At the same time, because vitamin K is found primarily in leafy green vegetables and plant oils, adequate vitamin K intake usually reflects healthy diets and lifestyles, which are inherently cardio-protective. It may not be possible to eliminate these confounding effects fully.
Overall, our bodies need vitamin K to function optimally throughout our lifespan. Much of the research on the benefits of vitamin K points to the importance of adequate intake. While vitamin K deficiency has been seen to impair a range of metabolic systems, data are inconclusive about whether additional vitamin K intake beyond recommended amounts through diet will have clear benefits. What we do know is that foods rich in vitamin K are part of a healthy, balanced diet, so be sure to get enough every day.
To read the original article visit page 11 of Mind Over Matter Magazine Vol. 17
