When the subject of vitamin K comes up among healthcare professionals, it is more often than not in a conversation about coagulation. In fact, even the name vitamin K derives from the German word for coagulation, koagulation, according to researchers at the University of Maryland Medical Centre. In the US, UK and Canada, all babies receive vitamin-K injections to prevent the possibility of bleeding from the brain, as they are born without the K-generating intestinal bacteria from which the rest of us benefit.

Over the years, however, growing numbers in the nutrition industry have been trumpeting vitamin K as a therapy for a growing range of conditions, from osteoporosis to atherosclerosis, and even some types of cancer. The variety of vitamin K with the most potential, as far as most of these claims is concerned, is MK-7 subtype vitamin K2, also known
as menaquinone.

Vitamin K2 was discovered in 1945 by Dr Weston Price, the first to describe a “new vitamin-like activator”, which he named Activator X. Fat soluble and present in certain animal products, such as fish eggs and butterfat from cows fed green grass, Price came to the conclusion that this substance could help activate minerals in the body that could protect from tooth decay, prevent heart disease and improve the brain’s function, among other qualities. He also believed that the absence of this substance from diets of the time was a cause of many of the biggest health problems.

Price died before he was able to properly identify this mysterious substance. But years later, it emerged that a group of Russian scientists were using the same detection test that Price had used to find Activator X to successfully detect benzoquinone, which is in the same compound class as vitamins K1 and K2. Today, there is something of a consensus that what Price discovered was in fact vitamin K2.

K1 and K2: important differences

K1 and K2 are structurally similar but rather different in terms of where they can be found and the role that they play. K1 is found only in plants while vitamin K2 is produced by intestinal bacteria and found in some animal products and fermented foods. Natto, a Japanese dish made of fermented soybeans, represents an unusually rich source of vitamin K2, containing 1,103μg per 100g. The next richest in K2 is goose liver pate, with 369μg per 100g, according to Vitamin K2 and the Calcium Paradox, a 2012 book by Kate Rhéaume-Bleue.

While vitamin K1 is primarily useful for coagulation, a number of studies have shown that K2 acts as a kind of enabler of other minerals in the body: for example, working with vitamin D to push calcium ions from the blood into the bones. K2 helps direct the vitamin D to the right place and stops it from building up on the walls of the arteries. Nutritional guidelines in the UK don’t yet recommend the taking of vitamin K2 to help avoid calcification, but a growing evidence base suggests this could one day change.

"A number of studies have shown that K2 acts as a kind of enabler of other minerals in the body." 

“Vitamin D is a hot-button topic at the moment,” says Rick Miller, nutrition manager at the a2 Milk Company, independent clinical and sports dietician, and representative of the British Dietetics Association. “But if you take too much, it can lead to calcium build-up in the arteries and that’s atherosclerosis, a process that leads to cardiovascular disease. Vitamin K plays a role in making sure those calcium ions get to where they want to go.”

A few studies also point to the use of K2 to help improve bone strength and reduce the risk of fracture. Scientists from the Research Institute and Practice for Involutional Diseases in Nagano, Japan, enrolled 241 osteoporotic patients on a 24-month randomised open-label study. 120 of these subjects were orally administered 45mg a day of vitamin K2, the rest didn’t receive any; both groups were monitored for lumbar bone mineral density (LBMD) and the occurrence of new clinical fractures. The study concluded that the group treated with K2 was less prone to new fractures, “although the vitamin failed to increase LBMD”.

Another study was carried out in 2013 by scientists at Maastricht University: 244 postmenopausal women received either a placebo or 180μg a day of MK-7 (a strand of K2) for three years. The bone-mineral density of lumbar spine, total hip and femoral neck was measured at the start and after one, two and three years of treatment. The study found that MK-7 intake helped arrest the age-related decline of bone mineral density, and bone mineral content of the lumbar spine and femoral neck, but not of the total hip. “MK-7 supplements may help postmenopausal women to prevent bone loss,” the study concluded.

“There have been a number of studies on bone density; most of them double blind, and with men and women typically middle aged or older,” Miller says. “The mean effect is that there is an increase in bone mineral density beyond what you would expect with calcium density. It’s [taking vitamin K2] a worthwhile thing to consider if there is a risk of losing bone density, maybe in postmenopausal women, the elderly, or individuals with a not particularly good dietary intake who are at risk of losing bone tissue.”

A few studies have also raised optimism about the use of K2 to treat certain types of cancer. In 2006, researchers at the Department of Internal Medicine at the Saga Medical School in Japan tested the effects of menatetrenone on the reoccurrence rate of hepatocellular carcinoma (HCC), the most common type of liver cancer. 30 patients diagnosed as free of HCC received a daily oral dose of 45mg of menatetrenone, 29 did not. The cumulative recurrence rates in the menatetrenone group were 12.5% at 12 months, 39.0% at 24 months, and 64.3% at 36 months. The corresponding recurrence rates in the control group were 55.2, 83.2, and 91.6%, respectively: striking results, to say the least.

"A number of studies have shown that K2 acts as a kind of enabler of other minerals in the body." 

“The current study findings suggested that menatetrenone may have a suppressive effect on recurrence of HCC and a beneficial effect on survival, although a larger, placebo-controlled trial will be required to prove these effects,” the study concluded.

A similar study was carried out by the Department of Gastroenterological Surgery at Dokkyo Medical University and published in 2012. Between January 2005 and September 2009, 101 patients who had recovered from HCC were divided into two groups, one which was to receive 45μg of menatetrenone a day, another which was not. During the observation period, recurrence was observed in 33 patients in the non-MNT group and in 28 patients of the MNT group, less impressive than the 2006 trial but still significant.

"The positive results emerging from some of these trials have set the supplement market abuzz." 

“MNT has a moderately suppressive effect on HCC recurrence after hepatectomy, especially in patients with a normal preoperative DCP level,” the researchers concluded.

There is also some anecdotal evidence to suggest those looking to build muscle have had success using K2 supplements as part of their regime. However, there is currently no scientific research that can support those claims.

Cautious optimism required

The positive results emerging from some of these trials have set the supplement market abuzz, with a handful of K2 specialists emerging and jockeying for position in this relatively new area. In 2013, the market research firm Mintel reported that new food, drink, vitamin and supplement product launches containing K2 had nearly doubled between 2008 and 2012, far eclipsing the growth of K1. That said, according to the same piece of research, only 1% of all food, drink, vitamin and supplement launches during that period were enriched with vitamin K and, of those that were, only 4% contained K2, showing that this strong growth is coming from a very low base.

There is undoubtedly reason for optimism about the potential of K2, with growing numbers of studies suggesting applications beyond what has been realised so far. But more evidence will be needed until it becomes standard for dietetics associations to recommend K2 for improving bone density and more still before its cardiovascular benefits are fully endorsed.

In addition, according to Ursula Philpot, a dietician, senior lecturer at Leeds Metropolitan University and spokesperson for the BDA, most people get sufficient K2 through their diets and the natural production of their intestinal bacteria. For this reason, it is likely that while K2 may be recommended to certain special groups, such as postmenopausal women, the elderly or malnourished, the majority of people have sufficient amounts already.

“There are no trials looking at supplementing vitamin K and D, and seeing if people’s outcomes improve [with regard to calcification of the arteries],” she says. “Yes, possibly it could be helpful. It certainly plays a role in things like the immune system and the formation of bones, but at the moment we don’t have any studies to show that it improves outcomes.”