And if you like Japanese food ...
Our body needs vitamin K to produce prothrombin, a protein and clotting factor that is important in blood clotting and bone metabolism, and for regulating blood calcium levels. That is how we usually pigeonhole vitamin K.
However, vitamin K's health benefits have been recently shown  to extend beyond blood and bone health and to benefit chronic low-grade inflammatory diseases such as cardiovascular disease, osteoarthritis, dementia, cognitive impairment, mobility disability, and frailty.
There is also interesting, though not definitive, evidence of a direct correlation between vitamin K levels and cognitive performance. Four human studies reported an association of low vitamin K intake or low blood concentrations of vitamin K with cognitive impairment or Alzheimer's Disease.
Brain equivalent to 11 years younger
This new information is transforming our view of vitamin K from simply maintaining our everyday metabolism being a health-promoting supplement. And even more so, since researchers found that, compared with people who rarely ate leafy greens (a prime source of vitamin K) those who had at least one serving a day showed slower brain aging.
In fact, the difference was equivalent to 11 years of aging!!
Those who consumed one or two servings of foods such as spinach, kale, mustard greens and / or collards daily experienced slower mental deterioration than those who ate no leafy greens at all. The investigators found that certain nutrients including vitamin K, folate and lutein, seemed to largely account for the link between leafy greens and slower brain aging.
This is why demand for vitamin K supplements is growing (especially when derived from marine resources). However, for most of us, our vitamin K sources are our everyday food.
Dietary sources of vitamin K
Vertebrates, including humans, do not synthesise vitamin K and depend on dietary sources to obtain the required daily allowance.
We have to discuss two vitamers* of vitamin K separately. i.e. vitamin K1, and vitamin K2. They each have different food sources, bioavailability, and health benefits.
The dietary sources of vitamin K2 (cheese, milk products and meat) differ greatly from those of K1 (leafy greens and non hydrogenated oils).
Vitamin K1 is a product of the photosynthesis process. Therefore, it is in all photosynthetic organisms, including plants, and algae.
It's important to know that vitamin K storage in our body diminishes rapidly without regular dietary intake.
Sources of vitamin K1 - tried shiso?
The main sources of K1 are green leafy vegetables such as kale, romaine lettuce, broccoli, cabbage, and spinach.
Vegetable oils such as soybean, sunflower, olive, and canola are the next best source.
Lower amounts of K1 can also be found in fruits, cereals, meat, and dairy products.
High levels of K1 can be found in everyday Japanese food items such as in vegetables (perilla - shiso), edible seaweed such as hijiki and wakame and dried nori.
Additionally, different types of vegetable fats and oils such as soybean oil and green powdered tea - widely consumed in Japan - are reported to contain high amounts of K1.
Sources of vitamin K2 - do you like natto?
Vitamin K2 is mainly produced by bacteria.
In fact, animal organs not commonly consumed in the diet (liver, brain, pancreas, or kidney) are good sources of K2. Also, the bacterial flora in our gut produces small amounts of K2.
In the main, we need to eat egg yolks and high-fat dairy products, such as hard cheeses, to get enough K2. Cheese is one of the most important sources and in particular, bacteria-fermented cheese such as Norwegian Jarlsberg cheese and Swiss Emmental cheese.
Another important dietary source of vitamin K2 is fermented plant foods e.g. natto. Natto is a traditional Japanese food made by fermenting cooked soybean. It has a very high concentration of K2.
Synergistic - vitamin K and D, potentially
Some research suggests a synergistic effect of vitamin K combined with vitamin D, particularly for bone health.
However, although the benefits of vitamin D in bone health are well established, high levels of vitamin D can be harmful. On the other hand, there is no documented toxicity or adverse health effect from higher doses of vitamin K.
The recommended daily allowance is 75 micrograms of vitamin K.
Summary - mix and match your foods for a younger brain
With evidence showing vitamin K's preventative role in several highly prevalent low-grade inflammatory diseases, it's time to add enough to our diet.
We can eat a nice mix of green vegetables and eggs, combined with full-fat dairy including, and throw in a selection of your Japanese favourites. And if your taste extends to natto, then it is readily available in small packets from your nearest Asian grocery.
You can't really go wrong by adding leafy greens to your diet. By the way, there is a common misconception that raw vegetables are always better. But some nutrients in leafy greens are better absorbed when eaten with fat like an oil-based salad dressing. (And tomato increases in bioavailability when cooked with oil).
Enjoy your vitamin K.
*A vitamer (/ˈvaɪtəmər/) of a particular vitamin is one of several related compounds that exhibit biological activity against a specific vitamin deficiency. Early research identified vitamins by their ability to cure vitamin-specific deficiency diseases. (Wikipedia)
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