True or false: eating more green leafy vegetables will help prevent osteoporosis by providing vitamin K.

It’s false. If this surprises you it may be because misleading information about this important nutrient is as widespread as its deficiency in Canadian diets.

Vitamin K is not a single nutrient, but a group of fat-soluble vitamins. Just as we differentiate between B vitamins, any accurate statement about the benefits and dietary sources of “vitamin K” should distinguish the specific type of vitamin K. Fortunately, there are only two members of the K family that have significant health benefits, but the difference between them is vast. Confuse the two – as scientists did for six decades - and you may end up missing out.

Since their discovery in the 1930’s, researchers assumed that K₁ (phylloquinone) and K₂ (menaquinone) were merely different forms of the same nutrient. Only in 1997 was it recognized that vitamin K₂’s major impact is on calcium metabolism, not blood clotting like K₁. Even more recent studies show that clinically significant vitamin K₂ deficiency is common, which is not the case for K₁.

Unlike other fat-soluble vitamins, the body doesn’t store any type of vitamin K in appreciable amounts. However, due to its critical role in blood clotting, vitamin K₁ levels are tightly controlled by a mechanism that minimizes the dietary requirement of this form of the nutrient. Even if you don’t have a single serving of greens for weeks the vitamin K cycle allows a small amount of K₁ to be reused many times, thus preventing a deficiency.

No such system exists to protect against a diet that’s lacking in K₂, however, and the effects of a long-term deficit are insidious: osteoporosis, atherosclerosis and dental cavities. Unlike some species, humans don’t convert dietary K₁ to K₂ in sufficient amounts to prevent a deficiency. We must rely on our nutrition to provide K₂, making it an essential nutrient.

Dietary sources of K₂ seem common enough: egg yolks, butter, liver. However, to have a worthwhile amount of K₂, the animals providing those foods need to be fed on grass instead of grain. The fermented, Japanese soybean food nattô is an excellent source of vitamin K₂, although finding it is challenging and acquiring a taste for the stuff even more so. Look for a natto-based K₂ supplement that provides 120 mcg per daily dose.

	K1	K2
Physiological action	Blood clotting	Calcium metabolism
Food sources	Green leafy vegetables	Nattô, egg yolk, liver, grass-fed animal fats
Deficiency	Uncommon – leads to bleeding disorder	Common – manifests as osteoporosis, arterial plaques, dental cavities

References:

Cranenburg EC, et.al., Vitamin K: The coagulation vitamin that became omnipotent. Thromb Haemost. 2007 Jul;98(1):120-5.

Geleijnse JM, et al. Dietary Intake of Menaquinone Is Associated with a Reduced Risk of Coronary Heart Disease: The Rotterdam Study. J Nutr 2004;134: 3100-3105.

Masterjohn, Chris, On the Trail of the Elusive X-Factor. Wise Traditions 2007;8(1)14-32

Kate Rhéaume-Bleue, ND, first wrote about vitamin K for alive in 2008. Dr. Rhéaume-Bleue lectures across Canada and regularly appears on TV and radio as a natural health expert.

Source: alive Web Exclusive, March 2010