Studies on the use of vitamin K for the prevention and treatment of osteoperosis are conflicting. However, there has been some pretty good evidence to support the use of vitamin K2 (menaquinone-4 or 7, or MK-4 or MK-7) in conjunction with vitamin D, calcium, and magnesium for the prevention of hip fractures and to help increase bone mineral density. One study on post-menopausal women who are at risk for bone fractures have shown that this combination seems to be the most protective (1). The combination of diet and lifestyle seem to have the greatest effect on bone mineral density (2). Similar research has been included in Japanese cohorts (3), and is continually being investigated in a large-scale trial called JOINT (Japanese osteoporosis intervention trial).
The richest source of vitamin K2 is found in a Japanese food called natto. It is a fermented soy product. Vitamin K2 is derived from a fermentation process. Japanese studies have shown the protective effect of natto, but it is unsure if it is due to the vitamin K2 or the soy isoflavones. (on a side note, it is important to understand the difference between fermented and unfermented/processed soy foods. The latter has no « natural » protective health benefits apart from being fortified with vitamins and minerals, and these include soya milk, cheese, yoghurt, etc. while the fermented soya is what has been shown to have the protective phytoestrogens for bone health and its use for the protection of estrogen-related cancers). Another source of vitamin K2 is found in curd cheese. Synthetic forms can be manufactured and bought, and recently olive oil has been fortified with vitamin K2 (MK-7).
Osteocalcin, the protein responsible for getting calcium « in » the bone, is a vitamin K dependent protein. Osteocalcin is also regulated by factors which include retinoic acid (vitamin A), glucocorticoids (cortisol), estrogen, and 1,25-hydroxy vitamin D.
In addition to the protective effects on bone, vitamin K2 has been implemented in studies as a prevention for the calcification or hardening of arteries with some sucess. It appears as though this form of vitamin K, as opposed to vitamin K1 found in dark leafy green vegetables that is necessary for blood coagulation, may be beneficial for the prevention of cardiovascular complications. Cardiovascular complications, or coronary artery disease, may be associated with high blood pressure, diabetes, renal disease, hypothyroidism, and post-menopause. Vitamin K2 has been found to be beneficial in persons with type II diabetes (4). Some research has included the use of vitamin K2 for liver cancer, and recently, for the stimulation of testosterone.
Warfarin therapy, an anti-coagulant, has side effects of calcification of the artieries. Probably because it blocks all vitamin K dependent pathways. Some research has pointed to a beneficial effect of using vitamin K with warfarin. However, because of the narrow therapeutic index of warfarin, it is very important to consult with your doctor first before implementing any dietary or nutritional changes to your diet.
This article is a great one for the biochemical explanation for the use of vitamin D and vitamin K: http://www.altmedrev.com/publications/15/3/199.pdf
For any more questions, ask Dr Mel! Thanks for reading. Hope you get a chance to try some natto!
(1) Je SH et al. 2011. J Korea Med Sci Vitamin K supplement along with vitamin D and calcium reduced serum concentration of undercarboxylated osteocalcin while increasing bone mineral density in Korean post-menopausal women over sixty years old.
(2) Moschonis et al., 2011. J Bone Miner Metab. Possible site-specific effect of an intervention combining nutrition and lifestyle counseling with consumption of fortified dairy products on bone mass: the Post-Menopausal Health Study II.
(3) Fujita et al., 2011. Osteoporos Int. Association between vitamin K intake from fermented soybeans, natto, and bone mineral density in elderly Japanese men: the Fujiwara-kyo osteoporosis risk in men (FORMEN) study
(4) Iwamoto J et al. 2011. Nutr Rev. Bone quality and vitamin K2 in type 2 diabetes: review.