Published in the European Journal of Epidemiology , Japanese researchers found a positive link between vitamin K2 and hip fractures and osteoporosis, and suggested a review of the , " dietary reference value of vitamin K from the perspective of osteoporosis would be useful."
The current Japanese reference value is 55mcg for women and 65mcg per day for men.
In the US and Canada it is 120mcg per day for men and 90mcg per day for women.
In France the limit is 65mcg per day for both men and women.
"Since regions which consumed a lot of vitamin K, especially vitamin K2, showed a low incidence of hip fracture, we considered that vitamin K intake, not absorption, of over 300 mcg/day would be helpful to reduce the incidence of hip fracture," the researchers concluded.
Family K The vitamin K family includes the forms phylloquinone (K1) that are typically found in cruciferous vegetables and menaquinone (K2), which are sourced from bacteria.
Studies have shown K2 to be the more important nutrient in regard to bone health.
"Menaquinone-7 (K2) showed a very long half-life time compared to vitamin K1," the researchers wrote.
With this in mind they recommended higher doses in regions like Europe and North America, where vitamin K1 consumption is higher.
The study also investigated vitamin D, calcium and magnesium, which have strong clinical bone health backing, and found when these were adjusted for, vitamin K2 continued to reveal a beneficial effect.
Dietary sources The study assessed population diets in various regions of Japan as well as dietary differences, and found that those regions where certain vitamin K-rich fruits and vegetables were prominent had reduced rates of hip fracture.
"There was also a striking pattern of high intake of vitamin K and low incidence of hip fracture in eastern areas of Japan, with the opposite pattern-a low intake of vegetables rich in vitamin K and a high incidence of hip fracture-in western areas," they wrote.
"These findings lend support to the idea that vitamin K is an important factor explaining regional differences in the incidence of hip fracture."
Natto, a food made from fermented soy beans, was singled out as being a particularly abundant vitamin K source.
K for bones
The researchers recognised that the role of Vitamin K role in assisting bone health is relatively new.
"Calcium, the most studied nutrient in the area of bone health, is known for its effectiveness in retarding bone loss in postmenopausal women," they said.
"Magnesium and vitamin D play important roles in calcium and bone metabolism.
Vitamin K, originally recognised as a factor required for normal blood coagulation, is beginning to receive more attention for its role in bone metabolism."
Due to the ecological nature of the study, a "causal linkage between the incidence of hip fracture and intake of vitamin K" could not be confirmed but the researchers said, "further research using more robust epidemiological methods is warranted."
Estimates suggest that in the absence of primary prevention the number of hip fractures worldwide will increase to approximately 2.6 million by the year 2025, and 4.5 million by the year 2050.
Osteoporosis weakens bone strength which increases the likelihood of hip fracture, a problem that increases with age.