Effect of Vitamin K₂ (Menaquinone-7) and Soybean Isoflavone Supplementation on Serum Undercarboxylated Osteocalcin in Female Long-Distance Runners

Abstract

Fractures of the lower limbs due to fatigue often occur in female long-distance runners. We examined the effect of simultaneous supplementation of 1.35 mg/day of vitamin K₂ (MK-7MK-6) and 72 mg/day of soybean isoflavones for 30 days on bone metabolism in these athletes. Despite the daily intake of 200–400 μg of vitamin K, the vitamin was found to be subclinically deficient in athletes on the basis of γ-carboxyglutamic acid formation of osteocalcin, because supplementation of 1.35 mg/day of vitamin K₂ markedly decreased serum undercarboxylated osteocalcin level by 81%. This suggests that 200 μg/day of vitamin K was not sufficient for γ-carboxylation of osteocalcin. Therefore, supplementation of vitamin K and soybean isoflavones may help reduce the risk of bone fracture in female long-distance runners.