Prolonged intake of dietary fermented soybeans (natto) with the reinforced vitamin K2 (menaquinone-7) enhances circulating γ-carboxylated osteocalcin concentration in normal individuals

Abstract

The change in circulating vitamin K2 (menaquinone-7; MK-7) and γ-carboxylated osteocalcin (Gla osteocalcin) concentrations in normal individuals with the intake of fermented soybean (natto) was investeigated. Forty eight volunteers (forty five males and three females) were divided into three groups of sixteen volunteers each (fifteen males and one female), and each group was given sequentially the fermented soybean (natto; 50 g) containing three different contents of MK-7 once a day for 14 d as follows: Either regular natto with 865 μg MK-7/100 g of natto, reinforced natto containing 1295 μg MK-7/100 g, or 1730 μg MK-7/100 g. Serum MK-7 was not found in normal individuals who had not had natto intake. Serum MK-7 and γ-carboxylated osteocalcin concentrations were significantly raised 7, 10, and 14 d after the start of the intake of reinforced natto containing 1295 or 1730 μg MK-7/100 g. However, serum μ-carboxylated osteocalcin levels were not significantly elevated by the intake of regular natto, although serum-MK-7 levels were significantly raised. Moreover, serum γ-carboxylated osteocalcin concentration was significantly elevated 14 d after the intake of natto containing either 1295 or 1730 μg MK-7/100 g, as compared with that of regular natto intake. The present study suggests that the intake of dietary MK-7 in the reinforced natto can stimulate γ-carboxylation of osteocalcin, which plays an important role in bone formation in normal individuals.