Intake of fermented soybean (natto) increases circulating vitamin K2 (menaquinone-7) and γ-carboxylated osteocalcin concentration in normal individuals
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Changes in circulating vitamin K2 (menaquinone-7, MK-7) and γ-carboxylated osteocalcin concentrations in normal individuals with the intake of fermented soybeans (natto) were investigated. Eight male volunteers were given sequentially fermented soybeans (natto) containing three different contents of MK-7 at an interval of 7 days as follows: regular natto including 775 μg/100 g (MK-7 × 1) or reinforced natto containing 1298 μg/100 g (MK-7 × 1.5) or 1765 μg/100 g (MK-7 × 2). Subsequently, it was found that serum MK-7 and γ-carboxylated osteocalcin concentrations were significantly elevated following the start of dietary intake of MK-7 (1298 or 1765 μg/100 g). Serum undercarboxylated osteocalcin concentrations were significantly decreased by dietary MK-7 (1765 μg/100 g) supplementation. Moreover, the changes in serum MK-7 level with the frequency of dietary natto intake were examined in 134 healthy adults (85 men and 39 women) without and with occasional (a few times per month), and frequent (a few times per week) dietary intake of regular natto including MK-7 (775 μg/100 g). Serum MK-7 and γ-carboxylated osteocalcin concentrations in men with the occasional or frequent dietary intake of natto were significantly higher than those without any intake. The present study suggests that intake of fermented soybean (natto) increases serum levels of MK-7 and γ-carboxylated osteocalcin in normal individuals.
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