Prolonged Intake of Dietary Fermented Isoflavone-Rich Soybean Reinforced with Zinc Affects Circulating Bone Biochemical Markers in Aged Individuals

Abstract

Changes in circulating biochemical markers of bone metabolism in aged individuals with the intake of fermented soybean (natto), which was made from isoflavone-rich soybean, supplemented with zinc were investigated. Sixty-three volunteers (31 men and 32 women) were divided into four groups of 15 or 16 male volunteers and 16 or 16 female volunteers, and each group was sequentially given natto (40-g pack) containing two different levels of zinc once a day for 4 or 8 weeks as follows: either regular natto with naturally occuring isoflavone 35.0 mg, zinc 0.8 mg and calcium 51.4 mg or supplemented natto containing isoflavone 35.0 mg, zinc 3.6 mg, and calcium 60.0 mg. As serum bone markers, bone-specific alkaline phosphatase, γ-carboxylated osteocalcin, bone tartrate-resistant acid phosphatase (TRAP), and N-telopeptide of type I collagen were assayed. The intake of regular natto for 4 or 8 weeks in men or women persons caused a significant increase in γ-carboxylated osteocalcin, a marker of bone formation, and a significant decrease in serum bone N-telopeptide of type I collagen, a marker of bone resorption, as compared with the value before intake. Moreover, the intake of zinc-supplemented natto for 8 weeks in men or women caused a significant increase in serum bone-specific alkaline phosphatase activity and γ-carboxylated osteocalcin concentration and a significant decrease in serum bone TRAP activity and N-telopeptide of type I collagen, as compared with the values with the intake of regular natto. This study suggests that the intake of regular natto with isoflavone-rich soybean has a stimulatory effect on bone formation and an inhibitory effect on bone resorption in aged individuals, and that the effect is enhanced by supplementation with zinc.