Japanese citrus fruit (sudachi) juice is associated with increased bioavailability of calcium from whole small fish and suppressed bone resorption in rats.

Shirasuboshi (boiled and semi-dried whitebait) is a processed fish food that contains abundant calcium. It is eaten whole and commonly consumed in Japan. In this study, the effect of sudachi (Citrus sudachi) juice on calcium, magnesium and phosphorus bioavailability, and bone metabolism in rats was examined. After 14 d of diets low in calcium and phosphorus, male Sprague-Dawley rats were fed shirasuboshi diets containing dried shirasuboshi powder treated with 20% (S20) or 40% (S40) sudachi juice, or distilled water (C) (0.5% Ca; 0.3% P) for 14 d. The apparent absorptions and retentions of calcium, magnesium and phosphorus from shirasuboshi were determined. Bone formation was calculated by measuring serum osteocalcin, and bone resorption by measuring urinary pyridinoline and deoxypyridinoline. The apparent absorption and retention of calcium and magnesium in the S20 group were significantly higher than in the C and S40 groups. Although serum osteocalcin was not affected by the addition of sudachi juice, the urinary pyridinoline and deoxypyridinoline concentrations in the S40 group were significantly lower than in the C and S20 groups. Our results indicate that sudachi juice added to shirasuboshi was associated with increased calcium bioavailability and suppressed bone resorption in rats.