The present invention relates to a composition for accelerating calcium absorption containing a poorly absorbable L-form aldonic acid, a salt thereof, or a poorly absorbable L-form aldonolactone. The invention also relates to a food or beverage containing L-arabonic acid, a salt thereof, or L-arabonolactone. The invention also relates to a process for preparing L-arabono-.gamma.-lactone crystals, characterized by dissolving L-arabonic acid in an organic solvent and crystallizing L-arabono-.gamma.-lactone from the solution. According to the invention, a food or pharmaceutical product effective in the prevention or treatment of osteoporosis can be provided.