It is to provide a pharmaceutical composition which is different from an existing therapeutic agent of an adult disease, of a biochemical reaction-inhibiting type, and which action mechanism is to improve the basal metabolism, wherein the composition has no side effects, and does not generate drug resistance against adult disease; and a method for preventing / treating an adult disease by using the same. It is to provide a composition for preventing / ameliorating an adult disease such as metabolic syndrome, diabetes, hyperlipidemia, hypertension, impaired liver function, renal failure, adiposity, erectile dysfunction, menopausal disorder, shoulder discomfort, and low back pain, comprising 5-aminolevulinic acid (ALA), its derivative, or salt thereof, preferably comprising ALA, its derivative, or salt thereof, and an iron compound such as sodium ferrous citrate, iron sodium citrate and iron ammonium citrate; a food or food material for preventing / ameliorating an adult disease comprising the composition; and a method for using the composition for preparing an agent for preventing / ameliorating an adult disease.