Functional food factors can play a preventive and therapeutic role in several human diseases. The marine alga Sargassum horneri (S. horneri) has restorative effects in several types of metabolic disorders, including osteoporosis, diabetes, inflammatory conditions, and cancer cell growth. Osteoporosis is widely recognized as a major public health problem. Bone loss associated with ageing and diabetic states was prevented through the intake of bioactive compounds from S. horneri water extract in vivo by stimulating osteoblastic bone formation and inhibiting osteoclastic bone resorption in vitro. The intake of S. horneri water extract was found to have preventive effects on diabetic findings with an increase in serum glucose and lipid components. Furthermore, the S. horneri component has been shown to suppress adipogenesis from rat bone marrow cells and inflammatory conditions in vitro. Notably, the growth of bone metastatic human breast cancer MDA-MB-231 cells, which induce bone loss with osteolytic effects, was suppressed through culturing with the S. horneri water extract component in vitro. The S. horneri component, which has a molecular weight of less than 1000, was found to suppress the activation of NF-κB signaling by tumor necrosis factor-α, a cytokine associated with inflammation, in osteoblastic cells and macrophage RAW264.7 cells in vitro, suggesting a molecular mechanism. The bioactive component of S. horneri may play a multifunctional role in the prevention and treatment of metabolic disorders. This review outlines the advanced knowledge of the biological activity of the aqueous extract components of S. horneri and discusses the development of health supplements using this material.