Abstract: Methods and compositions for treating and preventing osteoporosis are disclosed. Osteoporosis is prevented and treated by administering an effective amount of a composition to a patient. The composition may be prepared from New Zealand green-lipped mussel (Perna canaliculus) and may comprise one or more proteins, amino acids, minerals, sterol esters, sterols, polar lipids, triglycerides, fats, lipids, fatty acids, and polyunsaturated fatty acids (PUFAs) derived from the mussel. The active ingredients in the composition include one or more of an octadecatetraenoic acid (SDA), an eicosatetraenoic acid (ETA), an eicosapentaenoic acid (EPA), and a docosahexaenoic acid (DHA).