This invention relates to the use of a fatty acid composition comprising at least (all-Z omega-3)-4,7,10,13,16,19-docosahexaenoic acid (DHA), or derivatives thereof, and (all-Z omega-3)-5,8,11,14,17-eicosapentaenoic acid (EPA), or derivatives thereof for manufacturing of a medicinal product or a food stuff for the treatment and/or prevention of amyloidos-related diseases, such as Alzheimer's disease, as well as treatment/prevention of cognitive dysfunction.