What is the largest and longest study ever performed supporting a beneficial effect of consuming DHA omega-3 in Alzheimer disease?

This study was performed by Dr. Morris and colleagues from the Rush Institute for Healthy Aging in Chicago. A total of 815 residents (age 65 - 94 years) who were initially free of Alzheimer disease were followed for an average of 4 years. Those who consumed fish with higher intakes of DHA on a regular basis had a 60% lessened risk of developing Alzheimer disease as compared to those who rarely or never ate fish. No apparent protective effect of EPA was found in this population study.