by EBSCO Medical Review Board

Alzheimer disease is a condition that progressively affects the ability to learn, function, and remember. It begins with mild memory lapses and progresses to profound loss of memory and function. The long-chain omega-3 fatty acids found in fish have been thought to reduce the risk of the disease by destroying proteins that can damage memory and thinking.

Researchers wanted to investigate the relation of fish intake to cognitive decline. The study, published in American Journal of Epidemiology, found that consuming more than 4 servings of fish per week was associated with slower decline in episodic memory in older adults. Episodic memory is a person's unique memory of a specific event.

About the study

The prospective cohort study pooled 23,688 participants over age 55 from the French Three-City study and 4 US cohorts from 1992 to 1999. Cognitive score was determined from study testing. Fish intake was estimated by self-reported food frequency questionnaires. Study follow-up ranged from 3.9 to 9.1 years.

The study found that:

  • Participants who ate 2-3 servings of fish a week did not differ in episodic memory when compared to those who ate less than 1 serving per week.
  • Participants who ate 4 or more servings of fish per week (0.018 standard units/year) had significantly improved episodic memory when compared to those who ate less than 1 serving per week. Researchers commented that a change in episodic memory of 0.018 standard units per year was the cognitive equivalent to 4 years of aging.

The change in global cognitive score was not significantly different with 1 serving per week, 2-3 servings per week, or 4 or more servings per week.

How Does This Affect You?

Cohort studies are observational studies. These studies simply observe events as they unfold, but do not interfere or introduce factors that can affect the outcome. This is a large study, which generally increases the reliability of outcome. The study is also consistent with 4 earlier studies that associated fish consumption with a reduced risk for dementia and Alzheimer disease. It is important to note that these benefits were not seen in studies where omega-3 fatty acid came from supplements instead of eating fish.

Consuming fish provides many health benefits and few drawbacks. Some organizations recommend eating fish at least 2 times per week as part of a healthy diet. It is a good source of protein, vitamins, and nutrients. All fish contains omega-3 fatty acids, but they are higher in fish that is fatty, such as salmon, trout, sardines, and canned light tuna. If you have any questions, talk to your doctor about the health benefits of eating fish.


Centers for Disease Control and Prevention 

Alzheimer's Society 


Samieri C, Morris MC, et al. Fish intake, genetic predisposition to alzheimer's disease and decline in global cognition and memory in five cohorts of older persons. Am J Epidemiol. 2017 Oct 19.

Alzheimer dementia. EBSCO DynaMed Plus website. Available at: . Updated March 8, 2018. Accessed March 22, 2018.

Revision Information

  • Reviewer: EBSCO Medical Review Board
  • Review Date: 03/2018