How Do Omega-3 Fatty Acids Affect Brain Health and Cognitive Aging?

The short answer

DHA (docosahexaenoic acid) constitutes approximately 40% of the polyunsaturated fatty acids in the brain and is essential for neuronal membrane fluidity, synaptic function, and neuroprotection. Low DHA levels are associated with faster cognitive decline, smaller brain volume, and higher Alzheimer's risk. Supplementation improves cognitive function in older adults with low baseline DHA levels, but evidence is weaker in those with adequate DHA.

What the evidence actually shows

Yurko-Mauro et al. (2010) in Alzheimer's & Dementia conducted an RCT of DHA supplementation (900 mg/day) in 485 older adults with age-related cognitive decline and found significant improvements in learning and memory after 24 weeks. Tan et al. (2012) in Neurology, using data from the Framingham Heart Study, found that higher red blood cell DHA levels were associated with larger brain volume, larger hippocampal volume, and better cognitive performance. Jiao et al. (2014) in Nutrients conducted a meta-analysis of 9 RCTs and found that omega-3 supplementation significantly improved cognitive function in older adults with mild cognitive impairment but not in those with normal cognition.

"Higher DHA levels were associated with larger brain volume, larger hippocampal volume, and better cognitive performance."

— Tan et al., Neurology 2012

What the major health authorities say

The NIA identifies omega-3 fatty acids as a nutrient of interest for cognitive health and notes that low DHA is associated with cognitive decline. MedlinePlus notes that omega-3 fatty acids are important for brain health and that fatty fish is the best dietary source. The NIA recommends consuming fatty fish at least twice per week as part of a healthy diet for brain health.

Practical implications

The best dietary sources of DHA are fatty fish: salmon (1,800 mg per 85g), mackerel (1,000 mg per 85g), sardines (835 mg per 85g), and herring (940 mg per 85g). For those who do not eat fish, algal oil supplements (the original source of DHA in the food chain) provide DHA without the environmental concerns of fish oil. The evidence for cognitive benefit is strongest in individuals with low baseline DHA levels — those who rarely eat fish. For regular fish consumers, additional supplementation may provide less benefit.

Where reasonable people still disagree

• Whether omega-3 supplementation prevents Alzheimer's disease or only slows cognitive decline in those with mild impairment.
• The optimal ratio of EPA to DHA for cognitive versus cardiovascular benefits.
• Whether algal oil provides equivalent cognitive benefits to fish oil, given differences in the EPA:DHA ratio.