Is it true that, as an old saying has it, "fish is brain food”?
A great deal of evidence from epidemiological (population) studies suggests that it is.
Although epidemiological studies cannot prove a cause-effect relationship, the sheer number and size of such studies supports the old saying pretty strongly.
And a new review of the evidence bolsters the idea that eating fish routinely may reduce the risk of Alzheimer's disease and other forms of dementia (Wu S et al. 2015).
New evidence review finds fish may help deter dementia
Out of 18 studies that met their quality criteria, the China-based research team analyzed the six best-designed studies, which encompassed 22,402 participants.
In each case, the authors of those six studies had looked for links between fish intake – and estimated omega-3 intake – and the study participants' risk for dementia, including Alzheimer's disease.
After pooling the results of those six studies, the authors’ analysis showed that people who consumed fish frequently were 16 percent less likely to develop any form of dementia.
Better yet, the researchers calculated that eating fish frequently cut the risk of Alzheimer's disease – the most common form of dementia – by more than one-third (36 percent).
Adding weight to that finding, the risk of Alzheimer's disease dropped by 11 percent with every additional 100 grams (3.5 ounces) of fish people ate per week.
Drop in dementia risk did not extend to higher omega-3 intakes
There’s loads of evidence that fish-source omega-3s can protect – or even enhance – brain health and performance.
(See our sidebar, "Fish, omega-3s and brain health: Reports from the news archive”.)
Still, the new evidence review did not link higher estimated intakes of fish-source omega-3s to a significant drop in the risk for Alzheimer's disease or other forms of dementia (Wu S et al. 2015).
This could be because fish provides other nutrients linked to brain health, like vitamin D and selenium ... a key component of antioxidant enzymes deemed critical to brain health.
And it’s possible that the researchers who conducted the six studies included in the evidence review mis-estimated the participants’ omega-3 intakes.
It's hard to ensure accurate estimates of people’s omega-3 intakes based on their reported fish intake … even if study participants are interviewed in person (Arsenault LN et al. 2009).
Prior studies of omega-3s for dementia produced mixed results
Can omega-3 fatty acids alone – as found in fish oil supplements – reduce the risk of dementia?
The results of previous studies suggest that indeed, diets high in omega-3s can deter, delay, or reduce the severity of forms of dementia other than Alzheimer’s disease.
But most of the clinical trials testing omega-3 supplements in patients with established Alzheimer’s disease have not detected significant benefits.
However, most of those trials were rather brief, so longer-term benefits may be possible.
The modest benefits seen in some omega-3 fish oil trials do not seem to apply to the one-quarter of Alzheimer’s patients who carry a gene variation called APOE4 ... or who have other potent risk factors (Huang TL et al. 2005; Cederholm T et al. 2013).
Those other risk factors include the average American’s very high intakes of cheap vegetable oils loaded with omega-6 fatty acids (soy, corn, sunflower, safflower, and cottonseed).
We’ll keep following the research in this realm … so stay tuned!
- Arsenault LN, Matthan N, Scott TM, Dallal G, Lichtenstein AH, Folstein MF, Rosenberg I, Tucker KL. Validity of estimated dietary eicosapentaenoic acid and docosahexaenoic acid intakes determined by interviewer-administered food frequency questionnaire among older adults with mild-to-moderate cognitive impairment or dementia. Am J Epidemiol. 2009 Jul 1;170(1):95-103. doi: 10.1093/aje/kwp089. Epub 2009 May 11.
- Cederholm T, Salem N Jr, Palmblad J. ω-3 fatty acids in the prevention of cognitive decline in humans. Adv Nutr. 2013 Nov 6;4(6):672-6. doi: 10.3945/an.113.004556.
- Chowdhury R, Stevens S, Gorman D, Pan A, Warnakula S, Chowdhury S, Ward H, Johnson L, Crowe F, Hu FB, Franco OH. Association between fish consumption, long chain omega 3 fatty acids, and risk of cerebrovascular disease: systematic review and meta-analysis. BMJ. 2012 Oct 30;345:e6698. doi: 10.1136/bmj.e6698. Review.
- Experimental Biology (EB). Diet Can Predict Cognitive Decline: Preliminary data suggest EPA, DHA remain important nutrients. Accessed at http://experimentalbiology.org/
- Huang TL, Zandi PP, Tucker KL, et al. Benefits of fatty fish on dementia risk are stronger for those without APOE epsilon4. Neurology. 2005 Nov 8;65(9):1409-14
- Scott TM et al. Lower dietary intake of long-chain polyunsaturated fatty acids predict cognitive decline. Presentation Number 124.4. Experimental Biology 2014, Sunday, April 27. Accessed at http://experimentalbiology.org/
- Wu S, Ding Y, Wu F, Li R, Hou J, Mao P. Omega-3 fatty acids intake and risks of dementia and Alzheimer's disease: a meta-analysis. Neurosci Biobehav Rev. 2015 Jan;48:1-9. doi: 10.1016/j.neubiorev.2014.11.008. Epub 2014 Nov 21.