By Craig Weatherby
Omega-3 DHA is a key component of human brain cells, and is critical to brain health.
And, judging by the outcomes of epidemiological studies, dietary DHA appears to promote optimal brain health.
Such studies that rely on diet questionnaires to gauge older people’s estimated fish intakes consistently link higher intakes to better cognitive health.
But epidemiological studies that compare older people’s’ estimated omega-3 intakes to their cognitive outcomes are less consistently positive.
Importantly, the best epidemiological studies – which compare healthy older people’s actual omega-3 blood levels to their cognitive health and performance – consistently detect signs of brain benefits.
Of course, epidemiological studies can't prove that a given food or nutrient produces specific health outcomes. They can only detect stastistically significant links (correlations) between diet factors and health.
Omega-3 DHA: critical to the human brain
Of the two major omega-3s (EPA and DHA) found in human cells, DHA is by far the most critical to brain functioning … in fact, DHA constitutes most of the fatty acids in our fat-rich brains.
The only good food sources of EPA and DHA are fish, shellfish, zooplankton (e.g., krill), and algae … which explains why EPA and DHA are sometimes called “marine” omega-3s.
(People can only convert one to 10 percent of the short-chain omega-3 in plant foods into DHA … hence the far greater value of seafood and/or fish/marine oil supplements.)
Brain levels of DHA decline with age … and researchers suspect that this explains part of many people’s age-related deterioration in brain functions.
Likewise, rodents fed a diet low in omega-3s show brain deficits that are improved by adding DHA to their food … a tactic that also improves memory performance in older mice.
What about controlled clinical trials, the so-called “gold standard” of medical research?
To date, only two randomized, controlled trials have tested the effects of omega-3 pills in older, cognitively healthy people.
One of these trials found benefits in participants carrying the e4 variant (allele) of the ApoE gene – a trait linked to higher risk for Alzheimer’s – but the other found no brain benefits.
Earlier this year, scientists from the Alzheimer's Drug Discovery Foundation noted that epidemiological studies indicate a higher risk of cognitive decline in people with low intakes of omega-3s.
But, as they said, “… these populations have not been specifically targeted by RCTs [randomized, controlled trials].” (Dacks PA et al. 2013)
Prompted perhaps by the need for more clarity on the brain effects of omega-3 fish oil, researchers conducted a clinical trial testing fish oil high in omega-3 DHA … with positive results.
Why did they choose to test a fish oil manipulated to contain more DHA than usual? For the answer, see our sidebar, “Omega-3 DHA: critical to the human brain”.
Malaysian trial sees selected brain benefits from omega-3 DHA
The new trial comes from scientists at the respected National University of Malaysia (NUM).
Lai Kuan Lee and his colleagues conducted a randomized, 12-month clinical trial in 35 people aged 60 years or more.
All were of low-to-middle socioeconomic status and healthy. People taking vitamins, omega-3 or ginkgo biloba supplements were ineligible.
Using standard tests for cognitive health, the researchers selected only volunteers whose scores indicated “mild cognitive impairment” or MCI.
MCI is widely considered a transitional phase between normal age-related cognitive declines and the development of dementia.
The participants were divided into two groups:
Fish oil (1.3 g of DHA and 450 mg of EPA).
Placebo (corn oil rich in omega-6 fatty acids but lacking omega-3s)
Compared with the control group, those in the fish oil group were a bit older (66 vs. 64 years) and had higher blood pressure (systolic and diastolic).
Before and after the trial, they underwent tests for neuropsychological performance, depression symptoms, and overall cognitive function.
In addition, blood was drawn at the outset and again after six months and 12 months.
After 12 months, the volunteers in the DHA fish oil group scored significantly better on several brain-function tests, compared with the control group.
In particular, the fish oil group showed significant improvements in memory, measured as the average of their test scores on five individual tests related to memory function.
The fish oil group also showed measurable – but statistically insignificant – gains in “executive function/attention”.
Scores on the tests for MCI and depression did not differ between the two groups, or change over the course of the study.
Importantly, the findings echo the results of an earlier trial testing the effect of DHA supplements on “verbal recognition memory” in healthy older adults with MCI.
The Maylasian team attributed the beneficial effects of DHA on memory to the participants’ being at a very early stage of cognitive impairment.
The positive outcomes stand in contrast to the lack of benefit seen in studies among people with more advanced cognitive impairment.
Some scientists estimate that more than half of individuals with MCI will advance to Alzheimer’s disease within five years, but others see insufficient evidence.
Biochemical markers of Alzheimer’s disease can appear as early as 10 years before symptoms appear. This suggests that brain protection steps – optimal diet, exercise, and mental activity – should begin as early as possible.
Given the high stakes for people and society, we hope that this study will be repeated in a larger study with more participants.
Dacks PA, Shineman DW, Fillit HM. Current evidence for the clinical use of long-chain polyunsaturated n-3 fatty acids to prevent age-related cognitive decline and Alzheimer's disease. J Nutr Health Aging. 2013 Mar;17(3):240-51. doi: 10.1007/s12603-012-0431-3.
Danthiir V, Burns NR, Nettelbeck T, Wilson C, Wittert G. The older people, omega-3, and cognitive health (EPOCH) trial design and methodology: a randomised, double-blind, controlled trial investigating the effect of long-chain omega-3 fatty acids on cognitive ageing and wellbeing in cognitively healthy older adults. Nutr J. 2011 Oct 20;10:117. doi: 10.1186/1475-2891-10-117.
Jack CR Jr, Knopman DS, Jagust WJ, Petersen RC, Weiner MW, Aisen PS, Shaw LM, Vemuri P, Wiste HJ, Weigand SD, Lesnick TG, Pankratz VS, Donohue MC, Trojanowski JQ. Tracking pathophysiological processes in Alzheimer’s disease: an updated hypothetical model of dynamic biomarkers. Lancet Neurol 2013;12:207-216.
Lee LK, Shahar S, Chin AV, Yusoff NA. Docosahexaenoic acid-concentrated fish oil supplementation in subjects with mild cognitive impairment (MCI): a 12-month randomised, double-blind, placebo-controlled trial. Psychopharmacology (Berl). 2013 Feb;225(3):605-12. doi: 10.1007/s00213-012-2848-0. Epub 2012 Aug 30.