The first meta-analysis, which was led by Professor Manohar Garg from the University of Newcastle in Australia, pooled data from 25 randomized controlled trials and found that while no effect on global cognitive function was observed, a small yet significant effect on memory was observed in healthy people.
“From a mechanistic point of view, the greater benefit of LCn-3PUFA [long chain omega-3 polyunsaturated fatty acids] for memory could be because of the direct role of DHA, the most abundant LCn-3PUFA in the neuronal membrane, in neurogenesis, synaptogenesis, and myelination in the subgranular zone,” wrote the scientists in Nutrition Reviews.
“DHA may continue to play a part in memory and learning in adulthood because of the existence of adult neural stem cells and the role of these cells in neurogenesis.
“Since the accumulation of DHA is region-specific, this may explain the differences in the benefit conferred by LCn-3PUFA with respect to the cognitive domains evaluated,” they added.
MCI
The second meta-analysis, performed by scientists from Shanxi Medical University in China and published in the European Journal of Clinical Nutrition, pooled data from seven randomized clinical trials involving 213 people receiving omega-3s and 221 receiving placebo.
The data showed that omega-3 supplements may improve cognition in older people with mild cognitive impairment (MCI), compared to placebo.
“Previous studies have discussed the relationship between the levels of n-3 LC-PUFAs supplementation and cognitive function. High doses (0.9–2.5 g/day) of DHA/EPA supplementation improved cognitive function in the elderly; low doses (0.3–0.7 g/day) of DHA/EPA seemed to be not enough to affect cognition in nondemented elderly,” wrote the China-based scientists.
“Bo et al. [Nutrients 2017, 9(1), 54; doi: 10.3390/nu9010054] suggested that low doses of n-3 PUFAs can affect cognitive function in individuals with MCI. There is still no consensus on the n- 3 LC-PUFA dose. Further studies with different DHA/EPA dosages can be made.”
What are the baseline Omega-3 levels?
Commenting independently on the new meta-analyses, Harry Rice, PhD, VP of regulatory & scientific affairs for the Global Organization for EPA and DHA Omega-3s (GOED), told us: “It's interesting that two meta-analyses on mild cognitive impairment were published within weeks of each other.
“While I don't consider the results from either study to be overly compelling, I do think there's enough going on to suggest a benefit, but perhaps more importantly, there are some learnings for others that may be doing this type of research.
“I just want to mention two of them. First, both groups of authors recognized the limitations of the mini mental state examination (MMSE). The MMSE has been treated as the gold standard to screen global cognition in "normal" individuals, but it was designed to screen for dementia. It's simply not the right tool.
“Second, it's essential to measure blood omega-3 LCPUFA levels at baseline and at the end of the study. As with so many outcomes, it seems that the individuals demonstrating the greatest benefit of supplementation are those with low baseline omega-3 LCPUFA levels.
“Without this type of information, it's difficult not only to recruit appropriately, but to analyze the data appropriately. This was recently stressed by the International Society for the Study of Fatty Acids and Lipids (ISSFAL) and needs to be considered for all omega-3 LCPUFA research.”
Sources:
Nutrition Reviews
nuz073, doi: 10.1093/nutrit/nuz073
“Long-chain omega-3 polyunsaturated fatty acids and cognitive decline in non-demented adults: a systematic review and meta-analysis”
Authors: A. Alex, et al.
European Journal of Clinical Nutrition
Published online ahead of print, doi: 10.1038/s41430-019-0544-4
“Effect of n-3 long-chain polyunsaturated fatty acids on mild cognitive impairment: a meta-analysis of randomized clinical trials”
Authos: X. Zhang, et al.