There goes my last hope for a food supplement that actually works in old age. The omega-3 fatty acid docosahexaenoic acid is essential for the growth and functional development of the brain in infants and is present in mother’s milk. It has also been proposed that a diet high in omega-3 fatty acids can protect brain health and slow cognitive decline in older persons.
Omega-3 fatty acids are made by marine algae and are concentrated in fish oils. They are believed to be responsible for the health benefits associated with regularly eating fish, such as salmon, tuna, and halibut. Other omega-3 fatty acids are found in plant foods such as flaxseed, walnuts, soy products, and canola and soybean oils. And of course the food supplement industry markets omega-3 supplements.
Studies show no effect of omega-3 supplements on cognitive decline
Now researchers at the National Institutes of Health has concluded that omega-3 supplements do not slow cognitive decline in older persons. In a large double-masked randomised clinical trial they followed 4,000 patients over a five-year period. The patients were divided into four groups with one given a placebo capsule, one given an omega-3 capsule (with 350 mg docosahexaenoic acid and 650 mg eicosapentaenoic acid), one given a capsule with lutein and zeaxanthin and finally one given a capsule with omega-3, lutein and zeaxanthin. The reason for this complex design was to also establish the impact on age-related macular degeneration.
Participants were given cognitive function tests at the beginning of the study to establish a baseline, then at two and four years later. The tests, all validated and used in previous cognitive function studies, included eight parts designed to test immediate and delayed recall, attention and memory, and processing speed. The cognition scores of each subgroup decreased to a similar extent over time, indicating that no combination of nutritional supplements made a difference.
So unfortunately, contrary to popular belief, the researchers didn’t see any benefit of omega-3 supplements in delaying cognitive decline. This is similar to results from a large 2011 study that found that omega-3 supplements did not improve brain health of older patients with preexisting heart disease. However, other studies surveying people’s dietary habits and health have found that regular consumption of fish with omega-3 fatty acids in their ‘natural’ form has benefits for eye, brain and heart health. It may be that the timing of nutrients, or consuming them in a certain dietary pattern, is important.
So a big, black mark against omega-3 food supplements for old age health.
Maybe not the final word
But maybe not so clearcut. Consider that chronic inflammation plays an important role in the development of colorectal cancer, a leading cause of cancer-related death worldwide. Accumulating evidence from animal and in vitro studies indicates that omega-3 fatty acids have potent anti-inflammatory activity and inhibit colorectal carcinogenesis. However, epidemiologic findings on the association between omega-3 fatty acids and colorectal cancer are inconsistent, with even an increased incidence of cancer associated with high omega-3 fatty acid intake reported in some prospective studies.
Now researchers at Harvard have shown that omega-3 fatty acids can have a protective effect against the development of one particular subtype of colorectal cancer. This type of cancer is called microsatellite instable and comprise about 10% to 15% of all colorectal cancers. Complicating the findings, participants with higher intakes of omega-3 fatty acids were more likely to be active, to be regularly taking multivitamins and fish oil supplements, to undergo lower gastrointestinal endoscopy, and to have more frequent consumption of poultry, fruits, and vegetables and less consumption of unprocessed and processed red meat.
Robust conclusions are thus evasive but maybe some glimmer of hope.
And there is more
We have covered the microbiome before. It includes commensal gut bacteria that are generally considered to be friendly, since they can help their host in numerous ways. They can actually help to regulate the immune system, amongst many other beneficial functions that support the host’s health. Remember that inflammation can play a role in colorectal cancer.
In lab-based work on human gut cells, researchers tested whether gut cells respond differently to a commensal bacterium (Lactobacillus gasseri) and two pathogenic bacteria (Escherichia coli and Staphylococcus aureus), and also whether the responses could be altered with omega-3 fatty acids. They found that the lactobacilli increased the secretion of the immune signalling protein TGF-β1 (Transforming Growth Factor β1), but the pathogenic bacteria didn’t. TGF-β1 has an important role in promoting tolerance towards commensal bacteria and also in dampening immune responses following inflammation. When the omega-3 fatty acid eicosapentaenoic acid was added to the cell culture model along with L. gasseri, there was a greater increase in TGF-β1 gene expression.
The results may suggest that there is an interaction between eicosapentaenoic acid and colorectal cell response to a commensal bacterial strain that could possibly be important in cancerogenesis.
Life is complicated
All I can say at this stage is that science can be complicated as is life itself. There is clearly no harm in increasing fish consumption, but you might give omega-3 fatty acid supplements a miss until more convincing results are presented.