The study, published online on 25 September in the journal Neurology, found no difference in memory and thinking test scores based on levels of omega-3 fatty acids in the blood.
"We looked at the association of blood biomarkers of [omega-3 fatty acids] and measure of cognitive [thinking] function and found no statistically significant association between baseline levels or over time," said the study's lead author, Eric Ammann, a doctoral candidate in the department of epidemiology at the University of Iowa in Iowa City.
Protecting the brain
However, this study's findings run counter to other research that has suggested that omega-3 fatty acids can help protect the ageing brain. A study published in the February 2012 issue of Neurology suggested that middle-aged and elderly people who regularly ate foods rich in omega-3s scored better on tests of visual memory, attention and abstract thinking compared to those who consumed fewer omega-3 foods. The study also found that people who consumed less omega-3s tended to have smaller brain volume overall than those who ate more omega-3 foods.
There are plausible biological mechanisms for why omega-3s might improve brain health, according to background information in the current study. One particular omega-3, called docosahexaenoic acid (DHA), is a structural component of brain tissue, the study authors noted. DHA also has antioxidant and anti-inflammatory properties, which may slow deterioration in the brain.
Ammann's hypothesis going into the study was that omega-3 fatty acids would have a protective effect on thinking and memory in women 65 and older.
Data for the study came from the US Women's Health Initiative study. The researchers included information from more than 2000 women between 65 and 80 years old who had normal thinking and memory at the start of the study.
The women took tests on thinking and memory each year for an average of six years. Blood levels of omega-3s were taken at the start of the study.
Overall, the researchers found no changes in mental function based on the levels of omega-3s in the blood.
There were two tests – fine motor speed and verbal fluency – that showed a slightly significant difference between high levels of omega-3s and low levels of omega-3s, according to the study.
"There were two marginally significant findings between high and low omega-3s, and to some extent those findings align with other studies, but we did look at about 14 different outcomes, so by chance, we would expect to find some on the cusp of statistical significance," explained Ammann.
Incidence of dementia
Ammann said the researchers don't recommend changing your diet based on their findings. "This was a select group of women who were older and healthy at baseline. It's one piece of evidence on the effect of omega-3s and cognitive function," he said. "Our results are looking at the short-term effect of omega-3s. We don't know for someone [who has higher levels] for a longer time, if that would have a more gradual, cumulative effect over time."
Nutritionist Samantha Heller from the Center for Cancer Care at Griffin Hospital in Derby, Connecticut, said, "While this study found no difference between high and low [blood] serum levels of omega-3 fatty acids in memory tests, the researchers did not examine the levels of omega-3 fatty acids and the incidence of dementia in that cohort over time."
Other studies have suggested that omega-3s have numerous benefits, according to Heller. "Evidence suggests that omega-3 fatty acids have many positive health effects including lowering triglycerides [a type of blood fat], reducing the risk of some cancers, affecting mental health, foetal brain and eye development, lowering inflammation and more," she said.
The best way to get omega-3s, she said, is through a healthy diet, rather than through supplements.
"Diets that are replete with whole, healthy foods and very limited in processed, junk and fast food, help provide the body with all the nutrients, including healthy fats like omega-3 fatty acids, it needs," Heller said. "Eating vegetables, whole grains, fruits, legumes, nuts and oils like olive oil, and exercising appears to reduce the risk of cognitive decline and dementias, as well as many chronic diseases."
Learn more about omega-3 fatty acids and your health from the U.S. National Center for Complementary and Alternative Medicine.