Fish/Fish Oil: Cognitive Benefits

Omega-3 supplements and antioxidants may help with preclinical Alzheimer's disease

Here's more evidence that fish oil supplementation and antioxidants might be beneficial for at least some people facing Alzheimer's disease: A new report published in the July 2015 issue of The FASEB Journal describes the findings of a very small study in which people with mild clinical impairment, such as those in the very early stages of the disease, saw clearance of the hallmark amyloid-beta protein and reduced inflammation in neurological tissues. Although the findings involved just 12 patients over the course of 4 to 17 months, the findings suggest further clinical study of this relatively inexpensive and plentiful supplement should be conducted.

"Prevention of mild cognitive impairment progression is one of the best hopes," said Milan Fiala, M.D., Research Professor at the University of California's Department of Surgery in Los Angeles. "In addition to physical and mental exercises recommended by experts, this study suggests that nutrition is equally important."

To make their discovery, Fiala and colleagues investigated the effects of 4 to 17 months of supplementation with omega-3 fatty acids and antioxidants in 12 patients with minor cognitive impairment, 2 patients with pre-mild cognitive impairment, and 7 patients with Alzheimer disease. They measured the phagocytosis of amyloid-beta 1-42 by flow cytometry and microscopy, the transcription of inflammatory genes by RT-PCR, the production of resolvin D1 by enzyme immunoassay, and the cognitive status by MMSE.

In patients with mild clinical impairment and pre-mild clinical impairment, phagocytosis of amyloid-beta by monocytes increased from 530 to 1306 mean fluorescence intensity units. The increase in patients with Alzheimer's disease was not significant. The lipidic mediator resolvin D1, which stimulates amyloid-beta phagocytosis in vitro, increased in macrophages in 80 percent of patients with mild clinical impairment and pre-mild clinical impairment. The transcription of inflammatory genes' mRNAs was increased in a subgroup of patients with low transcription at baseline, whereas it was not significantly changed in patients with high transcription at baseline.

"We've known for a long time that omega-3 fatty acids and some antioxidants can be beneficial to people with a wide range of health problems, as well as protective for healthy people," said Gerald Weissmann, M.D., Editor-in-Chief of The FASEB Journal. "Now, we know that the effects of these supplements may extend to Alzheimer's disease as well. Although these supplements are considered to be generally safe and are very easy to obtain, full-scale clinical trials are necessary to verify the findings of this research and to identify who might benefit the most."

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Omega-3 fatty acids enhance cognitive flexibility in at-risk older adults

A study of older adults at risk of late-onset Alzheimer's disease found that those who consumed more omega-3 fatty acids did better than their peers on tests of cognitive flexibility -- the ability to efficiently switch between tasks -- and had a bigger anterior cingulate cortex, a brain region known to contribute to cognitive flexibility.

The analysis suggests, but does not prove, that consuming DHA and EPA, two omega-3 fatty acids found in fish, enhanced cognitive flexibility in these adults in part by beefing up the anterior cingulate cortex, the researchers report in the journal Frontiers in Aging Neuroscience.

"Recent research suggests that there is a critical link between nutritional deficiencies and the incidence of both cognitive impairment and degenerative neurological disorders, such as Alzheimer's disease," said University of Illinois neuroscience, psychology, and speech and hearing science professor Aron Barbey, who led the study with M.D./Ph.D. student Marta Zamroziewicz. "Our findings add to the evidence that optimal nutrition helps preserve cognitive function, slow the progression of aging and reduce the incidence of debilitating diseases in healthy aging populations."

The researchers focused on aspects of brain function that are sometimes overlooked in research on aging, Zamroziewicz said. "A lot of work in cognitive aging focuses on memory, but in fact cognitive flexibility and other executive functions have been shown to better predict daily functioning than memory does," she said.

"Executive function" describes processes like planning, reasoning, paying attention, problem solving, impulse control and task switching.

"These functions tend to decline earlier than other cognitive functions in aging," Zamroziewicz said.

The new research built on previous studies that found associations between omega-3 fatty acid consumption, cognitive flexibility and the size of the anterior cingulate cortex.

"There's been some work to show that omega-3 fatty acids benefit cognitive flexibility, and there's also been work showing that cognitive flexibility is linked to this specific brain region, the anterior cingulate. But there's been very little work actually connecting these pieces," Zamroziewicz said.

The new study focused on 40 cognitively healthy older adults between the ages of 65 and 75 who are carriers of a gene variant (APOE e4) that is known to contribute to the risk of developing late-onset Alzheimer's disease.

The researchers tested participants' cognitive flexibility, measured levels of the fatty acids EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid) in their blood, and imaged their brains using MRI. Statistical analyses teased out the relationships between these factors.

"We wanted to confirm that higher omega-3 fatty acids related to better cognitive flexibility, and we did in fact see that," Zamroziewicz said. "We also wanted to confirm that higher omega-3 fatty acids related to higher volume in the anterior cingulate cortex, and we saw that. Finally, we were able to show that higher volume in the anterior cingulate cortex was an intermediary in the relationship between omega-3 fatty acids and cognitive flexibility."

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Fatty acids in fish may shield brain from mercury damage 

New findings from research in the Seychelles provide further evidence that the benefits of fish consumption on prenatal development may offset the risks associated with mercury exposure. In fact, the new study, which appears January 21, 2015 in the American Journal of Clinical Nutrition, suggests that the nutrients found in fish have properties that protect the brain from the potential toxic effects of the chemical. 

Three decades of research in the Seychelles have consistently shown that high levels of fish consumption by pregnant mothers - an average of 12 meals per week - do not produce developmental problems in their children. Researchers have previously equated this phenomenon to a kind of biological horse race, with the developmental benefits of nutrients in fish outpacing the possible harmful effects of mercury also found in fish. However, the new research indicates that this relation is far more complex and that compounds present in fish - specifically polyunsaturated fatty acids (PUFA) - may also actively counteract the damage that mercury causes in the brain. 

"These findings show no overall association between prenatal exposure to mercury through fish consumption and neurodevelopmental outcomes," said Edwin van Wijngaarden, Ph.D., and associate professor in the University of Rochester Department of Public Health Sciences and a co-author of the study. "It is also becoming increasingly clear that the benefits of fish consumption may outweigh, or even mask, any potentially adverse effects of mercury." 

"This research provided us the opportunity to study the role of polyunsaturated fatty acids on development and their potential to augment or counteract the toxic properties of mercury," said Sean Strain, Ph.D., a professor of Human Nutrition at the Ulster University in Northern Ireland and lead author of the study. "The findings indicate that the type of fatty acids a mother consumes during pregnancy may make a difference in terms of their child's future neurological development." 

The new study comes as the U.S. Food and Drug Administration and international agencies are in the process of revisiting fish consumption advisories to better reflect the health benefits of nutrients found in fish. The FDA's current guidance - which recommends that pregnant women limit their consumption of certain fish to twice a week - was established because of the known risk of high level mercury exposure on childhood development.

Mercury is found in the environment as a result of both natural and human (e.g. coal plant emissions) activity. Much of it ends up being deposited in the world's oceans and, as a result, fish harbor the chemical in very small amounts.

This has given rise to concerns that the cumulative impact of prenatal exposure to mercury through fish consumption may have negative health outcomes, despite the fact that that a link between low-level exposure and developmental consequences in children has never been definitively established. 

At the same time, fish are rich in a host of beneficial nutrients, including fatty acids, which are essential to brain development, leading to a long-standing exchange among scientists, environmentalists, and policymakers over the risk vs. benefit of fish consumption. This debate has significant consequences for global health, as billions of people across the world rely on fish as their primary source of protein. 

The Seychelles Child Development Study - a partnership between the University of Rochester Ulster University, and the Republic of Seychelles Ministry of Health and Education - is one of the longest and largest population studies of its kind. The Seychelles, a cluster of islands in the Indian Ocean, has proven to be the ideal location to examine the potential health impact of persistent low-level mercury exposure. The nation's 89,000 residents consume fish at a rate 10 times greater than the populations of the U.S. and Europe. 

The study published today followed more than 1,500 mothers and their children. At 20 months after birth, the children underwent a battery of tests designed to measure their communication skills, behavior, and motor skills. The researchers also collected hair samples from the mothers at the time of their pregnancy to measure the levels of prenatal mercury exposure. 

The researchers found that mercury exposure did not correlate with lower test scores. This finding tracked with the results of previous studies by the group - some of which have followed children in the Seychelles into their 20s - that have also shown no association between fish consumption and subsequent neurological development. 

The researchers also measured the PUFA levels present in the pregnant women and found that the children of mothers with higher levels of fatty acids known as n3 - the kind found in fish - performed better on certain tests. Another common form of PUFA, called n6, comes from other meats and cooking oils and is found in greater abundance in the diets of residents of developed countries. 

The fatty acids in fish (n3) are known to have anti-inflammatory properties, compared to n6, which can promote inflammation. One of the mechanisms by which mercury inflicts its damage is through oxidation and inflammation and this has led the researchers to speculate that not only does n3 provide more benefit in terms of brain development, but that these compounds may also counteract the negative effects of mercury.

This was reflected in the study's findings, which showed that the children of mothers with relatively higher levels of n6 did poorer on tests designed to measure motor skills.

"It appears that relationship between fish nutrients and mercury may be far more complex than previously appreciated," said Philip Davidson, Ph.D., the principal investigator of the Seychelles Child Development Study, a professor emeritus at the University of Rochester, and senior author of the study. "These findings indicate that there may be an optimal balance between the different inflammatory properties of fatty acids that promote fetal development and that these mechanisms warrant further study."

 

Fish oil supplements reduce incidence of cognitive decline, may improve memory function

Rhode Island Hospital researchers have completed a study that found regular use of fish oil supplements (FOS) was associated with a significant reduction in cognitive decline and brain atrophy in older adults. The study examined the relationship between FOS use during the Alzheimer's Disease Neuroimaging Initiative (ADNI) and indicators of cognitive decline. The findings are published in the journal Alzheimer's & Dementia.

"At least one person is diagnosed every minute with Alzheimer's disease (AD) and despite best efforts, we have not yet found a cure for this pervasive and debilitating disease," said principal investigator Lori Daiello, PharmD, of the Alzheimer's Disease and Memory Disorders Center at Rhode Island Hospital. "The field is currently engaged in numerous studies to find better treatments for people suffering with AD; however, researching ways to prevent AD or slow cognitive decline in normal aging is of utmost importance."

In this retrospective study, older adults involved in the ADNI study were assessed with neuropsychological tests and brain magnetic resonance imaging (MRI) every six months. The group included 229 older adults who were cognitively normal; 397 who were diagnosed with mild cognitive impairment; and 193 with AD.

The study found that fish oil supplement use during the study was associated with significantly lower rates of cognitive decline as measured by the Alzheimer's Disease Assessment Scale (ADAS-cog), and the Mini Mental State Exam (MMSE), but this benefit was observed only for the group of participants without dementia at the time of enrollment.

It is estimated that more than 5 million people in the U.S. have Alzheimer's disease. It is the most common form of dementia and is the sixth leading cause of death in the U.S.

Fish Oil Prevents Loss of Brain Cells

The more you consume the omega-3 fatty acids found in fish oils, the less likely you are to lose as many precious brain cells as you age, a new study suggests.

More research is needed, however, to understand both why this happens and how much of the nutrient brings about the most benefit, the researchers said.

"Our findings support the idea that a higher omega-3 status from fish or supplements is good for brain health," said study author James Pottala, an assistant professor in the department of internal medicine at the University of South Dakota's Sanford School of Medicine.

According to the study, which was published online Jan. 22, 2014 in the journal Neurology, the researchers tested levels of omega-3 fatty acids in the red blood cells of more than 1,000 older women. Eight years later, the women had MRI scans that measured their brain volumes. At the time of the scans, the women were an average of 78 years old.

Participants whose omega-3 levels were twice as high had a 0.7 percent higher brain volume. "The results suggest that the effect on brain volume is the equivalent of delaying the normal loss of brain cells that comes with aging by one to two years," Pottala said.

Higher omega-3 levels also were associated with greater volume in the hippocampus, the region of the brain in which the memory-robbing disease Alzheimer's first attacks.

The study offers valuable information, said Dr. Gregory Cole, associate director of the Mary S. Easton Center for Alzheimer's Disease Research at the University of Southern California.

"[The study] has a large number of subjects with an objective measure -- the measure of brain volume," Cole said. "Studies that measure things like [memory and thinking] are not as concrete. People have good days and bad days, but when you measure brain volume you get a pretty repeatable measure."

It's also a plus that the participants are all the same gender, so there is no gender variation in brain size to factor in, Cole said.

The study's findings are intriguing, said Dr. JoAnn Manson, chief of the division of preventive medicine at Brigham and Women's Hospital in Boston. "[But] the results should be interpreted cautiously because it's an observational study and not a randomized clinical trial looking at the relationship between omega-3 intake and changes in brain volume," she said.

Although the study showed an association between omega-3 intake and improved brain health, it didn't necessarily prove a cause-and-effect link.

Manson is the principal investigator in a study involving more than 20,000 adults across the United States looking at whether taking daily dietary supplements of vitamin D or omega-3 fatty acids reduces the risk for certain diseases.

The study involves memory testing as well, Manson said. "We'll have some more information in another two to three years, and I think that will be important to see if increasing supplementation with omega-3s is having a clinical impact on [brain] function," she said.

Cole said clinical trials are the only way to find out if high omega-3 consumption really increases brain volume and reduces the risk for dementia.

"This is pretty believable. This is a solid finding," he said. "The question is: How can you translate this into [effectiveness] in people? Will it really work to protect peoples' brains?"

In the meantime, people who want to boost their omega-3 intake can eat nonfried 'oily' fish such as salmon, herring, tuna and sardines. The American Heart Association recommends eating at least two servings of fish a week.

Omega-3 Protects Brain

According to a new study, high long-chain omega-3 polyunsaturated fatty acid content in blood may lower the risk of small brain infarcts and other brain abnormalities in the elderly. The study was published in Journal of the American Heart Association.

In the Cardiovascular Health Study in the USA, 3,660 people aged 65 and older underwent brain scans to detect so called silent brain infarcts, or small lesions in the brain that can cause loss of thinking skills, dementia and stroke. Scans were performed again five years later on 2,313 of the participants.

Research shows that silent brain infarcts, which are only detected by brain scans, are found in about 20% of otherwise healthy elderly people.

The study found that those who had high long-chain omega-3 polyunsaturated fatty acid content in blood had about 40% lower risk of having small brain infarcts compared to those with low content of these fatty acids in blood. The study also found that people who had high long-chain omega-3 polyunsaturated fatty acid content in blood also had fewer changes in the white matter in their brains.

Previously in this same study population, similar findings were observed when comparing those with high or low intake of fish. High content of long-chain omega-3 polyunsaturated fatty acids in blood is a marker for high intake of fatty fish, so the results from the current study support the beneficial effects of fish consumption on brain health.

Fish oil could help protect from dementia

A Loyola University Chicago Stritch School of Medicine study suggests that omega-3 fish oil might help protect against alcohol-related dementia.

Previous studies have shown that long-term alcohol abuse increases the risk of dementia. The Loyola study found that in the brain cells of rats exposed to high levels of alcohol, a fish oil compound protected against inflammation and cell death.

The study by Michael A. Collins, PhD, and colleagues was reported Sept. 8 at the 14th Congress of the European Society for Biomedical Research on Alcoholism in Warsaw.

In the study, Collins and colleagues exposed cultures of adult rat brain cells to amounts of alcohol equivalent to more than four times the legal limit for driving. These cell cultures were compared with cultures of brain cells exposed to the same high levels of alcohol, plus a compound found in fish oil called omega-3 docosahexaenoic acid (DHA).

Researchers found there was about 90 percent less neuroinflammation and neuronal death in the brain cells exposed to DHA and alcohol than in the cells exposed to alcohol alone.

Further studies are needed to confirm whether fish oil protects against alcohol-related dementia. "Fish oil has the potential of helping preserve brain integrity in abusers," Collins said. "At the very least, it wouldn't hurt them."

But Collins added that best way for an alcohol abuser to protect the brain is, if possible, to quit drinking or cut back to moderate amounts. "We don't want people to think it's okay to take a few fish oil capsules and then continue to go on abusing alcohol."

Fish oil may stall effects of junk food on brain

Data from more than 180 research papers suggests fish oils could minimize the effects that junk food can have on the brain, a review by researchers at the University of Liverpool has shown.

The team at the University's Institute of Ageing and Chronic Disease reviewed research from around the world to see whether there was sufficient data available to suggest that omega-3s had a role to play in aiding weight loss.

Research over the past 10 years has indicated that high-fat diets could disrupt neurogenesis, a process that generates new nerve cells, but diets rich in omega-3s could prevent these negative effects by stimulating the area of the brain that control feeding, learning and memory.

Data from 185 research papers revealed, however, that fish oils do not have a direct impact on this process in these areas of the brain, but are likely to play a significant role in stalling refined sugars and saturated fats' ability to inhibit the brain's control on the body's intake of food.

Dr Lucy Pickavance, from the University's Institute of Ageing and Chronic Disease, explains: "Body weight is influenced by many factors, and some of the most important of these are the nutrients we consume. Excessive intake of certain macronutrients, the refined sugars and saturated fats found in junk food, can lead to weight gain, disrupt metabolism and even affect mental processing.

"These changes can be seen in the brain's structure, including its ability to generate new nerve cells, potentially linking obesity to neurodegenerative diseases. Research, however, has suggested that omega-3 fish oils can reverse or even prevent these effects. We wanted to investigate the literature on this topic to determine whether there is evidence to suggest that omega-3s might aid weight loss by stimulating particular brain processes."

Research papers showed that on high-fat diets hormones that are secreted from body tissues into the circulation after eating, and which normally protect neurons and stimulate their growth, are prevented from passing into the brain by increased circulation of inflammatory molecules and a type of fat called triglycerides.

Molecules that stimulate nerve growth are also reduced, but it appears, in studies with animal models, that omega-3s restore normal function by interfering with the production of these inflammatory molecules, suppressing triglycerides, and returning these nerve growth factors to normal.

Dr Pickavance added: "Fish oils don't appear to have a direct impact on weight loss, but they may take the brakes off the detrimental effects of some of the processes triggered in the brain by high-fat diets. They seem to mimic the effects of calorie restrictive diets and including more oily fish or fish oil supplements in our diets could certainly be a positive step forward for those wanting to improve their general health."

The research was published in the British Journal of Nutrition.

Eating omega 3s and avoiding meat, dairy linked to preserving memory

The largest study to date finds that eating foods that contain omega-3 fatty acids, found in fish, and avoiding saturated fats, meat and dairy foods may be linked to preserving memory and thinking abilities. However, the same association was not found in people with diabetes. The research is published in the April 30, 2013, print issue of Neurology®, the medical journal of the American Academy of Neurology.

"Since there are no definitive treatments for most dementing illnesses, modifiable activities, such as diet, that may delay the onset of symptoms of dementia are very important," said Georgios Tsivgoulis, MD, with the University of Alabama at Birmingham and the University of Athens, Greece. Tsivgoulis is also a member of the American Academy of Neurology.

Data came from the REasons for Geographic and Racial Differences in Stroke (REGARDS) study, a national sample of the general population. For the study, dietary information from 17,478 African-American and Caucasian people with an average age of 64 was reviewed to see how closely they adhered to a Mediterranean diet. They were also given tests that measured memory and thinking abilities over an average of four years. A total of 17 percent of the participants had diabetes. Seven percent of the participants developed impairments in their thinking and memory skills during the study.

The study found that in healthy people, those who more closely followed the Mediterranean diet were 19 percent less likely to develop problems with their thinking and memory skills. There was not a significant difference in declines between African-Americans and Caucasians. However, the Mediterranean diet was not associated with a lower risk of thinking and memory problems in people with diabetes.

"Diet is an important modifiable activity that could help in preserving cognitive functioning in late life," said Tsivgoulis. "However, it is only one of several important lifestyle activities that might play a role in late-life mental functioning. Exercise, avoiding obesity, not smoking cigarettes and taking medications for conditions like diabetes and hypertension are also important."

Omega-3 Intake Heightens Working Memory in Healthy Young Adults

While Omega-3 essential fatty acids—found in foods like wild fish and grass-fed livestock—are necessary for human body functioning, their effects on the working memory of healthy young adults have not been studied until now.

In the first study of its kind, researchers at the University of Pittsburgh have determined that healthy young adults ages 18-25 can improve their working memory even further by increasing their Omega-3 fatty acid intake. Their findings have been published online in PLOS One.

“Before seeing this data, I would have said it was impossible to move young healthy individuals above their cognitive best,” said Bita Moghaddam, project investigator and professor of neuroscience. “We found that members of this population can enhance their working memory performance even further, despite their already being at the top of their cognitive game.”

Led by Rajesh Narendarn, project principal investigator and associate professor of radiology, the Pitt research team sought healthy young men and women from all ethnicities to boost their Omega-3 intake with supplements for six months. They were monitored monthly through phone calls and outpatient procedures.

Before they began taking the supplements, all participants underwent positron emission tomography (PET) imaging, and their blood samples were analyzed. They were then asked to perform a working memory test in which they were shown a series of letters and numbers. The young adults had to keep track of what appeared one, two, and three times prior, known as a simple “n-back test.”

“What was particularly interesting about the presupplementation n-back test was that it correlated positively with plasma Omega-3,” said Moghaddam. “This means that the Omega-3s they were getting from their diet already positively correlated with their working memory.”

After six months of taking Lovaza—an Omega-3 supplement approved by the Federal Drug Administration—the participants were asked to complete this series of outpatient procedures again. It was during this last stage, during the working memory test and blood sampling, that the improved working memory of this population was revealed.

“So many of the previous studies have been done with the elderly or people with medical conditions, leaving this unique population of young adults unaddressed,” said Matthew Muldoon, project coinvestigator and associate professor of medicine at Pitt. “But what about our highest-functioning periods? Can we help the brain achieve its full potential by adapting our healthy behaviors in our young adult life? We found that we absolutely can.”

Although the effects of Omega-3s on young people were a focus, the Pitt team was also hoping to determine the brain mechanism associated with Omega-3 regulation. Previous rodent studies suggested that removing Omega-3 from the diet might reduce dopamine storage (the neurotransmitter associated with mood as well as working memory) and decrease density in the striatal vesicular monoamine transporter type 2 (commonly referred to as VMAT2, a protein associated with decision making). Therefore, the Pitt researchers posited that increasing VMAT2 protein was the mechanism of action that boosted cognitive performance. Unfortunately, PET imaging revealed this was not the case.

“It is really interesting that diets enriched with Omega-3 fatty acid can enhance cognition in highly functional young individuals,” said Narendarn. “Nevertheless, it was a bit disappointing that our imaging studies were unable to clarify the mechanisms by which it enhances working memory.”

Ongoing animal modeling studies in the Moghaddam lab indicate that brain mechanisms that are affected by Omega-3s may be differently influenced in adolescents and young adults than they are in older adults. With this in mind, the Pitt team will continue to evaluate the effect of Omega-3 fatty acids in this younger population to find the mechanism that improves cognition.

Other Pitt researchers involved in the project include William G. Frankle, professor of psychiatry, and Neal S. Mason, research assistant professor of radiology.

Teenage boys who eat fish at least once a week achieve higher intelligence scores

Fifteen-year-old males who ate fish at least once a week displayed higher cognitive skills at the age of 18 than those who it ate it less frequently, according to a study of nearly 4,000 teenagers published in Acta Paediatrica.

Eating fish once a week was enough to increase combined, verbal and visuospatial intelligence scores by an average of six per cent, while eating fish more than once a week increased them by just under 11 per cent.

Swedish researchers compared the responses of 3,972 males who took part in the survey with the cognitive scores recorded in their Swedish Military Conscription records three years later.

"We found a clear link between frequent fish consumption and higher scores when the teenagers ate fish at least once a week" says Professor Kjell Torén from the Sahlgrenska Academy at the University of Gothenburg, one of the senior scientists involved in the study. "When they ate fish more than once a week the improvement almost doubled.

"These findings are significant because the study was carried out between the ages of 15 and 18 when educational achievements can help to shape the rest of a young man's life."

The research team found that:

·      58 per cent of the boys who took part in the study ate fish at least once a week and a further 20 per cent ate fish more than once a week.

·      When male teenagers ate fish more than once a week their combined intelligence scores were on average 12 per cent higher than those who ate fish less than once a week. Teenagers who ate fish once a week scored seven per cent higher.

·      The verbal intelligence scores for teenagers who ate fish more than once a week were on average nine per cent higher than those who ate fish less than once a week. Those who ate fish once a week scored four per cent higher.

·      The same pattern was seen in the visuospatial intelligence scores, with teenagers who ate fish more than once a week scoring on average 11 per cent higher than those who ate fish less than once a week. Those who ate fish once a week scored seven per cent higher.

"A number of studies have already shown that fish can help neurodevelopment in infants, reduce the risk of impaired cognitive function from middle age onwards and benefit babies born to women who ate fish during pregnancy" says Professor Torén.

"However we believe that this is the first large-scale study to explore the effect on adolescents."

The exact mechanism that links fish consumption to improved cognitive performance is still not clear.

"The most widely held theory is that it is the long-chain polyunsaturated fatty acids found in fish that have positive effects on cognitive performance" explains Professor Torén.

"Fish contains both omega-3 and omega-6 fatty acids which are known to accumulate in the brain when the foetus is developing. Other theories have been put forward that highlight their vascular and anti-inflammatory properties and their role in suppressing cytokines, chemicals that can affect the immune system."

In order to isolate the effect of fish consumption on the study subjects, the research team looked at a wide range of variables, including ethnicity, where they lived, their parents' educational level, the teenagers' well-being, how frequently they exercised and their weight.

"Having looked very carefully at the wide range of variables explored by this study it was very clear that there was a significant association between regular fish consumption at 15 and improved cognitive performance at 18" concludes lead author Dr Maria Aberg from the Centre for Brain Repair and Rehabilitation at the University of Gothenburg.

"We also found the same association between fish and intelligence in the teenagers regardless of their parents' level of education."

The researchers are now keen to carry out further research to see if the kind of fish consumed - for example lean fish in fish fingers or fatty fish such as salmon - makes any difference to the results.

"But for the time being it appears that including fish in a diet can make a valuable contribution to cognitive performance in male teenagers" says Dr Aberg.