Eating plenty of salmon, mackerel and sardines prevents Alzheimer’s disease by boosting blood flow to specific areas of the brain, a study shows.
Scientists used a sophisticated scanning technique to illustrate exactly how a diet rich in omega-3 - found in oily fish - helps stave off dementia.
The healthy fat increases blood in brain regions that control memory and learning - both of which are destroyed by the devastating neurological disorder.
Fish has traditionally been described as ‘brain food’ - a claim which was dismissed for decades as an old wives’ tale.
But since the turn of the century a growing body of research has suggested it really does improve mental function.
In particular animal experiments have found omega-3 fatty acids combat rogue proteins known as amyloid and tau that clump and tangle together, respectively, in Alzheimer’s patients.
They also prevent brain inflammation - another major factor behind the cause of dementia.
Now the first study of its kind has shed fresh light on the mechanism behind the phenomenon.
People with high omega-3 levels had more blood flowing into specific areas of the brain, according to the findings published in the Journal of Alzheimer’s Disease.
Overall, the study showed the fats improved brain ‘perfusion’ - the amount of blood in certain areas of the brain - and cognition.
Study leader Professor Daniel Amen, of Amen Clinics in Costa Mesa, California, said: “This is very important research because it shows a correlation between lower omega-3 fatty acid levels and reduced brain blood flow to regions important for learning, memory, depression and dementia.”
The eminent psychiatrist said cases of Alzheimer’s are expected to triple in the coming decades and no cure has been found.
Recently, interest in dietary approaches for prevention of cognitive decline has increased.
His team used an imaging technique called SPECT (single photon emission computed tomography) which actuallys shows what the brain is doing by measuring blood flow.
More familar brain scans such as MRI and PET are more limited in only looking at structure.
Participants were scanned while performing various cognitive tasks and when the images were compared there was a statistically significant link between higher blood flow and Omega-3 Index, respectively.
The latter is a measure of the blood concentration of omega-3 fatty acids EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid) - both of which are found in oily fish.
A large part of the brain is made up of omega-3 fats, making them vital for healthy brain function. In fact 60% of the fats in the brain are omega-3 with DHA being the main one.
The researchers also evaluated psychological health using standard tests and found it was better among those with higher omega-3 levels.
The random sample of 166 participants came from a psychiatric referral clinic for whom Omega-3 Index results were available.
They were categorised into two groups - either the higher or lower half of omega-3 consumption.
SPECT scans were carried out on 128 regions of their brains and each participant completed computer tests that measured their mental skills.
The most striking improvements in those with higher omega-3 intake were seen in areas of the brain involved with memory and learning - which are changed especially by ageing and dementia.
Co-author Prof William Harris, of South Dakota University, said: “Although we have considerable evidence omega-3 levels are associated with better cardiovascular health, the role of the ‘fish oil’ fatty acids in mental health and brain physiology is just beginning to be explored.
“This study opens the door to the possibility that relatively simple dietary changes could favourably impact cognitive function.”
Cardiac SPECT scans can be used to inspect the blood flow through the heart - areas of the heart with poor blood flow will appear dark, while those with good flow will appear light.
But they are also beginning to be used to determine which parts of the brain are affected by dementia by looking for changes to blood flow.
Journal editor Professor George Perry, of Texas University at San Antonio, said: “This study is a major advance in demonstrating the value of nutritional intervention for brain health by using the latest brain imaging,”
Omega-3 fats are essential for healthy brain development both in the womb and in early childhood.
They were found to be so important for early brain development they are now automatically added to baby milk formula and it is recommended that pregnant women eat two servings of fish every week - including at least one oil-rich fish.
Studies have found that the children of mothers who eat fish while pregnant have better social and verbal skills at age eight compared to the children of mothers who never ate fish.
But the benefits of eating fish go beyond the early years. Researchers have found many brain-related conditions may be prevented or even treated by good intakes of omega-3 fats, including problems like dementia.
In the UK about 850,000 people have dementia - a figure set to rise to one million by 2025 and 2 million by 2050.
Dr Rosa Sancho, head of research at Alzheimer’s Research UK, said: “Omega-3 fatty acids play an important role in maintaining a healthy brain.
“This study points to a link between higher levels of omega-3 and certain indicators of brain health, but did not look at any potential long-term benefits against conditions like dementia.
“While some previous studies have drawn a link between diets high in omega-3 and a lower risk of dementia, it is unclear how much this effect might be down to other aspects of a healthy diet.
“Alzheimer’s Research UK is funding research into the effects of omega-3 supplements in people at an increased risk of dementia which we hope will give us a clearer idea of whether this fatty-acid could play a role in keeping people’s brains healthier for longer.
“Foods that are high in omega-3 include oily fish and certain nuts and beans. Diets that include these foods, along with plenty of fruits and vegetables and limited processed or sugary foods, have been linked to a range of health benefits.
“While research continues to unpick factors that can affect dementia risk, the best current evidence suggests that adopting a healthy diet while not smoking, staying mentally and physically active, only drinking in moderation and keeping blood pressure and cholesterol in check, can all play a role in maintain a health brain as we age.”
Doug Brown, director of research at Alzheimer’s Society, said: “In recent years there has been increased interest in whether omega-3 could be beneficial for our brain health.
“This new study suggests omega-3 could be linked to blood flow in certain regions of the brain, but the study didn’t look at whether higher blood flow is actually helpful for people with Alzheimer’s.
“A thorough review last year showed that omega-3 does not improve the symptoms of people with Alzheimer’s.
“There is some evidence that eating fish, which contains omega-3, could help to reduce the risk of developing dementia, but it’s not clear if the omega-3 itself is responsible.
“The best step you can take to lower your risk of dementia is to eat a healthy, balanced diet that includes oily fish, fruit and vegetables and take regular exercise.”