Worried about dementia? Oily fish really is the best protection

DIETS lacking an essential nutrient found in oily fish may hasten brain shrinkage and mental decline, a study has found.

Brain scans carried out on 1,575 people with an average age of 67 showed a greater rate of brain shrinkage in those who lacked docosahexaenoic acid (DHA).

DHA is an omega-3 fatty acid that is thought to help nerve cells communicate with each other. The richest source of the nutrient is oily fish, such as herring, mackerel and sardines.

Dr Zaldy Tan, from the University of California atLos Angeles, who led the US research reported in the journal Neurology, said: "People with lower blood levels of omega-3 fatty acids had lower brain volumes that were equivalent to about two years of structural brain ageing."

The study involved magnetic resonance imaging (MRI) brain scans and tests for mental function and omega-3 fatty acids in red blood cells.

Participants whose DHA levels were among the bottom 25pc had smaller brains than those with higher DHA levels.

Low levels of all omega-3 fatty acids were also associated with poor test scores for visual memory, problem solving, multi-tasking and abstract thinking.

Dr Marie Janson, from the British charity Alzheimer's Research UK, said: "There has been a lot of research into the effects of omega-3, and this study will add to that debate.

"One strength of this study is that it used blood samples to measure people's dietary intake of omega-3, rather than relying on answers to questionnaires to assess the link between omega-3 and cognition. However, this research does not tell us whether the people studied got worse or better over time.

"We would need to see large-scale, long-term studies before we can know whether a diet high in omega-3 can protect against dementia, and people shouldn't fill their freezers with oily fish just yet. The best evidence for reducing your risk of dementia is to eat a healthy, balanced diet, take regular exercise and keep your blood pressure and cholesterol in check."

More than 800,000 people in the UK suffer from dementia, with the majority affected by Alzheimer's disease.

- John von Radowitz