Older people who eat fish or seafood at least once a week are at lower risk of developing dementia, including Alzheimer's disease, according to a study published today.

Researchers who followed the medical history of 1,674 people, who were 68 or older, for up to seven years found a fishy diet appeared to have a protective effect.

The authors suggest, in an article in the British Medical Journal, that the fatty acids in fish oils might reduce inflammation in the brain and play a part in regeneration of nerve cells.

The authors from Bordeaux say that a regular diet of meat did not seem to offer the same protection to the people they studied in southwestern France.

A fishy diet, particularly of oily fish, is already recognised to help lower the risk of suffering a heart attack or stroke and there has been recent evidence that it reduces the danger of women giving birth to premature or low-weight babies. Fish has also traditionally been said to be good for the brain.

The findings suggest older people who eat fish once a week might be at 34% lower risk of developing dementia. They also indicate that a regular diet is associated with consumers who have higher education qualifications.

The Alzheimers' Sociey said yesterday that the latest research supported and underpinned other work over the past 18 months which suggested that middle-aged or older people with high blood pressure or cholesterol levels also had twice of the risk of developing dementia later in life.

Most Britons do not eat enough fish, according to food standards agency recommendations.