FEATURE: Intelligence endures, but forgetfulness begins at 40

PEOPLE'S mental capacities start to decline when they reach 40, according to new research.

Intelligence remains stable, but routine tasks such as remembering someone's name or a telephone number become more challenging. By your mid-forties you will be up to 15 per cent slower at several functions than you were in your twenties, the research, released at the British Psychological Society conference in London yesterday, found.

More than 2,000 men and women aged between 18 and 87 were studied for the effects of ageing on their mental abilities. They were set tests to assess reaction times, memory for words, pictures and numbers and ability to maintain concentration.

The results show that it becomes more difficult to remember names and faces from the age of 40 onwards. It is also more difficult to concentrate on tasks and make decisions. Professor Keith Wesnes, from Cognitive Drug Research, who led the study, said: "By your forties you are not concentrating as well and you cannot focus and ignore distraction to the same extent as you used to.

"You become slightly forgetful, and might not remember what you walked into a room for, or take a long time to recall someone's name. You're less able to bring things to the front of your mind quickly."

The professor said that speed was more commonly affected than accuracy.

What causes the slowdown is not clear. One theory is that it is linked to an age-related deterioration of the messaging system in the brain.

Dr James Semple, an expert in brain chemistry from Addenbrooke's Hospital, Cambridge, said: "It's probable that for some reason the efficiency of the transmitter system decreases in your forties and fifties."

However, in the world of work, the over-forties could still give younger, more quick-witted colleagues a run for their money because of their experience. "Old dogs have strategies and tricks they can use because they have experience working in the system," Dr Semple said. "Maybe they can't process the information as quickly, but they know the short cuts."

Herbal supplements such as ginkgo could help to speed up the over-forties, according to the research. In one recent trial, a group of middle-aged people showed a 7 per cent mental improvement after taking a combination of ginkgo and ginseng.