Women's brains start going downhill in their 50s – a decade earlier than previously believed, scientists have warned.

On average the female mind loses up to 5 per cent of its sharpness between 50 and 60, researchers found.

But they said the drop-off did not seem to be caused by the menopause, noting that there was not a ‘sharp acceleration’ in the decline of mental faculties.

Women's brains start going downhill in their 50s – a decade earlier than previously believed, scientists have warned (file photo)

They also said it is not a warning of dementia but a normal feature of ageing and could be held in check or even reversed.

The findings were based on a study that followed more than 2,000 healthy women, enrolled in their 40s, for ten years after the menopause.

Researchers from the University of California, Los Angeles said earlier findings had underestimated the drop-off in mental sharpness.

In two key areas of mental functioning, processing speed and verbal memory, declines were marked.

Verbal memory declined on average by around 1 per cent every five years, and cognitive processing speed, including speed of perception and reaction, showed a decline of 1 per cent every two years. It was not all bad news – one measure that showed no decline in older women was vocabulary.

The research, published in PLOS ONE, said that up to now ‘declines in cognitive performance have not been consistently documented in those under 60 years of age’.

The declines form part of normal healthy ageing and run parallel to the slowing of physical responses such as reaction time, running speed and metabolic rate.

Researchers from University of California found female minds suffered a decline in processing speed and verbal memory between the ages of 50 and 60 (file photo)

The authors said they did not see a ‘sharp acceleration’ of decline after the transition to menopause. But they said they could not be certain that a fall in oestrogen levels did not have a role to play in mental decline as levels of the hormone tail off in the years before the onset of menopause.

Higher levels of fitness and education have both been found to help prevent cognitive decline. Exercise is thought to increase levels of a brain chemical which helps our brains stay healthy.

And people with more mentally demanding occupations maintain cognitive function for longer according to researchers. Stimulating hobbies are also thought to help slow cognitive ageing – the ‘use it or lose it’ theory.

While it has been widely held that decline sets in at around 60, a study of British civil servants found it began at between 45 and 49. Women’s performance at reasoning tests declined by 3.6 per cent from 45-49 over ten years. Men’s ability fell by 3.5 per cent.