Dr Gail Greendale led a study of almost 2,500 women in 2009 and concluded that levels of female hormones are the likely cause of memory difficulties just before the menopause begins – a stage known as perimenopausal.
She said: ‘Sixty per cent of women state that they have memory problems during the menopause transition.
‘But the effect of perimenopause on learning seems to be temporary.
‘Our study found that the amount of learning improved back to pre-menopausal levels during the postmenopausal stage.’
The average age of the menopause in Britain is 50, when periods stop and many women develop symptoms such as hot flushes, night sweats and depression.
At this age a woman’s supply of eggs has run out and dwindling oestrogen levels are linked to heart and bone problems.
Dr Greendale’s study tested the verbal memory, working memory and processing speed of 2,362 women before, during and after their transition through menopause.
The study found that repeated testing improved the ability of women to process information during the various stages.
But the improvements during the late perimenopausal stage were only up to 30 per cent as large as tests carried out at an earlier point in the transition.
Then after the menopause the scores began to recover.
Dr Greendale, of the University of California, said the findings suggest that during the early and late perimenopause women do not learn as well as they do during other stages of their lives.
The study also showed that taking oestrogen or progesterone hormones – used in Hormone Replacement Therapy – before menopause helped verbal memory and processing speed.
However, when taken after menopause women showed no improvement in processing or memory scores compared with postmenopausal women not taking HRT.
Dr Greendale said: ‘Our results suggest that the critical period for oestrogen or progersterone’s benefits on the brain may be prior to menopause, but the findings should be interpreted with caution.’
Dr John Stevenson, an HRT expert at London’s Royal Brompton Hospital, said: ‘ Difficulties with memory are very common among women around the time of the menopause.
‘When women discover it’s probably a symptom of the menopause, they are usually very relieved as they feared they might be suffering from Alzheimer’s disease.
‘The study’s suggestion that women spontaneously recover is encouraging, but unfortunately some women report to their doctors they have ongoing problems.’