Women who go through the menopause early are more likely to develop Alzheimer's at a younger age, new research suggests. Those who experience the hormonal change in their early 40s develop symptoms of the memory-robbing disease almost two years before other patients. Meanwhile, entering the menopause at around 45 is linked with 15 per cent more dementia-related brain damage, compared to those who do so five years later.The researchers, from the University of California San Francisco, explain that the sex hormone oestrogen - which dramatically declines during the menopause - is known to protect against cognitive decline.Writing in the publication JAMA Neurology, the experts suggest the age at which a woman begins menopause could serve as an 'early marker' of Alzheimer's Disease 'well before cognitive changes become apparent'. For the study, researchers analysed data from more than 2,600 US women with an average age of 78.Around two-thirds of participants experienced a natural, age-related drop in hormones, while the remainder had a surgical menopause - triggered by the removal of the ovaries, for example. The women disclosed the age they became menopausal - 49, on average, - and underwent regular memory and thinking tests. Research has suggested that women are more likely to suffer dementia than men because they lose grey matter as they go through the menopause Everyone experiences dementia differently. Use this checklist to help you make a note of your symptoms before you talk to your GP.Researchers also conducted brain scans in hundreds of the participants in order to track changes over time. Earlier menopause was associated with poorer cognitive outcomes, earlier Alzheimer's onset and more rapid brain shrinkage in later life. Specifically, women who experienced natural menopause at around 45 developed 15 per cent more age-related brain damage over a decade, compared to those who started the menopause at 50, the researchers estimated. The damage affected white matter, which is responsible for carrying messages between brain cells and known to dwindle when dementia develops. Overall, the researchers estimated that women who went through the menopause 10 years earlier than the average age of 49 had around 1.8 fewer years without an Alzheimer's diagnosis than those whose menopause occurred a decade later. Earlier menopause was also linked to a faster decline in episodic memory, the ability to remember events and experiences, as measured by yearly cognitive tests. Surgical menopause was more strongly linked to Alzheimer's risk and memory decline, while earlier natural menopause was more strongly linked to signs of brain ageing on scans.The researchers suggested this could be because when both ovaries are removed, hormone levels drop dramatically, rather than gradually over time.