Researchers have suggested that the oestrogen levels in women could provide clues to their increased risk of developing dementia.

A team from the George Institute for Global Health in Australia analysed data on a total of 2,73,240 women without dementia and found that some reproductive events - like an early or late start to menstruation, early menopause and hysterectomy - were linked to a higher risk of the neurological disorder characterised by impairment in memory, thinking and social abilities.

However, the findings, detailed in the journal PLoS Medicine, showed that childbearing events - both pregnancy and abortion - and late menopause were linked with lower risk.

Dementia is fast becoming a global epidemic, currently affecting an estimated 50 million people worldwide. This is projected to triple by 2050 - mainly driven by ageing populations. Rates of dementia and associated deaths are both known to be higher in women than men.

According to lead author Jessica Gong from the Institute, although it appeared reproductive events related to changes in hormone levels in women may be involved in dementia risk, the exact relationship was still unknown.

"While the risk of developing dementia increases with age, we don't yet know whether the higher rates seen in women are simply because they live longer," explained Gong. "But it's possible that female-specific reproductive factors may be able to explain some of the sex differences."

Oestradiol is the most predominant form of oestrogen during reproductive life (from the start of menstruation to menopause) and oestriol is the primary oestrogen during pregnancy. Use of hormones that originate from outside the body, such as oral contraceptives during reproductive years, and hormone replacement therapy (HRT) in later life can also influence oestrogen levels.

Further, the study found that the higher dementia risk linked to early (natural and artificial) menopause was more pronounced in women of lower socioeconomic status. "Social deprivation is likely to be an important determinant of dementia risk as well as other aspects of women's health," Gong said.