Older women with a specific type of oestrogen in their blood could be at increased risk of dementia, research from France suggests.
Some 675 women over the age of 65 took part in the study conducted at the French Institute of Health and Medical Research (INSERM) and none of them exhibited any signs of having the cognitive condition at the start.
Blood samples were taken from each to measure levels of oestrogen and memory and thinking tests were conducted after two and four years.
At the end of the second test, 132 of the women had developed dementia.
Those with high levels of oestradiol, a specific type of oestrogen, were found to be twice has likely to have the condition, while participants who also had diabetes were 14 times more likely.
Dr Simon Ridley, head of research at the charity Alzheimer's Research UK, said that past research has linked diabetes and dementia, but tests to determine the role oestrogen can play has produced "mixed results".
He feels this study is very useful, but believes that many different genetic and environmental factors also play a part in the onset of dementia.
"Understanding the underlying reasons for any changes in hormone levels could be important for shedding light on the biological processes that may be involved in the diseases that cause dementia," he added.
"Researchers are making progress in understanding the causes of these diseases, but investment is crucial to turn that understanding into much-needed treatments."
The study was entitled 'Three-City' and its findings were published in the January 2014 edition of the Neurology journal.
According to the Alzheimer's Society, there are more than 800,000 people living with some form dementia in the UK at present and the number is likely to pass one million by 2021 unless a significant breakthrough in research is made.