New York, Oct 11 (IANS) Decline in oestrogen levels in women during menopause causes metabolic changes in their brain that may increase the risk of Alzheimer's disease in them, researchers said. This finding on the primary female sex hormone could help in the development of early interventions, they said. According to neuroscientists, depleting levels of the hormone cause a decline in a key neuroprotective element in the female brain, which then raises their risk of developing the disease. "Our findings show that the loss of oestrogen in menopause doesn't just diminish fertility. It also means the loss of a key neuroprotective element in the female brain and a higher vulnerability to brain ageing and Alzheimer's disease," said lead author Lisa Mosconi, Associate Professor at the Cornell University in the US. This decline in oestrogen levels also triggers a shift to a "starvation reaction" in brain cells -- a metabolic state that is beneficial in the short-term but can be harmful in the long term. The findings also revealed reduced volumes of grey matter (brain cells) and white matter (nerve fibre bundles) in female brain regions that are strongly affected in Alzheimer's. "We urgently need to address these problems because, currently, 850 million women worldwide are entering or have entered menopause," Mosconi said, in the paper published in the journal PLoS One. Medical attention provided to women in their 40s, well in advance of any endocrine or neurological symptoms may help them avert the disease, the researchers said. "This study suggests there may be a critical window of opportunity, when women are in their 40s and 50s, to detect metabolic signs of higher Alzheimer's risk and apply strategies to reduce that risk," Mosconi said. Women might need antioxidants to protect their brain activity and mitochondria in combination with strategies to maintain oestrogen levels. Exercise and foods that are rich in antioxidants, such as flaxseeds, also may help boost oestrogen production, the researchers said.