Researchers have discovered why older women are more likely to suffer from cardiovascular disease than older men.
Cardiovascular disease is a general term for conditions affecting the heart or blood vessels and previous studies have shown differences between the sexes in the age at which they occur.
Coronary heart disease, for example, develops on average seven to 10 years later in women compared with men, occurring three to four times more often in men than in women below the age of 60 years.
But after the age of 75 most patients are women.
The new study, carried out at Germanys Charite University Medicine Berlin, looked at healthy hearts to see if there were sex differences in the function of mitochondrial (tiny structures found in cells) and inflammation during ageing.
The research, which is being presented at Frontiers in CardioVascular Biology (FCVB) 2018, a European Society of Cardiology (ESC) congress, found that older women had mitochondrial dysfunction, reduced antioxidant proteins, and increased inflammation.
Heart tissue was obtained from seven women and seven men aged 17 to 40 years, and from eight women and nine men aged 50 to 68 years.
The researchers measured levels of proteins involved in inflammation and in the function of the mitochondria.
They found the levels of Sirt1, a protein which is important for the function of the mitochondria, were higher in young women compared to young men.
In the older hearts, Sirt1 levels had decreased in women but not in men.
Expression of superoxide dismutase 2, an antioxidant protein in the mitochondria, was higher in young females than males but the difference was no longer present with age.
In addition the expression of catalase, an enzyme that protects cells from oxidative damage, was higher in young females than males but again the difference was lost with age.
Dr Maria Luisa Barcena de Arellano said: "Our study provides a molecular explanation for the increased incidence of cardiovascular diseases in older women.
"We found that the hearts of older women have reduced expression of antioxidant proteins and proteins that are important for mitochondrial function.
"This may lead to the increased inflammation we observed in older women. Inflammation is known to contribute to cardiovascular disease."
She said that in young women, oestrogen may protect or improve the function of the mitochondria and keep inflammation down, but it is thought the fall in oestrogen during menopause contributes to mitochondrial dysfunction.
Hormone replacement therapy is taken by some women to boost oestrogen levels and reduce the risk of heart disease, but it may not be appropriate for everyone, she said.
Dr Barcena de Arellano added: "Our study suggests that a new drug could be developed which increases the expression of mitochondrial proteins.
"This could improve mitochondrial function, reduce inflammation, and help to prevent cardiovascular disease in older women."