This is the largest study to examine the effects of HRT since the Women's Health Initiative study was stopped in 2002 after linking HRT to an increased risk of breast cancer and thromboembolism.
The observational study followed 698,098 healthy women aged 51 to 69 from 1995 to 2001. It found that overall HRT did not increase the risk of MI, but that women aged 51-54 who took HRT during the period of the study had a 24 per cent higher risk of suffering an MI.
This risk also depended on the type of HRT used. A continuous combination of oestrogen and progesterone was associated with a 35 per cent increased risk of MI, but oestrogen followed by a combination of oestrogen and progesterone was associated with a reduced risk.
Meanwhile oestrogen cut MI risk by 38 per cent via a skin patch, and by 44 per cent if applied via a vaginal gel.
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