Hormone replacement therapy and risk of myocardial infarction: a national register study

Study summary

This observational study, published online in the European Heart Journal on 1 October 2008, looks at the effects of HRT post the Women's Health Initiative trial. The research followed 698,098 healthy Danish women, aged 51-69, between 1995 and 2001.

The study found that, overall, there was no increased risk of heart attacks in current users of HRT compared to women who had never taken it.

Explaining the findings

Heart attack rate in untreated women

The study also found that for the entire group of women in the study aged 50 to 69, the untreated heart attack rate was 17.3 per 10,000 women per year and the continuous combined oestrogen and progesterone rate was 20.7 per 10,000 per year - an absolute increase in risk of 3.4 per 10,000 women per year (approximately 1 in 3,000 absolute increase).  

Heart attack rates in treated women

Tibolone - the Tibolone-treated rate is 12 women per 10,000 per year - an absolute decrease in risk of 5 per 10,000 women per year, or a 29 per cent decrease.

Transdermal - the transdermally -treated rate is 7.7 women per 10,000 per year -  an absolute decrease in risk of 9.6 per 10,000 women per year, or a 55.5 per cent decrease.

Vaginal - the vaginal-treated rate is 10 women per 10,000 per year - an absolute decrease in risk of 7.3 per 10,000 women per year, or a 42 per cent decrease.

Heart attack findings for younger women aged 51-54

The study did find that in younger women (aged 51-54) who were taking HRT during the period of the study, their risk of heart attacks increased from 6 per 10,000 women on no treatment to 8 per 10,000 women on HRT - an absolute increase of risk of 1 in 5,000 per year.

Comment from Professor Henry Burger AO,

The largest previous observational study of the effects of HRT on CVD risk was the American Nurses Health Study, which demonstrated a 30-50 per cent decrease in CVD risk for nurses initiating HRT around the time of menopause, and mostly taking oestrogen alone.

The current large observational study has also reported protective effects of some forms of HRT. Of interest was the reduction in heart disease risk in women taking Tibolone or non-oral forms of oestrogen.

It reports the somewhat unusual finding of a very small increase in heart attack in current users of combined continuous HRT aged 51-54 in Denmark. The absolute risk is 1 in 5,000 per year, meaning that the risk remains very low. It should be noted that the investigators had no information on the menopausal status of the women not on HRT, many of whom may still have been premenopausal. This may have led to a falsely high estimate of risk in the treated women.

Content Updated July 13, 2011