Timing and formulation of HRT determines heart attack risk

The age at which a woman begins taking hormone replacement therapy (HRT), its formulation, and how it is administered has a significant effect on their risk of having a heart attack, suggest the results of the largest observational study of HRT since the Women's Health Initiative (WHI) Study.

Dr Ellen Lokkegaard and colleagues studied data collected from nearly 700,000 Danish women aged 51 to 69 for a total of six years. Results showed that, overall, women currently using HRT were not at any greater risk of heart attack than women who had never used HRT. However, the results did show that HRT users aged between the age of 51 and 54 were 24% more likely to have a heart attack than women of the same age who had never used HRT. The results also showed that women who had begun taking HRT between the age of 51 and 54 and had continued to take it for several years were at increased risk of heart attack. No increase in heart attack risk was observed in long-term use of HRT in older women.

The study also found that the formulation of HRT and its route of administration impacts upon heart attack risk. No increased risk was found with the use of estrogen on its own, but continuous administration of estrogen and progesterone was associated with a 35% increased risk of heart attack compared with women who had never used HRT. However, the use of cyclic combined therapy was found to actually lower heart attack risk. The use of estrogen patches was also found to reduce the risk of heart attack (by 38%), as was the use of gel (by 44%).

Løkkegaard E, Andreasen AH, Jacobsen RK, Nielsen LH, Agger C,Lidegaard Ø.  Hormone therapy and risk of myocardial infarction: a national register study. European Heart Journal. Advance Access published online: September 30, 2008. doi:10.1093/eurheartj/ehn408