Researchers conducted a retrospective cohort study to assess the effects of oestrogen-only and combined HRT on overall and age-specific all-cause mortality in healthy women. The study participants, identified from The Health Improvement Network (THIN) database in the UK, included 105,199 healthy women aged 46 to 65 years at the time of their first HRT prescription and 224,643 age- and general practice-matched controls (non-users).
Besides adjusting for demographic and lifestyle factors, the study also adjusted for type II diabetes, hypertension and it's treatments, coronary heart disease and oophorectomy/hysterectomy status, as well as BMI, smoking and deprivation status.
Overall, the researchers recorded 21,751 deaths over an average of 13.5 years follow-up per participant. Of these, 6,329 occurred among HRT users and 15,422 among non-users.
Risk reduction greater for combined HRT
The risk of overall all-cause mortality in combined HRT users was 9% lower than in non-users (adjusted hazard ratio [HR] 0.91 [95% CI 0.88-0.94]). In contrast, the reduction in risk in women using oestrogen-only HRT was only 1% lower than in non-users (HR 0.99 [95% CI 0.93-1.07]).
When adjusted for age the greatest reduction in risk of all-cause mortality among combined HRT users was seen in those aged 51 to 55 years at first treatment (13% versus 2%, 12% and 8% among participants aged 46 to 50, 56 to 60 and 61 to 65 years at first treatment, respectively). Among oestrogen-only HRT users there were no significant differences between users and non-users (HRs 1.01, 1.03, 0.98 and 0.93 in participants aged 46 to 50, 51 to 55, 56 to 60 and 61 to 65 years at first treatment, respectively).
Commenting on the findings, Dr Nick Steel, Clinical Professor in Public Health at Norwich Medical School and one of the study authors, said that the the fact that combined HRT was associated with an overall lower risk of death and oestrogen-only HRT was not linked to an increased risk of death was exciting. "HRT use has been controversial for many years, as it offers symptomatic relief to many women but there have been conflicting reports about the long-term risk of breast cancer, as well as possible benefits to cardiovascular health. UK primary care data has enabled long term follow up of thousands of women in the UK, comparing the overall risk of death over many years for those using HRT with those not using it."