Comparison of soft tissue body composition in postmenopausal women with or without hormone replacement therapy considering the influence of reproductive history and lifestyle

Objectives: To examine long-term effects of at least 5 years' conventional hormone replacement therapy (HRT), reproductive history and lifestyle on fat mass and muscle mass in postmenopausal women. Research design and methods: A cross-sectional retrospective approach was used, including 64 healthy women (56-69 years, mean age 63.4 years). Hormone users were compared with age-matched non-users with respect to (a) type of HRT used (oestrogen vs oestrogen plus gestagen vs no hormones), (b) categories of oestrogens used (oestradiol-based oestrogens vs conjugated equine oestrogens vs no oestrogens) and (c) categories of gestagens used (testosterone derivatives vs progesterone derivatives vs no gestagens). Data on hormone use, reproductive history (age at menarche, age at menopause, number of years postmenopausal, number of children) and lifestyle (physical activity level, alcohol consumption, smoking habits) were collected by questionnaires. Body composition was analysed by multiple-frequency bioelectrical impedance analysis, estimating fat mass, fat-free mass and body cell mass as absolute values (FM, FFM, BCM, respectively) and percentages of body weight (% FM, %FFM, %BCM). Results: Analysis of covariance, adjusting body composition variables for body mass index, showed that (a) unopposed oestrogen users, oestrogen plus gestagen users and non-users did not differ significantly in body composition variables, (b) users of oestradiol-based oestrogens had significantly more BCM than oestrogen abstainers (p < 0.05), (c) users of testosterone-based gestagens had more BCM than gestagen abstainers. p = 0.05). Stepwise multiple regression analyses, including HRT-related, reproductive and lifestyle variables, indicated that the duration of HRT (p < 0.05) and physical activity level (p = 0.01) were significant positive predictors of %BCM, whereas the number of children significantly positively predicted FM and %FM (each p < 0.05). No significant associations between fat-free mass and HRT were found. Conclusions: The results suggest that conventional doses of oestrogens and gestagens used in HRT might be a factor in preserving muscle mass after long-term administration. It is recommended that BCM is used instead of FFM as an indicator of muscle mass. Studies relating muscle mass to HRT in postmenopausal women should consider physical activity as a possible confounding variable.