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Postmenopausal hormone replacement therapy modifies skeletal muscle composition and function: a study with monozygotic twin pairs

¹Department of Health Sciences and ²Finnish Centre for Interdisciplinary Gerontology, University of Jyväskylä, Jyväskylä and ³Department of Medical Rehabilitation, Oulu University Hospital and Institute of Health Sciences, University of Oulu, Oulu, Finland; ⁴Department of Pediatrics, Sahlgrenska Academy at University of Gothenburg, Gothenburg, Sweden; and ⁵HUSLAB, Helsinki University Central Hospital, Helsinki, ⁶Central Finland Central Hospital, Jyväskylä, and ⁷Department of Public Health and Institute for Molecular Medicine, University of Helsinki and ⁸Department of Mental Health and Alcohol Research, National Public Health Institute, Helsinki, Finland

Submitted 20 November 2008 ; accepted in final form 23 February 2009

We investigated whether long-term hormone replacement therapy (HRT) is associated with mobility and lower limb muscle performance and composition in postmenopausal women. Fifteen 54- to 62-yr-old monozygotic female twin pairs discordant for HRT were recruited from the Finnish Twin Cohort. Habitual (HWS) and maximal (MWS) walking speeds over 10 m, thigh muscle composition, lower body muscle power assessed as vertical jumping height, and maximal isometric hand grip and knee extension strengths were measured. Intrapair differences (IPD%) with 95% confidence intervals (CI) were calculated. The mean duration of HRT use was 6.9 ± 4.1 yr. MWS was on average 7% (0.9 to 13.1%, P = 0.019) and muscle power 16% (–0.8 to 32.8%, P = 0.023) greater in HRT users than in their cotwins. Thigh muscle cross-sectional area tended to be larger (IPD% = 6%, 95% CI: –0.07 to 12.1%, P = 0.065), relative muscle area greater (IPD% = 8%, CI: 0.8 to 15.0%, P = 0.047), and relative fat area smaller (IPD% = –5%, CI: –11.3 to 1.2%, P = 0.047) in HRT users than in their sisters. There were no significant differences in maximal isometric strengths or HWS between users and nonusers. Subgroup analyses revealed that estrogen-containing therapies (11 pairs) significantly decreased total body and thigh fat content, whereas tibolone (4 pairs) tended to increase muscle cross-sectional area. This study showed that long-term HRT was associated with better mobility, greater muscle power, and favorable body and muscle composition among 54- to 62-yr-old women. The results indicate that HRT is a potential agent in preventing muscle weakness and mobility limitation in older women.

aging; menopause; sex hormones; muscle strength; muscle power

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