Physical function is critical for mobility and quality of life. A team of researchers, including Dr. Nicole Wright, Associate Professor in the Department of Epidemiology at UAB’s School of Public Health, hypothesized that higher total lean mass is associated with higher physical function, and body fat inversely associated, among postmenopausal women.
Women’s Health Initiative Observational Study participants at Pittsburgh, PA; Birmingham, AL; and Tucson-Phoenix, AZ (1993–1998) completed dual-energy X-ray absorptiometry scans and the Rand SF-36 questionnaire at baseline and 3 y (N = 4526). Associations between quartiles (Q1–4) of lean or fat mass and physical function were tested using linear regression, adjusted for demographics, lifestyle factors, medical history, and scanner serial number. At baseline, participants had a mean ± SD age of 63.4 ± 7.4 y and BMI of 27.4 ± 5.8 kg/m2.
Higher percent lean mass was positively associated with physical function at baseline (Q4, 83.6 ± 0.6 versus Q1, 74.6 ± 0.7; p < 0.001), while fat mass (kg and %) was inversely associated (e.g., Q4, 73.7 ± 0.7 versus Q1, 84.2 ± 0.7 kg; ptrend < 0.001). Physical function had declined across the cohort at 3 y; the highest relative lean mass quartile at baseline conferred a lesser decline in physical function than the lowest (Q4, −3.3 ± 0.6 versus Q1–7.0 ± 0.6; ptrend < 0.001), while the highest fat mass quartile (% and kg) conferred greater decline (ex. Kg Q4, −6.7 ± 0.7 versus Q1–2.8 ± 0.6; ptrend < 0.001). Increased fat mass (≥5%), but not lean mass, was associated with lower physical function at 3 y (p < 0.001).
Though this study relies on the subjective assessment of self-reported physical function from the SF-36 subscale, the subscale is widely used and clinically meaningful. The large sample size in this study is a strength, as is the detailed characterization of the population allowing for statistical adjustment for several factors considered to be associated with physical function in the literature. However, statistical adjustment cannot fully overcome the limitation of observational study in terms of understanding causal relations. The field will be advanced by randomized controlled trials of functional interventions. Detailed body composition and functional measurements, as well as sufficient follow-up to assess meaningful long-term changes in physical function across the menopausal years, are needed to fully characterize the contributions of tissue type and quality in future interventions.
The authors concluded that body composition is associated with self-reported physical function both cross-sectionally and longitudinally. Though lean mass (%) was associated with higher physical function, the consistent associations between fat mass and BMI with poorer physical function among postmenopausal women indicate the need to evaluate overall body habitus when predicting risk, especially in the absence of measures of muscle quality.
Full article: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6066466/