Lean mass influences overnight changes in hydration, blood pressure and strength in community-dwelling older women

We evaluated the hypothesis that greater lean mass promotes better overnight hydration, improved postural blood pressure and greater strength. Thirty women, aged 71 ± 0.9 years (mean ± SE), completed one measurement in a euhydrated state and another the following morning after an overnight fast. Measurements included hydration, lean mass, orthostatic blood pressure and strength. Participants were grouped by fat-free mass index (FFMI), with cut-points defined as low (< 15.0 kg/m(2)) and normal (≥ 15.0 kg/m(2)). Women with normal FFMI had significantly greater hydration (p < 0.01), lean mass (p < 0.001) and upper body strength (p < 0.05), while those with low FFMI had more unstable blood pressure. On day 1, women with low FFMI experienced significant postural systolic blood pressure changes from sitting to standing (-11.3 ± 4.0 mmHg, p < 0.05). On day 2, they experienced significant systolic changes from lying to sitting (-8.0 ± 2.2 mmHg, p < 0.01) and sitting to standing (-14.9 ± 5.5 mmHg, p < 0.05), and diastolic changes from lying to sitting (-8.9 ± 2.8 mmHg, p < 0.05). In conclusion, overnight fluid shifts in older women with low lean mass result in unstable postural blood pressure and loss of strength that increases the risk for early morning falls.