Fig. 3. Changes in bone density as a function of mission duration.

a–c Effect of space flight duration on changes in bone density (% of pre-flight) in region 2 (upper body, a), region 4 (lower limbs, b), and heel bone of individual astronauts (c) was assessed by meta-regression (left for (a–c)) and subgroup analysis (right for a, b). For meta-regression, black solid line/red bands: inter-study (meta) regression ± 95% confidence (dark red) and prediction (light red) intervals; red lines: intra-study regressions. For subgroup analyses, mission-level changes were pooled by mission duration (<100, 100–200, >200 days) and plotted as a function of average mission duration. Horizontal error bars: range of mission durations within subgroup; vertical error bars: pooled standard errors. Marker sizes are proportional to number of astronauts. d Rate of bone loss for regions 2 (left) and 4 (right): slope coefficients β ± 95% CI for meta regressions for all mission durations (β_inter, black), missions longer than 30 days (β_inter > 30 days, blue), individual heel bone data (β_individual, green), and average intra-study regressions (β_intra, red). For region 2, β_intra = −6 [−21, 9].