The effects of bed rest on cardiometabolic health: A systematic review and meta-analysis.

Horizontal bed rest (HBR) and head-down tilt (HDT) are models of physical inactivity. In this systematic review and meta-analysis, we aimed to quantify changes in cardiometabolic outcomes during HBR and HDT in healthy adults. Following the PRISMA guidelines, we searched PubMed, Scopus, Web of Science and Cochrane Library until 1 October 2025. Included studies recruited healthy adults (≥18 years of age) undergoing ≥2 days of HBR or HDT. A meta-analysis with mean differences (MD) and 95% confidence intervals (CI), using random-effects modelling was conducted. Forty-four studies were included. HBR (≤14 days) reduced fasting glucose (MD, -0.15 mmol/L, P = 0.00033). HBR (≤14 days) and HDT (≤60 days) increased insulin (HBR: MD, 7.07 pmol/L; HDT: MD, 9.65 pmol/L; P < 0.0001). The homeostatic model assessment for insulin resistance was increased under both models (HBR ≤30 days: MD, 0.10, P = 0.0004; HDT ≤60 days: MD, 0.24, P < 0.0001). HDT lowered total cholesterol (MD: -13.89 mg/dL, P = 0.000467); HBR raised triglycerides (MD, 18.96 mg/dL, P < 0.0001), and high-density lipoprotein cholesterol was decreased in both models (HBR ≤14 days: MD, -4.53 mg/dL, P = 0.000608; HDT ≤60 days: MD, -6.89; P < 0.0001). C-Reactive protein was elevated in HBR (MD, 1.57; P < 0.0001), and tumour necrosis factor alpha was elevated in both (HBR ≤14 days: MD, 1.33, P < 0.0001; HDT ≤21 days: MD, 0.40; P = 0.00643). In conclusion, HBR and HDT induce model- and duration-specific changes in glucose metabolism and lipid profiles. Interventions that could mitigate these effects may be warranted.