---
title: "In missions longer than 30 days, spaceflight bone-mineral-density loss runs about 0.8% per month at the lower limbs"
type: "claim"
status: "seedling"
audit_status: "capture-verified (PMC full text was fetched and quoted directly at capture; independent headless re-check blocked — WebFetch requires interactive permission unavailable in this pipeline)"
source_url: "https://pmc.ncbi.nlm.nih.gov/articles/PMC7200725/"
source_title: "A systematic review and meta-analysis of bone loss in space travelers"
source_author: "Stavnichuk M, Mikolajewicz N, Corlett T, Morris M, Komarova SV"
source_date: "2020-05-05T00:00:00.000Z"
source_quote: "−0.8% [−1.1, −0.5] per month"
source_tier: 1
provenance: "Promotion from 10-inbox/raw/2026-07-12-does-head-down-bed-rest-quantitatively-track-spaceflight.md, 2026-07-12 (headless)"
writer_model: "claude-opus-4-8"
origin: "batch"
derived_from: "10-inbox/raw/2026-07-12-does-head-down-bed-rest-quantitatively-track-spaceflight.md"
date_created: "2026-07-12T00:00:00.000Z"
tags: ["space-medicine","aerospace-physiology","bone-density","calcium-loss","meta-analysis"]
---


A systematic review and meta-analysis of spaceflight-only bone-mineral-density
(BMD) data, pooling multiple missions and skeletal sites, reports that on
missions longer than 30 days the lower limbs lose "−0.8% [−1.1, −0.5] per
month," while the upper limbs and thorax barely change at "−0.1% [−0.2, 0.0]
per month." Expressed as total post-flight loss, the lumbar spine and pelvis
fall by "−6.2% [−6.7, −5.6]." The strongly weight-bearing lower skeleton
demineralizes; the non-weight-bearing upper skeleton essentially does not — a
regional gradient consistent with mechanical unloading as the driver.

These are the spaceflight-side reference figures against which the ground
analog is judged. The meta-analysis is spaceflight-only and, as the capture
verified directly, does not itself run a statistical bed-rest-versus-flight
comparison in its main text; it supplies the orbital numbers that the bed-rest
figures in
[[claim-bed-rest-bmd-loss-about-one-percent-per-month-hip-pelvis-heel]] and
[[claim-bed-rest-bone-turnover-markers-run-half-spaceflight-magnitude]] are
paired against. That pairing is the substance of
[[claim-bed-rest-under-runs-spaceflight-bone-loss-depends-on-readout]]. The
whole comparison traces back to the in-flight concern recorded in
[[claim-gemini-nutrition-report-embeds-a-bone-demineralization-concern]] and the
ground program of
[[claim-pauline-beery-mack-became-nasas-bone-density-pi-at-seventy]].

> [!note] Seek's commentary:
> The −0.8%/month lower-limb rate is the number most people quote as "the"
> spaceflight bone-loss figure, but it is a pooled estimate across missions and
> sites with wide confidence intervals, and the site-by-site spread (−0.8% legs
> vs −0.1% arms) matters more than the headline. Averaging over the skeleton
> would blur exactly the regional signal that makes the mechanism legible.
> — Seek