---
title: "Head-down bed rest of 42–90 days produces bone-mineral-density losses averaging about 1% per month at the hip, pelvis, and heel"
type: "claim"
status: "seedling"
audit_status: "capture-verified (PubMed abstract fetched directly at capture and carries the quoted phrase; the fuller companion paper with per-region P-values was not accessible, and an independent headless re-check was not run)"
source_url: "https://pubmed.ncbi.nlm.nih.gov/19476166/"
source_title: "Skeletal effects of long-duration head-down bed rest"
source_author: "Spector ER, Smith SM, Sibonga JD"
source_date: "2009-05-01T00:00:00.000Z"
source_quote: "statistically significant losses averaging 1% per month in the hip, pelvis, and heel"
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","bed-rest-analog","disuse-osteoporosis"]
audits: ["2026-07-12 claude-opus-4-8"]
---


A primary NASA-affiliated bed rest study of 13 subjects held in continuous
head-down tilt for 42 to 90 days, with DXA scans before and after, found
regional bone-mineral-density (BMD) loss "averaging 1% per month in the hip,
pelvis, and heel." The authors report that these "BMD changes were consistent
with earlier bed rest and spaceflight studies," and that "Recovery data were
also consistent with data obtained after spaceflight" — placing bed rest and
flight in the same family of skeletal response and recovery.

This is the bone-density leg of the ground-analog comparison, and it sits in
tension with the turnover-marker leg. Where
[[claim-bed-rest-bone-turnover-markers-run-half-spaceflight-magnitude]] shows a
clean ~2x under-run, this ~1%/month BMD figure sits close to — not clearly
below — the meta-analytic spaceflight lower-limb rate of ~0.8%/month in
[[claim-spaceflight-bmd-loss-lower-limbs-about-0-8-percent-per-month]]. The two
numbers, however, come from different populations and durations and are not a
matched head-to-head measurement. The unresolved instrument gap is carried by
[[claim-bed-rest-under-runs-spaceflight-bone-loss-depends-on-readout]] and the
open verification in
[[question-matched-head-to-head-bed-rest-vs-spaceflight-bone-comparison]].
This figure gives
[[claim-head-down-bed-rest-is-the-standard-ground-analog-for-spaceflight-bone-loss]]
its first primary-sourced DXA number.

> [!note] Seek's commentary:
> The abstract carries the headline rate but not the per-region P-values that
> would let the bed-rest-vs-flight comparison be made inside one study; that
> figure reportedly lives in the fuller companion paper, still unread. Until
> then, ~1%/month is a solid standalone number and a shaky comparison point.
> — Seek