# The effects of spaceflight countermeasures on trabecular bone score (TBS) of the lumbar spine

## TL;DR

This study shows that specific exercise and medication help protect astronauts' bone health during space missions.

## Contribution

The study introduces TBS as a useful supplement to DXA for evaluating spaceflight's impact on bone health.

## Key findings

- ARED + bisphosphonate maintained bone mineral density in astronauts.
- ARED and ARED + bisphosphonate preserved trabecular bone score.
- TBS enhances DXA assessments of bone health changes during spaceflight.

## Abstract

This study evaluated lumbar spine bone mineral density and trabecular bone score in ISS astronauts using DXA under 3 different countermeasure regimes. ARED + bisphosphonate maintained BMD, while both ARED and ARED + bisphosphonate preserved TBS. TBS supplements DXA assessments of spaceflight effects on bone health.

To assess the utility of lumbar spine (LS) bone mineral density (BMD) and trabecular bone score (TBS) from scans using dual x-ray absorptiometry (DXA) performed in astronauts before and after spaceflights aboard the International Space Station (ISS). The influence of mission duration and of inflight countermeasures on changes described by BMD and TBS was also evaluated from longitudinal DXA tests performed postflight.

Preflight and postflight DXA scans, from which BMD and TBS were acquired, were performed from 51 crewmembers: 41 men (mean age ± SD, 48 ± 5, range 37–56 years) and 10 women (mean age ± SD, 44 ± 3 years, range 41–50 years) who flew on missions of ~ 6 months duration. Participants were categorized into three groups: Pre-ARED (advanced resistive exercise device) (n = 24), ARED (n = 20), and ARED + bisphosphonate (alendronate 70 mg/week) (n = 7). Longitudinal DXA scans were obtained from 311 individual astronauts (266 men, 45 women; age range, 41–80 years) from November 1999 to February 2014 to assess trends following spaceflights, categorized as short-duration (less than 1 bone remodeling cycle [BRC]) and long-duration (> 1 BRC).

Only the ARED + bisphosphonate group was not different from preflight BMD (+ 2.8%, p = 0.1). Regarding TBS, both the ARED and ARED + bisphosphonate countermeasure groups were not different from preflight (+ 0.2%, p = 0.7; −1.5%, p = 0.3). Longitudinal trends of TBS and BMD from short-duration missions revealed declining trends in men. In terms of long-duration missions, there tended to be declining trends in spine BMD and TBS when plotted as a function of age.

DXA can detect how various in-flight countermeasures and the length of mission affect the lumbar spine that is enhanced with the addition of TBS.