Weight loss in humans in space.

ABSTRACT

INTRODUCTION: Bodyweight loss during spaceflight has been observed among astronauts since the early space missions. Considerable mission data has been accumulated, including data from female astronauts, on the many Shuttle and International Space Station missions. The purpose of this study was to investigate the association between observed weight loss during spaceflight and potential covariate factors. METHODS: We performed a statistical analysis of the association between bodyweight change and plausible clinical and mission covariates, using data obtained from the NASA Longitudinal Study of Astronaut Health (LSAH). RESULTS: We confirmed that spaceflight is associated with weight change (-2.1 +/- 0.1%, N = 514). Prospective predictors of weight loss included being a first-time astronaut, preflight bodyweight and BMI, routinely performing preflight exercise sessions lasting greater than 1 h, and baseline levels of cholesterol, potassium, and chloride. Severe space motion sickness was significantly associated with greater weight loss. Unexpectedly, a higher number of extravehicular activities per mission protected against weight loss. Mission duration had the strongest association with bodyweight change (-2.4 +/- 0.4% per 100 d in space). DISCUSSION: On average, space missions are associated with cumulative loss of bodyweight over time. Unless effective countermeasures are implemented, significant weight loss will be a likely outcome in a subset of astronauts as mission durations increase. New predictors of intra-mission bodyweight changes and other associated factors are identified.