| Abstrakt: |
INTRODUCTION: Research into bone alterations in microgravity has primarily focused on two key aspects: bone mineral density (BMD) and the markers of bone formation and resorption. The aim of this review, therefore, is to determine the effects of natural or simulated microgravity on BMD of different bones, and the biochemical bone markers, along with recommendations for exercise regimes or pharmacotherapies. METHODS: A literature search was carried out using the PubMed database, which yielded 626 results. The following inclusion criteria were applied: (1) either the BMD or the bone formation/resorption markers were reported, (2) the data collected was primary, that is, only original articles, case reports, and case series, (3) the population of the study was humans, (4) the study was conducted in microgravity, either natural or simulated. RESULTS: A total of 54 articles were included in the final systematic review. Twenty-eight of these were observational studies while 26 involved some sort of intervention - particular exercise regimens, strict diets, supplements, or pharmacological agents. Twenty-three studies were conducted during spaceflight, while simulated microgravity was used in 29. Two employed both space- flight and bed rest to derive results. DEXA Scan (n=27) and quantitative-CT (n=12) were commonly used to determine the BMD. Twenty-five studies measured urinary calcium and bone formation/resorption markers to determine bone resorption. The lumbar spine and hip were the most common sites for BMD measurement, and both showed significant losses in microgravity. The radius was largely unaffected. Resistance training was the most commonly employed intervention, but the effectiveness of bisphosphonates (n=7) and supplements (n=3) was also studied. DISCUSSION: Prolonged exposure to microgravity, during spaceflight and bed rest, results in significant losses of BMD in weight-bearing bones, but not in non-weight-bearing areas of the upper limb. The changes in bone markers occur earlier than radiologically detectable BMD loss, but they also recover rapidly once the exposure to microgravity ends, and thus, cannot be surrogate markers during recovery. The current exercise protocols are only partially effective at preventing microgravity-induced osteoporosis, and hence, we recommend more rigorous training regimes combined with pharmacotherapies like bisphosphonates and omega-3 fatty acids. Learning Objectives 1. The audience will understand the impact of microgravity on human bones. 2. The audience will learn about the number of observational and interventional studies conducted on human bones in microgravity. 3. The audience will understand the types of bones involved and the interventions aimed at preventing bone density loss. [ABSTRACT FROM AUTHOR] |
