Dietary and Urinary Sulfur Can Predict Changes in Bone Metabolism During Space Flight

Abstract

Mitigating bone loss is critical for space exploration, and diet can play a major role in this effort. Previous studies showed that dietary composition could influence bone resorption during bed rest. In this study we examined the role of dietary intake patterns in bone mineral loss in astronauts during space flight. Crewmembers were asked to consume, for 4 days at a time, prescribed menus with either a low (0.3‐0.6 g/mEq) or high (1.0‐1.3 g/mEq) ratio of animal protein to potassium (APro:K). Menus were developed for each crewmember, and were designed to meet both crew preferences and study constraints. Intakes of energy, total protein, calcium, and sodium were held relatively constant between the 2 diets. The order of the menus was randomized, and crews completed each set (low and high) once before and twice during space flight, for a total of 6 controlled diet sessions. One in‐flight session monitored typical dietary intake. On the last day of each of the 4‐d controlled diet sessions, 24‐h urine samples were collected, along with a fasting blood sample on the morning of the 5th day. As of this writing, data are available from 14 crewmembers. The final 3 subjects' in‐flight samples are awaiting return from the International Space Station via SpaceX Dragon capsule. Preliminary analyses show that urinary excretion of sulfate (normalized to lean body mass) is a significant predictor of urinary bone resorption marker n‐telopeptide (NTX). Dietary sulfate (normalized to lean body mass) is also a significant predictor of urinary NTX. The results from this study will be important to better understand diet and bone interrelationships during space flight as well as on Earth. Funded by the Human Health Countermeasures Element of the NASA Human Research Program.