Salty Life 7 Study: Effect of High Salt Intake on Several Physiological Systems in Immobilisation

Study Overview
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Brief Summary
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The Salty Life 7 study aimed to examine the effect of a high salt (sodium chloride, NaCl) intake on different forms of sodium retention, acid-base balance and bone metabolism and other influenced physiological systems. Because of the fact that astronauts are a vulnerable group in this context, they were of special interest. Astronauts have a high salt intake, probably because of a reduced sense of taste, as well as an increased bone resorption resulting from the lowered mechanical load in space. In which forms sodium could be retained even without fluid retention (osmotically inactive)- contrary to the argumentation of physiological text books - and if the acid-base balance is connected to sodium chloride induced bone loss is examined in a stationary bed rest study with 8 healthy, young, male test subjects. The study consisting of 2 x 21 days is carried out at the German Aerospace Center (DLR). After an adaptation period of 4 days, test subjects are immobilised in 6° head-down tilt bed rest (simulation model for some physiological changes in space) for 14 days during which they received a high (7.7 mmol NaCl/kgBW/d) and a low salt (0.7 mmol NaCl/kgBW/d) intake in cross-over design. The form of sodium retention is investigated by the calculation of daily metabolic sodium-, water- and potassium balances and by changes in body weight. The measurements of bone formation (bAP, PINP, Osteocalcin) markers as well as bone resorption markers (CTX, NTX) supply insight into the influences of a high salt intake on bone metabolism. Blood gas analysis and ph values of 24-h urine are used to gather information about accompanying changes in the acid-base balance. Further physiological systems like energy metabolism and circulation system are also under investigation.

Official Title
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Influence of a High Salt Intake on Sodium Retention, Bone Metabolism and Acid-base Balance in Immobilised Test Subjects

Conditions
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Bone Metabolism, Electrolyte Metabolism, Acid-Base Metabolism, Energy Metabolism, Circulation System

Intervention / Treatment
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* Other: Dietary salt intake


Participation Criteria
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Eligibility Criteria
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Inclusion Criteria: Male Age: 20-35 years Weight: 65±85kg Height:180±10cm. Successfully completed medical & psychological screening Exclusion Criteria: Drugs- and alcohol abuse Hyperlipidemia Obesity Renal diseases Participant of another study in the same time frame and 3 months before starting the study Blood donation within the last three months before starting the study Risk for thrombosis Smoking Diabetes Rheumatism Bone Fracture

Ages Eligible for Study
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Minimum Age: 20 Years
Maximum Age: 35 Years

Sexes Eligible for Study
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Male

Accepts Healthy Volunteers
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Accepts Healthy Volunteers

Study Plan
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How is the study designed?
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Design Details

Primary Purpose: Basic Science
Allocation: Randomized
Intervention Model: Crossover Assignment
Masking: None (Open Label)


Arms and Interventions

| Participant Group/Arm | Intervention/Treatment |
| --- | --- |
| Active Comparator: High salt intake<br> | Other: Dietary salt intake<br> <br> |
| Placebo Comparator: Low salt intake<br> | Other: Dietary salt intake<br> <br> |

What is the study measuring?
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Primary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| To determine the effect of salt intake on bone metabolism in bed rest |  | after 14 days of high and low salt intake | 

Secondary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| To determine the effect of salt intake on acid base metabolism in bed rest |  | after 14 days of high and low salt intake | 
| To determine the effect of salt intake on electrolyte metabolism in bed rest |  | after 14 days of high and low salt intake | 
| To determine the effect of salt intake on the circulation system in bed rest |  | after 14 days of high and low salt intake | 
| To determine the effect of salt intake on energy metabolism in bed rest |  | after 14 days of high and low salt intake | 

 Terms related to the study
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Keywords Provided by Centre Hospitalier Valida
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bone metabolism, salt intake, acid base balance, bed rest