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Trial registered on ANZCTR

Registration number
Ethics application status
Date submitted
Date registered
Date last updated
Type of registration
Prospectively registered

Titles & IDs
Public title
Dietary salt and responses to fluid overload during exercise
Scientific title
High versus low sodium diet and effects on urinary excretion and plasma sodium concentration during exercise with fluid overload in healthy active individuals.
Secondary ID [1] 281085 0
Universal Trial Number (UTN)
Trial acronym
Linked study record

Health condition
Health condition(s) or problem(s) studied:
Exercise associated hyponatraemia 287224 0
Condition category
Condition code
Diet and Nutrition 287549 287549 0 0
Other diet and nutrition disorders

Study type
Description of intervention(s) / exposure
The intervention will consist of 10 days on either a “normal western “, i.e. High salt diet, vs. 10 days on a Low salt diet. Participants will be given a pamphlet in which foods to reduce intake of will be listed and cooking advice will be given prior to commencing the Low salt diet to reduce the dietary salt intake on their own accord. For the High salt diet participants will simply be asked to maintain their normal dietary habits. Participants will fill in a food frequency questionnaire (FFQ) on both diets. The FFQ is being validated at present and the low salt pamphlet developed with New Zealand product examples. On days 7-9 total urinary output will be collected to monitor Na+ output as a measure of intake.
There will be at least 10 days "wash-out" period between two diets. Participants will be able to do their own exercise training (noted in a diary) during the dietary interventions but no exercise on day 9 and on day 10 of each diet they will conduct a 3 hour exercise (cycling or running at 55% VO2max) trial in the heat (34 degrees C) laboratory (supervised by the researchers) in which blood and urine samples will be taken.
Intervention code [1] 285531 0
Comparator / control treatment
High salt diet= normal diet
Control group
Dose comparison

Primary outcome [1] 287796 0
Plasma sodium concentration
Timepoint [1] 287796 0
On day 10 of diet, during 3 hours of (cycle or running) exercise in the heat at 0, 15 minutes and every 30 minutes thereafter.
Primary outcome [2] 287797 0
Urinary excretion (volume and Na+)
Timepoint [2] 287797 0
Day 10
Cumulative urine production during the exercise trial: during the exercise itself, if and when the participant feels the need to urinate, and then immediately following the 3 hour exercise trial.
Secondary outcome [1] 298849 0
Resting blood pressure
This will be measured, in the fasted state, participants having sat for 10 minutes with arm supported, legs uncrossed, with an automated sphygmomanometer. Two measurements will be made and if they are not similar a third measurement will be made. An average of the two (closest) will be taken.
Timepoint [1] 298849 0
Morning day 1 before starting dietary intervention and on day 10 of dietary intervention, prior to exercise trial.

Key inclusion criteria
Endurance trained in running or cycling.
Minimum age
18 Years
Maximum age
45 Years
Can healthy volunteers participate?
Key exclusion criteria
The presence of kidney disease, hypertension and on any medication or supplements other than multivitamins or sports drinks.

Study design
Purpose of the study
Allocation to intervention
Randomised controlled trial
Procedure for enrolling a subject and allocating the treatment (allocation concealment procedures)
Complete cross-over (all subjects do both treatments, with a 10 or more day wash-out in between), randomised order.
The allocation order will be known to researchers and to participants; however, plasma and urine samples will be coded by a separate technician who will not conduct the analyses and thus the results will not be known until the analyses are completed.
Methods used to generate the sequence in which subjects will be randomised (sequence generation)
Random number table for treatment order
Masking / blinding
Blinded (masking used)
Who is / are masked / blinded?

Intervention assignment
Other design features
Not Applicable
Type of endpoint(s)
Statistical methods / analysis

Recruitment status
Date of first participant enrolment
Date of last participant enrolment
Date of last data collection
Sample size
Accrual to date
Recruitment outside Australia
Country [1] 4499 0
New Zealand
State/province [1] 4499 0

Funding & Sponsors
Funding source category [1] 285860 0
Name [1] 285860 0
School of Physical Education , University of Otago PBRF funding
Address [1] 285860 0
PO Box 56 Dunedin 9054
Country [1] 285860 0
New Zealand
Primary sponsor type
School of Physical Education , University of Otago PBRF funding
PO Box 56 Dunedin 9054
New Zealand
Secondary sponsor category [1] 284680 0
Name [1] 284680 0
Address [1] 284680 0
Country [1] 284680 0
Other collaborator category [1] 277033 0
Name [1] 277033 0
Dr Jim Cotter
Address [1] 277033 0
School of Physical Education, Sport & Exercise Sciences, University of Otago PO Box 56 Dunedin 9054
Country [1] 277033 0
New Zealand
Other collaborator category [2] 278712 0
Name [2] 278712 0
Prof Simon Thornton
Address [2] 278712 0
Universite de Lorraine,

Defiance cardiovasculaire, aigue et chronique
Bat. D, 1er etage
Faculte de Medecine
9, Avenue de la foret de Haye,
CS 50184 - 54505 VANDŒUVRE Les Nancy cedex
Country [2] 278712 0

Ethics approval
Ethics application status
Ethics committee name [1] 287885 0
Human Ethics Committee University of Otago, Academic Committees
Ethics committee address [1] 287885 0
Clocktower, PO Box 56, Dunedin 9054
Ethics committee country [1] 287885 0
New Zealand
Date submitted for ethics approval [1] 287885 0
Approval date [1] 287885 0
Ethics approval number [1] 287885 0

Brief summary
The aim is to evaluate the effects of chronic sodium (salt) intake on acute responses to low sodium intake with fluid overload during prolonged exercise
in the heat. It is queried whether a chronic high sodium diet will upregulate sodium excretion, ie less re-absorption in kidney tubules, and result in a greater decrease in plasma sodium with acute fluid overload, during exercise,
than a chronic low sodium diet.
Participants will follow both a High (normal western diet) and Low sodium diet for 10 days (prescribed with detailed dietary instruction) in a randomised order with at least 10 days washout between diets. Urinary outputs (24 hour) will be collected on days 7-9; from these samples urinary sodium will be measured. Participants will fill out food frequency and activity questionnaires.
On day 10, 3 hour exercise sessions (running or cycling) in the heat (55% VO2max, 34 degrees C, 50% rel. humidity). Water will be given every 15 minutes at a rate equalling
the rate of fluid loss in a 1 hour pre-trial of the same exercise in the heat.
Methods will be as used previously by Vrijens & Rehrer (1999) including plasma (0, 15 minutes and every 30 minutes thereafter) and urinary sodium, Hb, Hct, and body mass changes (before and after exercise), sweat sodium and core temperature and heart rate continuously monitored. Exercise will be curtailed if core temp. is above 39.5 degrees C or if plasma sodium drops to <130 mmol/L or voluntary exhaustion.

Vrijens, D. M. V. and Rehrer, N. J. Sodium free fluid ingestion decreases plasma sodium during exercise in the heat. Journal of Applied Physiology 86: 1847 1851 (1999).
Trial website
Trial related presentations / publications
Koenders, E. E., Franken, C. P. G., Cotter, J. D., Thornton, S. N., Rehrer, N. J. Restricting dietary sodium reduces plasma sodium response to exercise in the heat. Scandinavian Journal of Medicine & Science in Sports 2016: doi: 10.1111/sms.12748.
Public notes
Video of the public portion of the conference can be seen at:

Principal investigator
Name 34605 0
A/Prof Nancy J Rehrer
Address 34605 0
School of Physical Education, Sport & Exercise Sciences, Otago University, PO Box 56, Dunedin 9054
Country 34605 0
New Zealand
Phone 34605 0
Fax 34605 0
Email 34605 0
Contact person for public queries
Name 17852 0
A/Prof Dr Nancy J Rehrer
Address 17852 0
School of Physical Education, Otago University, PO Box 56, Dunedin 9054
Country 17852 0
New Zealand
Phone 17852 0
Fax 17852 0
Email 17852 0
Contact person for scientific queries
Name 8780 0
A/Prof Dr Nancy J Rehrer
Address 8780 0
School of Physical Education, Otago University, PO Box 56, Dunedin 9054
Country 8780 0
New Zealand
Phone 8780 0
Fax 8780 0
Email 8780 0

No information has been provided regarding IPD availability
Summary results
Have study results been published in a peer-reviewed journal?
Other publications
Have study results been made publicly available in another format?
Results – basic reporting
Results – plain English summary