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Trial registered on ANZCTR

Registration number

ACTRN12616000239460

Ethics application status

Approved

Date submitted

15/02/2016

Date registered

22/02/2016

Date last updated

24/01/2017

Type of registration

Prospectively registered

Titles & IDs

Public title

Can increased sodium intake reduce the risk of exercise associated hyponatraemia ?

Scientific title

Can increased sodium intake reduce the risk of exercise associated hyponatraemia in healthy male athletes?

Secondary ID [1]

none

Universal Trial Number (UTN)

Trial acronym

Linked study record

Health condition

Health condition(s) or problem(s) studied:

exrcise associated hyponatraemia

Condition category

Condition code

Diet and Nutrition

Other diet and nutrition disorders

Metabolic and Endocrine

Other metabolic disorders

Intervention/exposure

Study type

Interventional

Description of intervention(s) / exposure

We will utilise a randomised cross-over intervention in which participants will perform two, 3 h exercise trials (cycle ergometry @ workload to elicit 55% VO2max, determined in a graded maximal exercise test on a separate day) in the heat (34 degrees C, controlled climate chamber), periodically ingesting a beverage, with either 60 or 20 mmol Na+/L and the rate of plasma sodium change monitored. The experimental protocol is based upon earlier work (Vrijens & Rehrer, 1999). The beverages will use a base of Gatorade (5.94% glucose 20 mmol Na+/L ) to which NaCl will be added to bring to 60 mmol Na+/L for intervention beverage. (a pre-trial will be done for acceptability and if unpalatable or gastrointestinal distress a mix of NaCl and sodium citrate will be used). The volume given will be determined by net body mass losses in a 1 h exercise pre-trial conducted on a separate day prior to experimental trials under the same conditions (specified amount of water given). The amount of fluid provided in 3 h experimental trials will be at a rate (given every 15 min) to replace mass loss observed in the 1 h trial (i.e. slight excess since some mass loss is due to substrate metabolism). This will be measured out in advance, chilled and provided to participants who will be told to ingest completely as quickly as possible. No other beverage will be ingested. A researcher will be continually supervising participants during exercise trials. During trials heart rate and rectal temperature will be continually monitored. If age predicted heart rate maximum or a core temperature of 39.5 degrees C is reached exercise will be stopped. Experimental trials will be separated by at least 7 days. The evening before trial 1 litre of sports drink (Gatorade [5.94% glucose 20 mmol Na+/L] provided) will be ingested. Breakfast is to be consumed 2 h before the first experimental trial, which will be of their choice, but they will be required to eat this same meal before the second trial. They will also be instructed to drink 1 L of a sports drink (provided) the evening before each trial. On the day of the trial before coming to the laboratory, they may drink water ad libitum, but may ingest no other foods or fluids after breakfast. In addition, the subjects will be instructed to refrain from strenuous exercise 24 h before each trial.

Intervention code [1]

Prevention

Comparator / control treatment

Same exercise and volume of fluid ingestion but with 20 mmol/L sodium in beverage, which is similar to most sports drinks.

Control group

Dose comparison

Outcomes

Primary outcome [1]

Change in plasma sodium concentration

Timepoint [1]

Baseline prior to exercise and every 30 min thereafter until exercise ceases.

Secondary outcome [1]

Change in core temperature, with a rectal thermistor and Squirrel data logger.

Timepoint [1]

Measures continually and means per 15 min time period will be calculated across 3 h of exercise or until exhaustion.

Secondary outcome [2]

Change in heart rate, with a Polar heart rate monitor which consists of a chest strap and wrist band.

Timepoint [2]

Measures continually and means per 15 min time period will be calculated across 3 h of exercise or until exhaustion.

Secondary outcome [3]

Ratings of perceived exertion

Timepoint [3]

Assessed very 15 min across 3 h of exercise or until exhaustion

Secondary outcome [4]

Exercise time (exhaustion) assessed by review of recorded time participant stopped exercising.

Timepoint [4]

During 3 h of intended exercise

Secondary outcome [5]

Plasma volume change as determined by haemoglobin and haematocrit (Dill & Costill, 1974)

Timepoint [5]

At rest, after sitting for 10 min, and every 30 min during exercise for 3 h or until exhaustion.

Secondary outcome [6]

Urine sodium output, by volume produced and [Na+] (Flame photomtery).

Timepoint [6]

Collected as produced during exercise and immediately following exercise.

Secondary outcome [7]

Sweat sodium excretion.
Determined by volume produced (estimated by body mass change corrected for fluid in and urinary output) and sweat [Na+] determined by flame photometry.
Sweat from 4 patches attached on thigh, back, chest and arm..

Timepoint [7]

Sweat patches attached at the beginning of exercise and removed after 1 h of exercise.
Body mass measured at the before and at end of exercise.

Eligibility

Key inclusion criteria

Endurance trained males. This does not need to be cycle specific.

Minimum age

18 Years

Maximum age

55 Years

Sex

Males

Can healthy volunteers participate?

Yes

Key exclusion criteria

Smokers
On prescription medications (except nutritional supplements) or other drug use (except caffeine),
Have kidney disease or diabetes,
Contraindications to participate in maximal exercise.

Study design

Purpose of the study

Prevention

Allocation to intervention

Randomised controlled trial

Procedure for enrolling a subject and allocating the treatment (allocation concealment procedures)

Beverage prepared by just one staff member sodium content unknown to others, labelled by code.

Methods used to generate the sequence in which subjects will be randomised (sequence generation)

Random number generator

Masking / blinding

Blinded (masking used)

Who is / are masked / blinded?

The people receiving the treatment/s

The people assessing the outcomes

Intervention assignment

Crossover

Other design features

Phase

Not Applicable

Type of endpoint/s

Safety/efficacy

Statistical methods / analysis

Based upon earlier work (Vrijens & Rehrer, 1999) and the rate of plasma sodium change observed, with a similar protocol with ingestion of water versus a typical sports drink with 18 mmol/L sodium, we calculated a sample size of 12 to detect a difference of 1.6 mmol/L/h, with standard deviation of 1.5 mmol/L/h, a=.05, power= .90, for paired samples. A target sample size of 14 will be recruited to allow for drop outs or experiments in which technical error occurs.
Data will be analysed by linear mixed effects model analysis of variance, with time as a fixed effect and subject as a random effect, for data collected over time.

Recruitment

Recruitment status

Active, not recruiting

Date of first participant enrolment

Anticipated

1/03/2016

Actual

5/04/2016

Date of last participant enrolment

Anticipated

30/04/2016

Actual

9/01/2017

Date of last data collection

Anticipated

2/02/2017

Actual

Sample size

Target

Accrual to date

Final

Recruitment outside Australia

Country [1]

New Zealand

State/province [1]

Otago

Funding & Sponsors

Funding source category [1]

University

Name [1]

School of Physical Education Sport & Exercise Sciences, University of Otago

Address [1]

PO Box 56
Dunedin 9054

Country [1]

New Zealand

Primary sponsor type

University

Name

School of Physical Education Sport & Exercise Sciences, University of Otago

Address

PO Box 56, 46 Union ST West
Dunedin 9054 ,
New Zealand

Country

New Zealand

Secondary sponsor category [1]

None

Name [1]

Address [1]

Country [1]

Ethics approval

Ethics application status

Approved

Ethics committee name [1]

University of Otago HUman Health Ethical Committee

Ethics committee address [1]

c/o Gary Witte, Manager Committees
Registry
PO Box 56
University of Otago
Dunedin 9054

Ethics committee country [1]

New Zealand

Date submitted for ethics approval [1]

18/12/2015

Approval date [1]

15/02/2016

Ethics approval number [1]

H16/002

Summary

Brief summary

Exercise associated hyponatraemia is a life threatening condition that can occur in (ultra-) endurance athletes who exercise for long periods of time. The primary risk factor is overhydration with hypotonic fluid, i.e. drinking at a greater rate than any excess can be excreted (Hew-Butler et al 2015). However, other factors can play a role, including sodium losses (Godek, et al 2008) and intakes (Vrijens & Rehrer, 1999). Although ingesting a beverage with 18 mmol/L sodium reduces the rate of decline in plasma sodium when compared with water (during endurance exercise in the heat) it still does decline. Sweat sodium ranges from ~30-80 mmol/L and studies with 60 mmol/L sodium (oral rehydration solutions) in clinical situations (at rest), in which plasma sodium is compromised via losses, result in improved hydration and normalisation of plasma sodium. Therefore, we intend to test the efficacy of a beverage with 60 mmol/L sodium, when consumed in slight excess (i.e. approximately matching body mass loss) throughout longlasting exercise in the heat (34 degrees C) in healthy, endurance trained individuals. The purpose of this study is to establish whether increasing the concentration of sodium in a beverage (~ 3 times that normally in sports drinks), can keep blood sodium concentration from decreasing during longlasting exercise in the heat, when fluid is ingested in amounts to nearly match body weight loss.
The hypothesis is that ingesting a beverage with 60 mmol/L of sodium during 3 h of cycling in the heat will prevent the fall in blood sodium that typically occurs with a beverage with 18-20 mmol/L of sodium. We will utilise a randomised cross-over intervention in which participants will perform exercise in the heat, and will ingest a beverage with one of two concentrations of sodium (20, 60 mmol/L) and then repeat the trial with the alternate concentration.

Trial website

Trial related presentations / publications

Public notes

Contacts

Principal investigator

Name

A/Prof Nancy J Rehrer

Address

School of Physical Education Sport & Exercise Sciences
University of Otago
PO Box 56, 46 Union St West
Dunedin 9054

Country

New Zealand

Phone

+6434799128

Fax

[email protected]

Contact person for public queries

Name

A/Prof Nancy J Rehrer

Address

School of Physical Education Sport & Exercise Sciences
University of Otago
PO Box 56, 46 Union St West
Dunedin 9054

Country

New Zealand

Phone

+6434799128

Fax

[email protected]

Contact person for scientific queries

Name

A/Prof Nancy J Rehrer

Address

School of Physical Education Sport & Exercise Sciences
University of Otago
PO Box 56, 46 Union St West
Dunedin 9054

Country

New Zealand

Phone

+6434799128

Fax

[email protected]

No information has been provided regarding IPD availability

What supporting documents are/will be available?

No Supporting Document Provided

Results publications and other study-related documents

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Update to Study Results

Doc. No.	Type	Is Peer Reviewed?	DOI	Citations or Other Details	Attachment
4588	Conference abstract	No		Rehrer NJ, Wijering L, Cotter JD. Can Increased So... [More Details]	370124-(Uploaded-27-12-2018-05-54-01)-Other results publication.pdf

Documents added automatically

Source	Title	Year of Publication	DOI
Dimensions AI	A randomized, cross-over trial assessing effects of beverage sodium concentration on plasma sodium concentration and plasma volume during prolonged exercise in the heat	2022	https://doi.org/10.1007/s00421-022-05025-y

N.B. These documents automatically identified may not have been verified by the study sponsor.

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