4363.0.55.001 - Australian Health Survey: Users' Guide, 2011-13

ARCHIVED ISSUE Released at 11:30 AM (CANBERRA TIME) 15/04/2014

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Contents >> Biomedical Measures >> Sodium biomarker

SODIUM

Definition

Sodium is an essential nutrient required by the body to balance electrolyte levels. Its main function is to maintain water balance in the body. The most common form of sodium in the everyday diet is salt, with 40% composing of sodium and 60% composing of chloride.¹ The level of sodium within the body may vary throughout the day and is dependent on a person’s dietary intake.¹

The sodium test measures the total amount of sodium in the urine that has been excreted from the body at the time of the test. Research has shown that people are consuming far more sodium than is required which can contribute to increased blood pressure and chronic disease such as cardiovascular disease.¹

It should be noted that the most accepted and reliable assessment of sodium excretion is done using a 24 hour urine collection method. However asking participants to collect their urine over 24 hours is burdensome and likely to deter participation. Consequently, only spot urine samples were collected in the National Health Measures Survey (NHMS).

WHO have recommended using a 24 hour urine collection method for establishing a baseline assessment of sodium consumption. However, there are equations and formulas that have been developed to estimate 24 hour sodium excretion from spot urine collections. ^2,3,4,5,6 Note, there are no position statements on the use of these equations and formulas for the Australian population to date, as such estimated 24 hour sodium excretion data has not been reported in the NHMS.

Population

Sodium results were obtained for persons aged 5 years and over, who agreed to participate in the NHMS and provided a urine sample. Fasting was not required for this test.

Methodology

A spot urine sample was collected from participants and urinary sodium levels were measured at the Douglass Hanly Moir (DHM) laboratory.

There is no consensus of epidemiological cut off reference values for measuring sodium excretion from spot or estimated 24 hour urine collections, as such no cut off points have been defined in the NHMS.

Further information about the analysis method and machines used to measure sodium levels are available in Excel spreadsheet format in the Downloads page of this product.

Data items

The data items and related output categories for this topic are available in Excel spreadsheet format from the Downloads page of this product.

Interpretation

Points to be considered when interpreting data for this topic include the following:

The urinary excretion of sodium varies significantly with dietary intake and there is no method to determine expected values based on a spot urine collection. It should be noted that other studies and research may have collected and measured 24 hour urine sodium excretion. The data from this topic should therefore be used with caution when comparing spot sodium excretion data with measured or estimated 24 hour urine sodium excretion data.
There are a number of different test methods to measure sodium levels and each test method may produce different results. The data from this topic should therefore be used with caution when comparing sodium results from other studies using a different test method.

Comparability with other surveys

The NHMS is the first ABS survey to collect biomedical data on sodium levels.

Sodium data has been collected in other non-ABS surveys. However, caution must be taken when interpreting results due to the differences in scope, assay and instrument, and any thresholds applied in the final analysis.

ENDNOTES

1 Gibson RS, 2005, Principles of Nutritional Assessment, 2nd ed, New York: Oxford University Press.
2 Brown IJ, Dyer AR, Chan Q, Cogswell ME, Ueshima H, Stamler J, & Elliott P, 2013, ' INTERSALT Co-Operative Research Group, 2012, 'Estimating 24-Hour Urinary Sodium Excretion From Casual Urinary Sodium Concentrations in Western Populations', American Journal of Epidemiology, 1;177(11):1180-92.
3 Pan American Health Organization/ World Health Organization, 2010, 'Protocol for population level sodium determination in 24‐hour urine samples' ,WHO/PAHO Regional Expert Group for Cardiovascular Disease Prevention through Population]wide Dietary Salt Reduction, <http://new.paho.org/hq/dmdocuments/2010/pahosaltprotocol.pdf>, Last accessed 14/04/2014.
4 Kawasaki T, Itoh K, Uezono K & Sasaki H, 1993, 'A simple method for estimating 24 h urinary sodium and potassium excretion from second morning voiding urine specimen in adults', Clinical and Experimental Pharmacology and Physiology, 20(1):7–14.
5 Tanaka T, Okamura T, Miura K, Kadowaki T, Ueshima H, Nakagawa H, & Hashimoto T, 2002, 'A simple method to estimate populational 24-h urinary sodium and potassium excretion using a casual urine specimen', Journal of Human Hypertension, 16(2):97-103 <http://www.nature.com/jhh/journal/v16/n2/full/1001307a.html>, Last accessed 14/04/2014.
6 World Health Organization 2011, Strategies to monitor and evaluate population sodium consumption and sources of sodium in the diet: report of a joint technical meeting convened by WHO and the Government of Canada, Report, 3-40. Geneva, Switzerland, WHO Press, <http://whqlibdoc.who.int/publications/2011/9789241501699_eng.pdf>, Last accessed 8/04/2014.