How much salt and sodium are we eating - further information
Since we released our May 2009 fact sheet, How much salt and sodium are we eating?,we’ve received lots of questions about the accuracy of our predicted salt intakes and the age of the data we used to generate these intake estimates. This fact sheet is intended to clarify some of these matters.
Salt or sodium - which term means what?
Salt and sodium are not the same thing. The two terms should not be used interchangeably.
Salt is the chemical compound sodium chloride. It is also often called ‘common salt’ or ‘table salt’. Salt has been used in food preparation for thousands of years, not only to provide flavour but to help preserve foods.
Sodium is a commonly occurring element. It is in virtually all foods that we eat, even when they do not have any salt added to them. This is because sodium is naturally present in most foods and is also added to food in other forms. For example, sodium is added to some foods through the use of some food additives, such as sodium ascorbate (a form of vitamin C), 'sodium saccharin (a sweetener)' and sodium metabisulphite (a preservative). When food additives are present in a food, they are identified in the ingredient list, either by name or number.
But the main source of sodium in our diets is sodium chloride, probably providing around 90% of our dietary sodium intake (derived from Jameset al.,1987).
How sodium intake is estimated
The best way to estimate sodium intake is to collect people’s urine over a 24-hour period and measure how much sodium it contains, since this will approximate sodium intake. However, this is not easy to do and is expensive, so has not been used in large scale national surveys in Australia. Measuring urinary sodium excretion does not tell you directly how much salt someone is eating because it measures all sources of sodium, not just sodium from salt. It also doesn’t provide information on which foods contribute most to sodium intake.
Sodium intake can also be estimated by recording how much food and drink a person has over a set period of time (usually one or two days). This information can be matched with data on how much sodium is in different foods, to estimate total sodium intake for that person. Although this approach works well for most nutrients, there are some particular difficulties for sodium because sodium intakes can be increased if salt is added at the table or during cooking. It is hard to accurately estimate how much of this ‘discretionary’ salt is added by each person. Also, different brands of the same food can vary widely in sodium content and this variability may not be captured in nutrient databases.
How salt intake is estimated
Once sodium intakes have been estimated, salt intake can then be calculated from this using the ratio of the molecular mass of sodium chloride (58.44 g/mol) to the atomic mass of sodium (23 g/mol). However it is important to first take into account the proportion of sodium that is not from sodium chloride. If you don’t do this, you will overestimate salt intake. For example, regular milk has a sodium content of 46 mg/100g (FSANZ, 2007) but does not contain any added sodium chloride. Biscuits can have substantial sodium contents (e.g. 290 mg/100g for plain sweet biscuit, see FSANZ, 2007) but a large amount of this will be from sodium bicarbonate or other leavening agents.
How FSANZ estimated Australians’ salt intake
FSANZ was interested in how best to deliver more iodine to Australians – salt with added iodine is an effective tool for increasing a population’s iodine intake. You can read about why we needed to do this at http://www.foodstandards.gov.au/standardsdevelopment/proposals/proposalp230iodinefo2802.cfm . Therefore we needed to estimate how much salt Australians eat each day.
We took food consumption data for 13,858 Australians, aged two years and above, from the 1995 Australian National Nutrition Survey. We matched this food consumption data with data for sodium levels in foods and calculated how much salt this was equivalent to, for every food that was recorded in the 1995 Survey, after adjusting for sodium that comes from non-salt sources. The sodium data we used were largely data from the early 2000s onwards, because we knew there had been some important changes since the time of the Nutrition Survey in the way the Australian food industry uses salt (e.g. see Williams et al, 2003). We then used our custom-built dietary modelling program, DIAMOND, to estimate salt intake for each person in the 1995 National Nutrition Survey. From this, we derived mean and high consumer salt intake estimates. You can read about what we did in more detail at http://www.foodstandards.gov.au/_srcfiles/Salt_Intake_5.pdf .
How do our estimates compare to other Australian research?
Some people have stated that they believe FSANZ’s estimates of salt intake are too low (e.g. see http://www.awash.org.au/documents/AWASH-Statement-on-Australian-Salt-Intakes.pdf ).
Most other Australian research on sodium intakes has estimated total sodium intakes, not salt, although this may sometimes be referred to as salt intake or ‘salt equivalents’. FSANZ’s estimates are for sodium chloride and do not take account of the 10% or more of dietary sodium that comes from other sources. Therefore, it is to be expected that our estimates of sodium from salt will be lower than estimates of total sodium intake.
FSANZ estimated that across all Australians, including young children, mean salt intake is 5.5 grams per day. This amount of salt would deliver an average of 2,150 mg sodium per day. Therefore mean total sodium intakes in Australia, taking into account non-salt sources of sodium, would probably be around 2,500 mg/day. This is equivalent to about 110 mmol sodium per day, which is another way of expressing sodium intake. Because this is an average value, there will be many Australians whose sodium intake is higher than this.
Every technique for estimating nutrient intakes has its limitations. FSANZ acknowledges these limitations in its dietary intake assessment reports. In the case of FSANZ’s work on salt intakes, one of the major limitations is that we had to make assumptions about how much salt people add at the table or during cooking (assumed to be between 0.8 and 1.2 grams per day for those who reported often or usually adding salt). Another limitation is that we used sodium concentration data that are averages of concentrations across food groups (e.g. across all types of white breads), whereas some individuals may regularly eat foods that are higher (or lower) in sodium than the average value.
The 1995 National Nutrition Survey is the most recent national food consumption survey covering Australians from two years of age and above. In most cases it provides the most reliable data available for estimating nutrient intake from the wide range of foods that make up our diets. While consumption of some foods (e.g. sushi) might have changed since 1995, consumption of the main staples of our diet, such as bread and milk, is unlikely to have changed to such an extent that intake estimates would be invalidated.
FSANZ doesn’t believe that it is appropriate to assume salt intake in Australia is the same as that in other developed countries. In particular, the Australian National Heart Foundation, through its Tick program, has been a leader in encouraging reduced salt use in processed foods. Our salt intake estimates are based on Australian food consumption data and data for the composition of Australian foods.
Dietary recommendations about salt and sodium
No national recommendations have been established for salt intake. Instead, national recommendations relate to sodium intake. The National Health and Medical Research Council (NHMRC) (2006) recommend an Upper Safe Level of Intake for sodium of 2,300 mg/day for those aged 14 years and above. The Upper Level of Intake is defined as “the highest average daily intake level likely to pose no adverse health effects to almost all individuals in the general population”. The NHMRC have also set a Suggested Dietary Target of 1,600 mg/day for “ older, overweight hypertensives and for those wishing to maintain low blood pressure over the lifespan”.
Recent research commissioned by FSANZ (Goodall et al, 2008) has shown that reduction in salt levels in processed foods would lead to substantial reductions in cardiovascular disease.
References
Boorman, J., Cunningham, J. Mackerras, D. (2008). Salt intake from processed foods and discretionary salt use in Australia. http://www.foodstandards.gov.au/_srcfiles/Salt_Intake_5.pdf
FSANZ (2007). NUTTAB 2006. Available from http://www.foodstandards.gov.au/monitoringandsurveillance/nuttab2006/index.cfm
FSANZ (2009). How much sodium and salt are we eating? ( http://www.foodstandards.gov.au/newsroom/factsheets/factsheets2009/howmuchsodiumandsalt4340.cfm . Retrieved 15 July 2009
Goodall, S., Gallego, G., Norman, R. (2008). Scenario Modelling of Potential Health Benefits Subsequent to the Introduction of the Proposed Standard for Nutrition, Health and Related Claim. Report developed for Food Standards Australia New Zealand. Centre for Health Economics Research & Evaluation. Available from http://www.foodstandards.gov.au/_srcfiles/P293%20Health%20Claims%20FAR%20Attach%2011_2%20FINAL.pdf
James, WPT, Ralph A, Sanchez-Castillo CP (1987). The dominance of salt in manufactured foods in the sodium intake of affluent societies. Lancet ; i:426-9
NHMRC and Ministry of Health. 2006. Nutrient reference values for Australia and New Zealand. Commonwealth of Australia.
Williams P. McMahon A, Bousted R. (2003) . A case study of sodium reduction in breakfast cereals and the impact of thePick the Tickfood information program in Australia. Health Promotion International; 18:51-6.