Position statement - Salt and cancer risk

Key messages

Salt is a compound of the elements sodium and chlorine, and is commonly used to flavour and preserve foods. Most of the salt we eat comes from processed and packaged foods such as sauces, processed meats, stock cubes and soups as well as breads and cereals. Evidence suggests that there is a probable causal relationship between both salt and salt preserved foods and stomach cancer risk. Salt is also a leading cause of high blood pressure and cardiovascular disease. Cancer Council Australia supports the recommendation made by the National Health and Medical Research Council’s (NHMRC) Australian Dietary Guidelines that people choose diets that limit salt intake through avoiding adding salt in cooking or at the table, and through choosing fresh unprocessed foods over processed foods. Cancer Council Australia supports efforts to reduce population salt intakes, particularly through reducing salt levels in processed and takeaway foods. For general health and wellbeing, people should aim to consume no more than 2300 mg of sodium (6 g of salt) per day. Ways to limit salt intake include purchasing “no added salt” or “low salt” foods in the supermarket, flavouring foods with herbs and spices instead of salt, eating more fresh fruit and vegetables and limiting processed and take-away foods.

Background

Salt contains both sodium and chlorine, and is chemically known as “sodium chloride”. Salt is commonly used to flavour and preserve foods. Before refrigeration was common, large amounts of salt were needed to prevent foods from spoiling. In recent times the need for salt in foods has decreased.

Salt is the main source of sodium in the diet, which is essential for the body to function normally. However, the requirement for sodium in the body is much less than the amount usually eaten. Most of the salt eaten comes from processed and packaged foods such as sauces, processed meats, stock cubes and soups as well as breads and cereals (see Table 1 and Table 2).

Salt in our diet also comes from the salt added at the table and in cooking. Table salts often include additives like anti-caking agents to stop the salt crystals from sticking together. Salt can also be flavoured with things like celery or garlic.

High amounts of salt in the diet have been linked with stomach cancer. Salt is also a leading cause of high blood pressure and increases the risk of cardiovascular disease.

Table 1. Sodium (Na) content per 100 g of different foods

Food	Na (mg)	Food	Na (mg)	Food	Na (mg)
Bread, white	451	Turkey, deli style	820	Salami, Danish	1495
Gravy	468	Devon	844	Spam	1539
Meat pie	500	Beef sausages	910	Leg ham	1650
Sponge cake	610	Chicken noodle soup	922	Pretzels	1980
Butter	610	Tomato sauce	938	Bacon, fried	2000
Pad Thai noodles	610	Biscuit, cheese	955	Vegemite	3000
Hamburger, plain	614	Dim sim, fried	1091	Oyster Sauce	3790
Cheese, cheddar	662	Cheese, feta	1107	Anchovy	5480
Chiko roll	694	Corned beef	1190	Soy sauce	6555
Mayonnaise	700	Cream cheese	1249	Fish sauce	7990
Margarine	780	Smoked salmon	1266	Taco seasoning	9350
Cornflakes	815	Italian dressing	1330	Stock cube	18400
Scone, plain	820	Olive, green or black	1472	Table salt	38178

Table 2. Main sources of salt in processed foods

Food category	% contribution to salt intake from processed foods
Cereal and cereal products	32
Cereal-based products and dishes	17
Meat, poultry and game products and dishes	21
Milk products and dishes	5
Savoury sauces and condiments	8
All other foods	17

Epidemiological evidence

The World Cancer Research Fund (WCRF) found that there is probable evidence that both salt and salt preserved foods are associated with an increased risk of stomach cancer. Probably is the second highest level of evidence of a link and denotes a causal association. This finding is consistent with other review articles, and the World Health Organization report published in 2003, which classified salt preserved foods and salt as probably causing stomach cancer.

Although it is difficult to measure salt intake, the effect of salt on stomach cancer is thought to be mainly due to a regular intake of salted and salt preserved foods rather than salt per se. This is partly because these foods are eaten widely in Japan and other Asian countries, where the incidence of stomach cancer is high. In addition, countries with traditional diets that include substantial amounts of salty (rather than salt preserved foods) also have high rates of stomach cancer.

In 2009, WCRF estimated that 16% of stomach cancer in the US, and 14% in the UK was attributable to high salt intake. WCRF recommends that people avoid salt preserved, salted or salty foods, and that foods be preserved using methods that don’t involve salt (e.g. refrigeration, freezing, drying, bottling, canning or fermentation).

Stomach cancer

There has been a decline in stomach cancer rates in Australia since the 1970s. Stomach cancer was ranked twelfth for incidence and ninth for mortality in Australia in 2007. Australian males are twice as likely to be diagnosed with stomach cancer and to die from it. The observed incidence of stomach cancer is higher in migrants to NSW, particularly in those from China.

A meta-analysis of seven case-control and four cohort studies found an association between high salt intake and stomach cancer risk (odd ratio (OR)= 2.05, 95% confidence interval (CI)= 1.60-2.62).

Another meta-analysis of seven prospective studies investigating a link between high salt intake and stomach cancer risk found that dietary salt intake was directly associated with risk of stomach cancer in a dose-responsive manner. "High" salt intake (relative risk (RR)= 1.68, 95% CI= 1.17-2.41) and "moderately high" salt intake were both associated with increased risk of stomach cancer (RR= 1.41, 95% CI=1.03-1.93).

Potential mechanisms of action

Experimental studies suggest that salt may be linked to stomach cancer because a high intake of salt may directly damage the stomach lining or increase endogenous N-nitroso compound formation.

There is also some research which suggests that salt intake may cause stomach cancer only in those who have both Helicobacter pylori infection and have been exposed to a chemical carcinogen.

A lack of iodine in the diet can cause hypothyroidism, and there is some concern it may increase the risk of thyroid cancer. Cancer Council Australia needs to maintain a watching brief on the Food Standards Australia and New Zealand debate on iodine fortification in the food supply. It may be that the daily allowance of salt is best met with the use of iodised salt to reduce the risk of thyroid cancer. However, reasons for iodine fortification centre mainly on the need to prevent cretinism and goitre.

Current consumption levels in Australia

The 2011–2012 National Nutrition and Physical Activity Survey found that the average daily amount of sodium consumed from food for all persons aged two years and over was 2,404 mg per day (equivalent to around one teaspoon of table salt). This amount includes sodium naturally present in foods and salt added during processing, but excludes the 'discretionary salt' added by consumers in home prepared foods or 'at the table'. Given the survey estimates 64% of people add discretionary salt, these numbers are likely to be an underestimate.

Sodium consumption is significantly higher among males than females, and peaks among males aged 14–30.

The 2007 Survey of Australian Consumer Awareness and Practices Relating to Salt found the following among Australian adults:

• Nearly three-quarters of survey participants were concerned about salt in their diet.
• More than half thought that they were probably eating either less than or about the amount of salt recommended by the National Heart Foundation. However only a small minority actually knew the recommended maximum daily intake.
• Almost three-quarters of people correctly identified the main source of salt in the Australian diet as processed foods. Knowledge of the salt content of other foods (e.g. white bread and breakfast cereals) was not good.
• One-third reported that they regularly tried to buy ‘low salt’ or ‘no added salt’ foods. A fifth reported regularly acting on the information they found about salt on food labels.
• One-fifth reported that they often added salt during cooking and one-fifth reported often adding salt at the table.

Recommendations

Cancer Council Australia: Supports the recommendation made by the NHMRC Australian Dietary Guidelines that people choose diets low in salt; Recommends that people avoid adding salt at the table or in cooking; and Supports the Food and Health Dialogue established by the Federal Government to engage the food and catering industries to reduce salt in processed foods. The nutrient reference values for Australia and New Zealand recommend an upper limit of 2300 mg of sodium a day for adults, with an adequate intake of 460-920 mg per day of sodium. To reduce the current level of cardiovascular disease, the National Heart Foundation recommends that all Australians reduce their salt intake to less than 6 g of salt per day (about 2300 mg sodium), which is approximately 1½ teaspoons of salt. People with hypertension or those with or at risk of cardiovascular disease should reduce their salt intake to less than 4 g a day. For general health and well-being, people should aim to consume no more than 2300 mg of sodium (6 g of salt) per day.

Reducing salt intake

People can limit their salt intake by purchasing “no added salt” or “low salt” foods in the supermarket. A “low salt” food contains less than 120 mg of sodium per 100 g. “Reduced salt” products can be purchased too if these are the lowest salt options available.

Products with the Heart Foundation Tick can be good options for consumers as they meet strict standards set by the National Heart Foundation for the amount of sodium/salt they contain.

Other ways people can lower the amount of salt they eat include:

• Consuming more fresh fruit and vegetables;
• Flavouring foods with herbs and spices instead of salt;
• Limiting take-away foods;
• Reducing intake of dehydrated foods such as seasoning mixes and soups;
• Cutting back on the amount of pre-packaged sauces and condiments used;
• Swapping salty snacks like pretzels, salted nuts and potato chips for fruit, low fat yoghurt or low-salt crackers;
• Limiting consumption of processed meats, such as sausages and salami;
• Choosing fish canned in spring water rather than fish canned in brine; and
• Buying bread that hasn’t had salt added to it, or make bread at home in a bread machine.

It is important to keep in mind that some foods (such as wholegrain bread) do have salt in them, but still contribute important nutrients to the diet and may help to lower the risk of certain cancers.

As the evidence for salt and cancer risk is mainly related to stomach cancer, and the incidence of this cancer in Australia is not particularly high, reducing salt intake by limiting foods such as processed foods and take-away items confers the highest overall benefit. In this way, nutritional intake is not compromised and the energy density of the diet is lowered, helping to maintain a healthy body weight (which is associated with a lower risk of certain cancers).

Future research

In the future, there is a need for more studies that:

• Investigate further the mechanisms behind salt intake and stomach cancer risk; and
• Determine the effect of low sodium salts/salt substitutes (such as those that contain potassium chloride) on cancer risk.

Position statement details

This position statement was reviewed and approved by the Public Health Committee August 2008, and updated October 2013.

Acknowledgements

This position statement was reviewed by:

• Ian Olver
• Jacqui Webster
• Bruce Neal
• Helen Dixon
• Craig Sinclair
• Monica Robotin
• Dorothy Reading