Last partial update: February 2018 - Please read disclaimer before proceeding.

 

What are salt and sodium and how much do we need and consume?

Excess sodium in the diet increases the risk of developing high blood pressure. There are numerous sources of dietary sodium, the most common one being normal table salt (i.e. sodium chloride). Other common sources include MSG (monosodium glutamate), baking powder (sodium bicarbonate), sodium salts used in emulsifiers, and preservatives, such as sodium metabisulphite. This section will therefore mainly refer to sodium rather than salt.

To maintain normal body function, people only need an intake of 8.5mmol/day (200mg/day) of sodium. To prevent hypertension, the National Health and Medical Research Council recommends a maximum daily intake of sodium for adults of 40 to 100 mmol/day (or 920 to 2300 mg/day). Adverse effects on the body start to occur at an intake of about 50mmol/day. In Australia, only about six per cent of males and 36 per cent of females have sodium intakes less than 100mmol/day 2300mg/day), with the average Australian diet in 2018 containing about 300 mmol/day (or 6900mg / day) of sodium for women and about 350 to 400 mmol/day (or 8050 to 9200mg / day) of sodium for men.

Roughly 90 per cent of the sodium consumed in the diet is excreted in urine. Thus, if required, a doctor can easily determine a person’s daily sodium intake by collecting their urine for 24 hours and measuring the sodium content.

Reducing sodium intake has been shown to significantly reduce both systolic blood prrssure (the upper reading) and diastolic blood pressure (the lower reading) in people with high blood pressure. Not surprisingly, this effect is much less in people with normal blood pressure. (They are probably consuming less sodium in the first place.) 

Reducing dietary sodium

A major problem associated with reducing sodium intake is that in the average Australian’s diet, only 20 per cent of the sodium consumed is added by the consumer. The other 80 per cent is already added to bought foods (70 per cent) or is naturally occurring in food (10 per cent).

The main foods that contribute to sodium in the diet are bread, spreads such as butter and margarine, cheese, biscuits, takeaway foods, and sauces. (A list of the foods that people need to monitor if they are to reduce their sodium intake can be found in the boxed section below.) The contribution of each food to sodium intake depends on the amount of the food the person eats as well as the sodium content of the food. For example, the vegemite in a vegemite sandwich has a much higher sodium concentration than the bread, but the bread provides more sodium because there is much more of it.

 

Some foods with large amounts of sodium

Very high sodium content  (over 1000 mg of salt in 100 grams of food)
Anchovies, meat tenderisers, MSG, soy sauce (even the low salt variety), gravy powder, normal salt, stock cubes, meat extract, ham, salami, corned beef, meat pies, bacon, sausages, spring rolls, dim sims, smoked salmon, salted pretzels, parmesan cheese, blue-vein cheese, cheese spread, processed cheddar cheese, olives, kelp, normal baking powder, crumpet, flavoured cracker biscuits.

High sodium content (400 to 1000 mg of salt in 100 grams of food )
Bread, luncheon meat, pate, potato crisps, frankfurts, pizza, hamburger, fried takeaway foods, canned / packet soups, canned fish (salmon, tuna), butter, hard cheeses, pies, sausage rolls, Chinese and Lebanese foods, savoury biscuits, some cereals (Corn Flakes, Rice Bubbles, Special K, Coco Pops, Frosties, Nutri-grain, Fruit Loops, Weeties, Lite Start), some soda waters, most sauces (excluding mayonnaise, coleslaw dressing, Italian dressing)

Medium sodium content (120 to 400 mg of salt in 100 grams of food)
Sweet biscuits, salted nuts, canned vegetables, toasted muesli, cheesecake, cottage cheese and ricotta, mozzarella cheese, hot chips, caramels, toffee, pastry, cakes.

Many of the above products do come in salt-reduced / low salt varieties. This should be evident from the product information on the label.

 

Some foods taste ‘salty’, making their high sodium content obvious. However, many foods are able to hide their added sodium quite well so that it is difficult to taste. The sugar in sweet processed foods hides the taste of sodium very well; for example in cakes, biscuits and some breakfast cereals. The sodium added to cakes and biscuits comes mainly from the baking powder used in their preparation.

Bread is a very important source of sodium and contributes about 25 per cent of daily sodium intake. There are some ‘salt-reduced’ breads and it is important to purchase these types of bread if serious about reducing dietary sodium intake. People can also make their own ‘no added salt’ bread at home. The sodium content of ‘normal breads’ does vary, so if a ‘low-salt’ variety is not available, look at the product information on the packaging to find out which has the least sodium. Similarly, breakfast cereals vary widely in their sodium content, so try to choose one with a low level.

With regard to the rest of the diet, the best way to reduce sodium intake is to reduce the quantity of prepared foods purchased. Try to prepare as many meals as possible at home from fresh ingredients or ingredients that are labelled ‘salt reduced’ or have ‘no salt added’.

Many brands of packaged products used in home cooking, such as tomatoes and stocks, have no salt added. There are even unsalted peanut butters. Look for these rather than the ones with added salt. They will normally have ‘no added salt’ displayed on the label. People can also tell by looking at sodium content data displayed in the ‘nutritional information’ label.

If the family is used to having salt added to their food, ask them to be patient. Although their food will initially taste different, they will usually get used to the difference in about two to three weeks and eventually they will prefer their food without salt. The impact of reducing salt in meals can be lessened by adding flavour substitutes, such as herbs, curry spices, garlic, onion, lemon, lime, vinegar, plum jam etc.

Blood pressure reduction with sodium restriction takes several months

When trying to reduce blood pressure by reducing salt intake, please remember that it takes about three months for any effect on blood pressure to occur. A low salt diet in a person with normal blood pressure will not reduce their blood pressure significantly.

 

Labelling and ‘salt reduced’ foods

There are now low salt alternatives for many foods traditionally high in sodium, such as sauces and spreads. There are several different label wordings that indicate a reduced salt level. These labels are as follows.

A ‘Low salt’ label, which indicates that the product contains less than 120 mg of salt per 100 grams of food. (This is equal to 0.3 per cent salt content.)

A ‘Salt free or unsalted’ label, which indicates that the product contains no added salt and has been made from products that have not had any salt added.

A ‘Salt reduced’ label, which indicates that the product contains at least 25 per cent less salt than its regular counterparts.

 

Who should be careful about going on a low salt diet?

People should consult their doctor before commencing a low-sodium diet if they have a kidney or gastrointestinal disease that causes them to lose sodium or if they are on any of the following medications: blood pressure medication, fluid tablets (diuretics) or lithium.

Women who are pregnant should keep to their usual sodium intake.

People should not use potassium chloride based ‘salt substitutes’ if they have kidney disease or with certain fluid tablets (ask a doctor).

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Prevention of hypertension

As hypertension is a very common disease in adult Australians, everyone needs to consider adopting the measures mentioned below to prevent this disease. These measures are especially important for those with an increased risk of developing hypertension, including the following.

 

Ways of helping reduce / prevent hypertension
A variety of lifestyle changes can help reduce / prevent hypertension, including the following. (Reducing sodium in the diet is dealt with in detail below. The other measures are covered in other sections of this web site.)

Adopting the above measures can;

Effect of reversing poor lifestyle choices on blood pressure

Lifestyle problem and optimum target

Estimated reduction in systolic (upper) BP level

Inadequate physical activity*
(moderate intensity 3 to 4 times a week)

4 mmHg*

Excessive weight
(BMI < 25)

2 mmHg for each kg of weight lost

Excessive sodium consumption
(to 100mmol per day or less)

5 to 7 mmHg
( This effect takes several months to occur.)

Excessive alcohol consumption*
(Less than 4 standard drinks per day for men and 2 for women.)

3 to 4 mmHg*

Excessive saturated fat consumption*
(To less than 10% of total energy intake)

2 to 3 mmHg*

* Successfully overcoming this lifestyle factor has an additional benefit through increasing weight loss.

 

Target levels - How far should BP be lowered?

 

Generally speaking, any lowering of BP towards a level of 115/80 is beneficial with respect to reducing cardiovascular risk. However, only those at the greatest risk of cardiovascular disease need to achieve such low levels. The target levels for different groups are shown in the table below.

It is important to be aware that there can occasionally be problems in lowering BP too much. In some people, especially the elderly, a BP of 140/90 may be too low and cause problems such as dizziness that can lead to injuries from falls. In these circumstances, a doctor may quite appropriately aim to maintain BP at a higher level.

Blood pressure normally peaks in the early morning at about 4am to 6am and thus if medication is taken once daily in the morning it will miss this peak. Thus, consideration should be given to taking once daily medication at night. Taking medication before bed also has the benefit of minimizing the effect of side effects such as dizziness and fatigue.

Blood pressure treatment targets

Group

Target BP

Adults over 65 yrs unless in a category below

Less than 140/90

Adults under 65 yrs
Adults with diabetes
Adults with pre-existing vascular disease
Adults with renal impairment
Adults with 0.25g to 1.0g of protein in their urine per day

Less than 130/85

Adults with over 1.0g of protein in their urine per day

Less than 125/75

 

Further information  

Salt Matters (a web site and publication regarding salt)
Beard TC. Salt Matters: A consumer guide. Lothian Books, Melbourne; 2004
www.saltmatters.org

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