Salt is added to food to enhance its flavour, act as a stabiliser, retain moisture and to help products last longer on the shelf. As a preservative, it prevents foods such as fish and meats from spoiling as most bacteria and moulds cannot grow in very salty environments. In fact, salt was so highly valued in fridge-free, Ancient Rome, that soldiers received a salt allowance as part of their pay. They were literally ‘worth their salt’.
Why you need some salt
Common salt dissolves in body fluids to form sodium and chloride ions. When sodium enters your cells, it is forced out again by millions of tiny salt pumps which exchange the sodium for potassium ions. This creates a small, negative, electric charge across each of your cell membranes which is vital for life. Without sodium, your nerve and brain cells would not pass messages to one another, and your heart muscle cells could not contract. A certain amount of salt is therefore essential for health. So much so, that the transport of salt in and out of our cells is one of the main energy-consuming processes in your body. Physiologists estimate that keeping these sodium-potassium pumps working accounts for a third of the calories you eat.
How much salt do you need?
Humans evolved on a diet providing less than 1g of salt a day. An average adult weighing 70kg can maintain a healthy sodium balance with an intake of as little as 1.25g salt per day – as long as they don’t lose excessive amounts by sweating heavily.
Populations with intakes of less than 3g salt per day do not develop increasing blood pressure with age, and the Yanomami Indians of Brazil, who have a typical salt intake of less than 1g a day, have an average blood pressure of just 96/60mmHg. They don’t develop hypertension – unless they start to follow a western diet.
Ideally, you should eat less than 3g salt per day, too, but as it is added to so many processed foods this would be difficult to achieve. Guidelines therefore recommend that everyone from the age of 11 onwards should obtain no more than 6g salt per day from their diet – around one level teaspoon. Target maximum intakes for children are proportionately smaller as follows:
Traditionally, the majority of salt came from adding it during cooking and at the table. Now these sources are minimal compared to the amounts consumed in processed foods such as canned products, ready-prepared meals, biscuits, cakes and breakfast cereals. Some foods (eg salted bacon, some cereals and ready meals) are at least as salty as seawater which contains between 2.5g and 3.5g of salt per 100g water.
A typical microwave meal contains around 5g salt, a bowl of breakfast cereal adds 1g, and a serving of canned soup adds another 2g.
As a result of these hidden intakes, the average adult eats around 9g salt a day, and some get 12g of salt a day – twice the recommended level of 6g per day – or more.
Why excess salt is bad for your blood pressure
A significant number of people inherit genes that mean their kidneys are unable to excrete excess sodium – especially if their potassium intakes are low. Excess salt causes fluid retention, stiffening of artery walls and increases the thickness of the left ventricle of the heart. These effects all promote a raised blood pressure which, in turn, increases your risk of developing kidney failure, a heart attack or stroke.
In an important study, known as the Dietary Approaches to Stop Hypertension (DASH) Sodium trial, volunteers ate either the DASH diet (high in fruits, vegetables and low-fat dairy) which is known to lower blood pressure, or a typical western diet which is associated with a raised blood pressure. Within each of these groups, some were also asked to follow a high sodium diet (8g/day), some a moderate sodium diet (6g/day) and some a low sodium diet (4g/day) for 30 days.
Whether volunteers followed the DASH diet or the typical western diet, their blood pressure was lowest if their sodium intake was low. Blood pressure reductions were greatest for those with hypertension, with blood pressures falling, on average, by 8.3/4.4 mmHg on the low sodium diet. Even people with a normal blood pressure saw benefits, with their BP falling, on average, by 5.6/2.8 mmHg. As expected, the combination of the DASH diet plus salt restriction had the best blood pressure lowering effect.
The benefits of cutting back on salt
Results from 34 trials assessed the effects of a realistic sodium reductions equivalent to reducing salt intake by 4.4g per day. This showed that blood pressure fell significantly, within four weeks of reducing salt intakes, by an average of 5.39/2.82 mmHg in people with hypertension, and by 2.42/1.0 mmHg in those with a normal blood pressure.
Researchers have predicted that if people with hypertension cut back to an optimal amount of no more than 6g salt per day, their blood pressure would fall by 7.11/3.88 mmHg, on average.
As salt is associated with heart attack and strokes, researchers also calculated that:
- reducing a high salt intake by 3g/day (a good achievement) would reduce the risk of stroke by 13% and of a heart attack by 10%
- reducing salt intakes down to no more than 6g per day (better) would double this benefit
- reducing salt intakes down to no more than 3g daily (best) would potentially triple these benefits, reducing the risk of a stroke or heart attack by a third.
How to cut back on salt
Avoid adding table salt to food during cooking, and NEVER put a salt cellar on the dining table. Researchers have found that just these two simple steps can reduce blood pressure by at least 5mmHg.
Avoid obviously salty foods such as crisps, bacon, salted nuts, fish or meats that have been cured with salt and products canned in brine. Even meat pastes, patés, stock cubes and yeast extracts have a high salt content and are best avoided.
As most dietary salt comes from processed, tinned and ready-prepared foods, it’s important to check labels to identify their salt content.
If the label gives salt content as ‘sodium’, simply multiply by 2.5 to obtain the salt (sodium chloride) content. For example, a product containing 0.4g sodium actually contains 1g salt (sodium chloride – calculated by multiplying 0.4 by 2.5).
A good rule of thumb is that, per 100g food (or per serving if a serving is less than 100g):
0.5g sodium or more is a lot of sodium
0.1g sodium or less is a little sodium
A typical microwave meal contains around 5g salt, a bowl of breakfast cereal gives 1g and a bowl of canned soup has 2g, so it is easily for salt intake to mount up.
Compare brands and select those with the lowest salt content – or make your own equivalent at home with no added salt.
Be kind to your taste buds
Once your taste buds are used to highly salted foods, it takes at least one month for salt receptors on your tongue to readjust and start detecting lower salt concentrations.
During this time, foods may taste bland. Don’t be tempted to add salt – use freshly-ground black pepper, herbs and spices for flavour instead.
Adding lime juice to food can also decreases the concentration at which your taste-buds can detect salt.
Stick with it, and soon you will start to notice increased flavour in your foods.
The importance of potassium
If salt is essential for a recipe, use mineral-rich rock salt rather than table salt, or use a low-sodium, higher-potassium brand of salt sparingly.
Potassium helps to flush excess sodium from the body via the kidneys, and a diet that is lacking in potassium is linked with a higher risk of high blood pressure and stroke, especially if your diet is also high in sodium.
In one study, people taking medication for high blood pressure were able to reduce their drug dose by half (under medical supervision) just by increasing the potassium content of their food.
Good sources of potassium include seafood, fresh fruit, vegetables, juices and wholegrains.
If your blood pressure is raised, self-monitoring is key to maintaining good control.
Click here for advice on choosing a blood pressure monitor to use at home.
Image credits: novelo, starman963, tiger images / shutterstock