salt

Salt

The body has an essential requirement for salt (sodium chloride). All body fluids contain salt including blood and it has an important function in maintaining fluid balance within the body. It is also necessary in generating electrical impulses in nerve and muscle and in generating gradients across cells to enable uptake of nutrients.

It is essential for life that the concentrations of sodium and chloride in the blood are maintained within close limits. As excess salt in the diet is readily absorbed, control of sodium in the blood is achieved by excretion through the kidneys into the urine. There is also variable loss though sweat. Salt requirements are closely related to water requirements, and in extreme circumstances too low an intake results in muscular cramps. This can occur after strenuous exercise or in hot climates. People suffering from renal disease and very young infants cannot tolerate high sodium intakes because their kidneys cannot excrete the excess.

Salt has been used as a preservative and a flavouring agent for many years. Sodium in the diet is mainly from processed foods where salt has been added or where salt has been added during cooking or at the table. Sodium is also present in additives such as monosodium glutamate and sodium bicarbonate, and in some medicinal products e.g. antacids.

Sodium and chloride are comparatively low in all foods, which have not been processed. For example, salt is low in pork and other unprocessed meats but high in bacon, sausages and other meat products; low in herrings but high in kippers. Salt is also added to most canned vegetables, most butter, margarine and spreads, cheese, bread, many savoury snack foods and some breakfast cereals. Salt is added to these foods to enhance flavour but also to inhibit microbial growth. The addition of salt during bread manufacture has a beneficial effect on wheat gluten and the subsequent rising process.

The average sodium intake by adults is 3.5 g per day (equivalent to 9 g of salt) and is well above the amount needed to maintain normal functions in a temperate climate. The RNI (recommended nutrient intake) for sodium is only 1.6 g per day, but such a low intake would make the diet unpalatable, particularly as we are so used to a higher intake. The link between salt intake and blood pressure is controversial, with strong views on both sides of the debate. High blood pressure is associated with an increased risk of diseases such as coronary heart disease and stroke. In those people who already have high blood pressure, a reduced salt intake can help lower it, but this does not necessarily make it causative. However, there is a stronger link between salt intake and high blood pressure in the obese. There are many factors which affect blood pressure such as being overweight or having a high alcohol intake.

A reduction in salt intake from 9 g per day to 6 g per day is recommended by the Department of Health in the COMA report on Aspects of Cardiovascular Disease. A reduction would have a greater effect in reducing blood pressure in older people and those with high blood pressure.

Practical recommendations to reduce blood pressure include maintaining ideal body weight, keeping to sensible drinking limits, taking regular exercise, including plenty of fruit and vegetables in the diet and low fat dairy products as they provide potassium and calcium respectively and these minerals are thought to have a beneficial effect and avoiding high intakes of excessively salty foods and seasoning.

Recently, some retailers have announced their intention to reduce the salt content of many products across the range they sell. The food industry has the difficulty of reducing the salt content safely and successfully when salt acts as a preservative. However, they have announced a voluntary review of salt in manufactured products.

In the recent Government White Paper: Our Healthier Nation a target has been set to reduce the amount of salt in people's diet so helping to reduce the number of strokes and heart disease. The Government will work with the food industry to explore the number of ways to reduce salt in processed foods.