SALT – HOW MUCH IS HEALTHY?

During the past century, the evidence for the risks imposed on human health by excess salt consumption have become compelling.Salt contains both sodium and chlorine, and is chemically known as “sodium chloride”. It is the sodium part of salt that is important. The terms salt and sodium are often used synonymously, however, on a weight basis, salt comprises 40% sodium and 60% chloride. Salt is commonly used to flavour and preserve foods.

However, in recent times most of the salt eaten comes from processed and packaged foods such as sauces, processed meats and stock cubes. Increased reliance on restaurants, fast foods, and commercially prepared convenience foods has contributed greatly to a high salt intake. Highly processed, convenience foods are known to contain large quantities of salt to optimize storage stability and flavour acceptability.

Salt is the major source of sodium in the diet; therefore, in practical terms, any recommendation for sodium reduction will translate into salt reduction. The key evidence for the association between high dietary intakes of salt and blood pressure relates to sodium.

Role and Regulation of Salt in Our Body
Sodium helps to maintain the concentration of body fluids at correct levels. Sodium also aids in nerve impulse conduction and muscle contraction control. Sodium is readily absorbed from the intestines and carried to the kidneys, where it is filtered and returned to the blood to maintain appropriate levels. The amount absorbed is proportional to the intake.

The kidney is the primary organ that regulates sodium levels in the body. It responds appropriately to a wide range of sodium intakes. The capacity of the kidney to regulate the sodium content of the body varies with a number of factors, including age. For example, both the very young and the old have a decreased capacity for salt excretion. Some population groups may also have a reduced capacity from an earlier age which may be genetic, or a consequence of their habitual dietary consumption during early life.

A restriction in sodium consumption to a level below the requirement induces physiological changes leading to the active retention of sodium in the body, mainly by the kidney. However in an abrupt and sustained increase in dietary salt intake, the exceeding requirements are excreted in to maintain the sodium content of the body. However, there is an upper limit to the rate at which sodium can be lost from the body. Intakes beyond this point cause an increase in sodium content, which in turn causes water to be retained. Short term adjustments may not be manifested but at very high levels of prolonged sodium intake the kidneys' ability to maintain sodium balance begins to falter. One important manifestation may be the development of higher blood pressure.

Recommended Amount
There is a common misperception that only certain people should reduce their salt intake and that for the vast majority of the population salt reduction is unnecessary. On the other hand population based intervention studies and randomized controlled clinical trials have shown that it is possible to achieve significant reductions in blood pressure with reduced salt intake in people with and without hypertension.

International recommendations state that average adult population salt intake should be about 5-6 grams (1 teaspoonful / 2300mg of sodium) per day. The maximum for one- to three-year-olds is 2gm a day, for four- to six-year-olds it is 3gm a day, for seven- to 10-year-olds it is 5gm a day and for 11 and over it is 6gm a day. Babies should never be given extra salt on their food. However, people with hypertension or those with, or at risk of, cardiovascular disease should reduce their salt intake to less than 4g (two-thirds of a teaspoon) a day. Unfortunately most adult populations around the world have average intake of salt between 9g and 10g a day.

Experts estimate that if average consumption was cut to 6g a day it would prevent 70,000 heart attacks and strokes a year.

Health Issues
The body retains too much water and the volume of bodily fluids increases when the levels of sodium are too high. This process is linked to high blood pressure, or hypertension, which in turn is associated with a greater risk of heart disease and stroke.

In addition the resultant high levels of fluid circulating through the brain could expose the weaknesses in the brain's blood vessels and there is a greater chance that it may burst, causing a stroke.

Similarly, the large volume of fluid passing through the heart can place an unnecessary strain on the organ, increasing the possibility of heart disease.

Sodium-rich Foods and Items
The main sources of high levels of salt in our diet include salted fish – 'koobi', 'momoni' and 'kako' and salted meat - pigs' feet and salted beef. The ratio of salt to meat in these food items is usually 3:10. In simple terms, 1 small match box size (about 25g) of any of the above foods could contain about 7.5g of salt. It will therefore be prudent to limit or soak heavily salted meat or fish for at least a day prior to use in clean, cold water. The water must be replaced regularly by clean, fresh water. If the fish or meat is very salty it can also be slowly heated in water until just before boiling.

Stock cubes are also rich sources of sodium. An average size stock cube (10g) contains about 4.5g of salt. Other high sources of sodium include tomato sauce, canned beef, cheese and bacon.

It is advisable to limit the intake of the above foods to maintain healthy sodium levels.

Minimizing Sodium Levels
People can limit their salt intake by purchasing “no added salt” or “low salt” foods in the supermarket. Reading food labels can be confusing as they often give the sodium (usually in mg; 1g=1000mg), rather than the salt content of food. To calculate the amount of salt in a product, multiply the sodium content by two-and-a-half times.

Other ways people can lower the amount of salt they eat include: flavouring foods with natural herbs and spices instead of stock cubes, limiting take-away foods and eating more fruits and vegetables - they contain potassium which balances the effect of salt on the body.

One rule of thumb is to control excess salt intake for susceptible people (older, or obese and have hypertension, diabetes mellitus, lower plasma renin levels or a family history of salt-sensitivity) is to avoid adding salt the main food item- rice , banku etc. but just enough to the sauce or soup to taste.

It is appropriate to seek medical nutrition advice when managing hypertension.

The writer is a dietician, [email protected]