© Borgis - New Medicine 2/2006, s. 30-34
Sylwia Merkiel, Wojciech Chalcarz
Modifying salt intake to prevent hypertension
Department of Food and Nutrition, University School of Physical Education, Poznań, Poland
Head of Department: Prof. Wojciech Chalcarz, MD, PhD
Reduction in salt intake is one of the methods of effective prevention of hypertension epidemic. The surest way to attain this aim is to introduce the National Hypertension Prevention Programme, which should include both population strategy, aimed at the whole society, and individual strategy, aimed at a single person. Putting the knowledge on salt preferences into practice ought to play a vital role.
For 5 million years our predecessors were on a completely salt-free diet. Their organisms got used to regulate water balance and electrolyte equilibrium with the minimum amounts of salt naturally contained in food. Adding salt to food began 5-10 thousand years ago. Because the human organism was accustomed to save salt whose supply had been relatively little, the sudden – considering evolution – increase in its intake resulted in problems in the excretion of its excess. It resulted in a common blood pressure increase .
Currently, salt plays a very important role for human feeding behaviours. It influences the taste of products and dishes [2, 3], delivers sodium and chloride ions necessary to keep the systemic electrolyte equilibrium  and brings a lot of trace elements needed by the human [5, 6], provided he/she consumes non-refined salt. In a majority of countries salt is enriched with iodine. It is also considered to enrich it with iron . Salt is also commonly used by food industry engineers [3, 7, 8] as a preservative and product taste improver .
Today, salt intake is higher by 10-20 times than it was 5-10 thousand years ago. The human body is genetically pre-programmed for salt intake at the amount of 1 g per day , while in contemporary world its intake is several or even more than ten times higher .
If salt was neutral to human body, then both feeding behaviours concerning this food stuff and using it by food producers could be described only as a sociological phenomenon. However, salt is a biologically active ingredient and consequently, non-neutral to our body and health. Despite many studies concerning this problem, many people do not realize the impact of salt on human organism and the necessity to reduce its intake.
The aim of this paper was to present the connection between salt intake and hypertension and showing the possibilities to fight against this disease by reducing its consumption.
Salt intake and hypertension
A diet containing the high amount of sodium increases the blood pressure, while abusing salt leads to hypertension [9, 10, 11, 12, 13]. Hypertension causes strokes and myocardial infarctions [14, 15, 16]. Diets rich in vegetables, fruit and low-fat dairy products, i.e. recommended in the prevention of hypertension, but at the same time containing a large amount of salt results in keeping blood pressure on a higher level than while using the same diet with low salt content [17, 18]. Reducing salt intake usually results in blood pressure drop, thus reducing the risk of stroke or myocardial infarction [19, 20, 21, 22, 23, 24, 25, 26, 27]. Decreasing salt intake by 3 g/24h resulted in systolic pressure drop by 3.6 to 5.6 mmHg in patients with hypertension and by 1.8 to 3.5 mmHg in healthy persons, whereas diastolic pressure by 1.9 to 3.2 mmHg and by 0.8 to 1.8 mmHg in hypertensive and normotensive persons, respectively . This effect can be doubled by reducing salt intake by 6 g/24h, and even tripled by reducing intake by 9 g/24h . The positive effects of salt intake reduction are especially clear in persons aged 50 to 65. In this age group the reduction in salt intake by 3 g per day caused an average drop in systolic blood pressure by as much as 10 mmHg .
Reducing salt intake can contribute to considerable improvement in people health condition. Scientists found that if in the scale of whole population pressure drop amounted to 2 mmHg, it would result in the drop in hypertension incidence by as many as 17% . Reducing sodium intake by 100 mmol/day can prevent as many as 20% of hypertension incidents . It is estimated that reducing salt intake in the UK by 9 g/day would decrease the incidence of stroke by 1/3, whereas the incidence of ischaemic heart disease would drop by approximately 1/4, which would prevent 52 thousand deaths per year caused by those diseases .
It should be kept in mind that reducing blood pressure by applying drug treatment provided comparable effects to changes resulted from reducing salt intake [13, 29], which shows that low-salt diet has an important role in preventing and treating hypertension . When it is impossible to eliminate drugs completely, a proper diet can effectively support the pharmacological treatment of hypertension. In aged persons reducing sodium intake by only 40 mmol/day resulted in 30 percent drop in the demand for drugs . It should be noted that pharmacological treatment can be far more effective if it is accompanied by non-pharmacological treatment: reduction in salt intake, physical exercise and body mass reduction .
The reduction of salt intake brings also some financial benefits . Reducing daily consumption of salt by 6 g per person in the population of Norwegians would bring the society 118 million dollars of savings as a result of decrease in treatment expenses .
The problem of salt intake amount in social, economic and medical context cannot be omitted in Poland either. In 2001 we consumed 9.21 g of salt per person per day , while levels defined by WHO show that its daily intake should not exceed 6 g . Studies performed in our Department show that average salt consumption by persons living in old age homes in Wielkopolska amounted to almost 10 g/day , whereas pre-school (kindergarten) children from Nowy Sącz exceeded 7 g/day. These results are really alarming especially in the case of children who according to the recommendations of Consensus Action on Salt and Heath  should not take more than 3 g/day. These limits were exceeded considerably also in the studies on Polish teenagers [37, 38], students [39, 40] and the aged [35, 41, 42]. As it is clearly seen, the problem refers to the whole Polish population irrespective of age and results from deeply rooted, passed from generation to generation bad feeding habits. It is estimated that as many as 46 percent of men and 36 percent of women suffer from hypertension . Every year about 70 thousand people in Poland die of stroke, whereas about 100 thousand die of myocardial infarction . Therefore, the reduction of salt intake in Poland is really necessary.
Methods of salt intake reduction in population-based and individual approach
In order to reduce salt intake throughout Poland, it would be necessary to create, similarly as the National Cholesterol Prophylaxis Programme , the National Hypertension Prevention Programme. It should include a population strategy aimed at the entire society and an individual strategy aimed at single persons.
The aim of the population strategy would be to decrease the incidence of hypertension in the entire population. To achieve this, it would be necessary to promote the reduction of salt intake as well as to introduce some legal restrictions concerning the use of salt in food products by producers and encouraging them, first of all by financial impulses, to produce low-sodium food. It would be important to impose the obligation to indicate saltiness on the labels of salt, as its saltiness depends on its chemical composition. It should be also important to promote physical activity and indicate the importance of avoiding obesity .
Without the above-mentioned legal regulations concerning salt content in products and meals, it would not be possible to reduce salt intake, as salt added by people while eating or preparing dishes is only a fragment of total salt consumption. The majority of salt comes from factory prepared products and dishes salted during their production process [46, 47, 48, 49]. It is estimated that in Western European populations the salt consumed with everyday food in 75-80% comes from ready made food products . Large amounts of salt are added to fast food type products or any sorts of powdered instant soups and sauces. In today´s ”busy” society these products are very popular because of time saving and we are encouraged to use them by ubiquitous advertisements that have an extremely strong impact on children [50, 51, 52]. In addition, the salt supply is increased by basic food products, being present in everyday human diet such as for example bread [34, 53].
Many producers explain their objection to salt reduction in their products by the anxiety of making them less popular among customers and as a result, sales drop. Although, the truth is that producers add salt to food products because of its ability to bind water (hygroscopic properties)[3, 54]. Thanks to this, it is possible to cheaply increase the product weight. In addition, the more salt consumed the more beverages drunk and this is probably the reason why some non-alcoholic beverages producers are also the owners of companies producing salty snacks .
The studies performed show that reducing salt content will not result in any reduction of customer acceptance for products and consequently, sales drop. Researchers observed that decreasing the sodium content in white bread by 25% did not reduce customer acceptance for this product . Taste assessment did not differ much among persons tasting bread with salt content lower by 10% and 20% . Similar results were obtained in the studies concerning taste values and customer acceptance for soups with various salt content, sodium monoglutamate and calcium diglutamate. The studies showed that soups with salt content reduced both to 60% and to 30%, but supplemented by calcium diglutamate received the same or higher marks in terms of preferences and taste richness, intensity and natural values as soups with standard salt content .
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