When blood pressure is chronically elevated, the condition is referred to as hypertension (HTN). In 90% of hypertension cases, the cause is unknown, and the condition is called essential, or primary, hypertension. The other 10% of cases are classified as secondary hypertension because another underlying problem causes the condition. Some causes of secondary hypertension include kidney disease, problems of the adrenal glands, and use of oral contraceptives.

The blood pressure commonly measured is that of the artery in the upper arm. This measurement is made with an instrument called the sphygmomanometer. The top number represents the systolic pressure, which is measured when the heart contracts. The lower number represents the diastolic pressure, measured when the heart is at rest. The pressure is measured in millimetres of mercury (mm Hg). Hypertension can be diagnosed when, on several occasions, the systolic pressure is 140 mmHg or higher and the diastolic pressure is 90 mmHg or higher. The blood pressure categories are the following:

• Normal—less than 120/less than 80 mm Hg
• Prehypertension—120–139/80–88 mm Hg
• Stage 1 hypertension—140–159/90–99 mm Hg
• Stage 2 hypertension—160/100 mm Hg

Hypertension contributes to heart attack, stroke, heart failure, and kidney failure. It is sometimes called the silent disease because sufferers can be asymptomatic (without symptoms). Its frequency increases with age, and it is more prevalent among African Americans than others.

Heredity and obesity are predisposing factors in hypertension. Smoking and stress also contribute to hypertension. Weight loss usually lowers blood pressure, and, consequently, clients are often placed on weight-reduction diets.

Excessive use of ordinary table salt is also considered a contributory factor in hypertension. Table salt consists of over 40% sodium plus chloride. Both are essential for maintaining fluid balance and, consequently, blood pressure. When consumed in normal quantities by healthy people, they are beneficial. When the fluid balance is upset, sodium and fluid accumulate in body tissue, causing oedema, which places extra pressure on the blood vessels. A sodium-restricted diet, often accompanied by diuretics, can be prescribed to alleviate this condition. When the sodium content in the diet is reduced, the water and salts in the tissues flow back into the blood to be excreted by the kidneys. In this way, the oedema is relieved. The amount of sodium restricted is determined by dietitians based on the patient’s condition.

Previous research focused primarily on sodium as a primary factor in the development of hypertension, but as research continues, the effects of chloride are also receiving increasing scrutiny. Additionally, the specific roles of calcium and magnesium in relation to hypertension are being investigated.

Knowing that sodium raises blood pressure and potassium lowers it, the NIH (National Institutes of Health) created the DASH (Dietary Approaches to Stop Hypertension) eating plan. The DASH plan has been clinically shown to reduce high blood pressure while increasing the serving of fruits and vegetables to 8 to 12 servings per day, depending upon calorie intake. Described by a dietitian.

Many fruits and vegetables are high in potassium, which can help lower blood pressure. The latest guideline for potassium intake is 4.7 grams, or 4,700 milligrams, per day to help lower blood pressure. It is recommended that a Dietitian be consulted if the DASH eating plan is undertaken and one is already on blood pressure–lowering medication.

DIETARY TREATMENT FOR HYPERTENSION

As indicated above, weight loss for the obese patient with hypertension usually lowers blood pressure, and thus a calorie-restricted diet might be prescribed. A sodium-restricted diet is frequently prescribed for clients with hypertension. Certain ethnic groups, such as African Americans with a new onset of HTN and those already diagnosed with HTN, should limit sodium intake to 1,500 mg/day.

When diuretics are prescribed in conjunction with a sodium-restricted diet, the patient may lose potassium through the urine and, therefore, be advised to increase the intake of potassium-rich foods in their diet.

Sodium-Restricted Diets

A sodium-restricted diet is a regular diet in which the amount of sodium is limited. Such a diet is used to alleviate oedema and hypertension. Most people obtain far too much sodium from their diets. It is estimated that the average adult consumes 7 grams of sodium a day. A committee of the Food and Nutrition Board recommends that the daily intake of sodium be limited to no more than 2,300 mg (2.3 grams), and the Board itself set a safe minimum at 500 mg/day for adults.  Sodium is found in food, water, and Medicine. It is impossible to have a diet totally free of sodium. Meats, fish, poultry, dairy products, and eggs all contain substantial amounts of sodium naturally. Cereals, vegetables, fruits, and fats naturally contain small amounts of sodium. Water contains varying amounts of sodium. However, sodium is often added to foods during processing, cooking, and at the table. The food label should indicate the addition of sodium to commercial food products. In some of these foods, the addition of sodium is evident because it can be tasted, as in prepared dinners, potato chips, and canned foods. In others, it is not. The following are examples of sodium-containing products that are frequently added to foods and may not be readily noticeable by the consumer.

• Salt (sodium chloride)—used in cooking or at the table and in canning and processing.
• Monosodium glutamate (called MSG and sold under several brand names)—a flavour enhancer used in home, restaurant, and hotel cooking and in many packaged, canned, and frozen foods.
• Baking powder—used to leaven quick breads and cakes.
• Baking soda (sodium bicarbonate)—used to leaven breads and cakes; sometimes added to vegetables in cooking or used as an “alkalizer” for indigestion.
• Brine (table salt and water)—used in processing foods to inhibit the growth of bacteria; in cleaning or blanching vegetables and fruits; in freezing and canning certain foods; and for flavour, as in corned beef, pickles, and sauerkraut.
• Disodium phosphate—present in some quick-cooking cereals and processed cheeses.
• Sodium alginate—used in many chocolate milks and ice creams for smooth texture.
• Sodium benzoate—used as a preservative in many condiments such as relishes, sauces, and salad dressings.
• Sodium hydroxide—used in food processing to soften and loosen skins of ripe olives, hominy, and certain fruits and vegetables.
• Sodium propionate—used in pasteurised cheeses and in some breads and cakes to inhibit the growth of mould.
• Sodium sulfite—used to bleach certain fruits in which an artificial colour is desired, such as maraschino cherries and glazed or crystallised fruit; also used as a preservative in some dried fruit, such as dried plums.

Because the amount of sodium in tap water varies from one area to another, Softened water always has additional sodium. If the sodium content of the water is high, the hypertensive patient may have to use bottled water.

Some over-the-counter medicines contain sodium. A hypertensive patient on a sodium-restricted diet should obtain the dietitian’s permission before using any salt substitute. Many salt substitutes contain potassium, which can affect the heartbeat. The amount of sodium allowed depends on your condition and is prescribed by your dietitian. In extraordinary cases of fluid retention, a diet with 1 gram of sodium per day can be prescribed. A very low restriction limits sodium to 2 grams a day. A moderate restriction limits sodium to 3 to 4 grams a day.

Adjustment to Sodium Restriction

Sodium-restricted diets range from “different” to “tasteless” because most people are accustomed to salt in their food. It can be challenging for patients to understand the necessity of following such a diet, particularly if it must be adhered to for the remainder of their lives. If your dietitian allows, it will help you adjust if the sodium content of the diet can be reduced gradually.

It is also helpful to use a variety of herbs, spices, and flavourings that are allowed on sodium-restricted diets.