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Nutrition and Blood Pressure
Source: Cyberounds
December 13, 2001
Introduction
Most of the epidemiological studies which have shown a strong relationship between salt intake and blood pressure have been done in very heterogeneous populations - people living in the United States or Europe have been compared with populations living in very remote areas, such as the Yanomani Indians in Brazil or populations in Papua, New Guinea. These studies demonstrate considerable differences in blood pressure as a function of sodium intake. However, if you look at more homogeneous populations, you find a much smaller, or often no relationship, between salt intake and blood pressure.
Salt sensitivity
We do know, nevertheless, that some individuals given a higher salt intake react with an increase in blood pressure, the so-called concept of "salt sensitivity." In salt sensitive people, the blood pressure natriuresis curve is shifted to the right, towards higher blood pressure values; this is probably secondary to hormonal changes, especially alteration in the renin-aldosterone system. It is important to remember that it is the salt sensitivity and not the sodium in the diet that leads to an increase in blood pressure.
In daily practice, several clinical signs and constellations are suggestive for salt sensitivity.
Factors Associated with Salt-Sensitivity:
Female gender
Age
Obesity (abdominal obesity)
Alcoholism
African-American origin
Level of blood pressure
Isolated systolic hypertension (ISH)
Low renin hypertension (hypertensive patients with a low plasma renin activity)
Impaired glucose tolerance
Diabetes
Renal insufficiency
Positive family history of hypertension
(Higher) microalbuminuria
As a general rule, about 30% of normotensive subjects are salt sensitive, whereas at least 50% of hypertensive subjects have to be regarded as salt sensitive. In African-Americans, up to 75% of hypertensive subjects are salt-sensitive. As a general rule, it is important to remember that the absolute level of blood pressure is an important determinant of salt sensitivity. The higher the blood pressure, the higher the probability of salt sensitivity.
Reducing salt intake
In most acculturated populations, the salt intake varies between 8-15 g/d. According to data from NHANES III, the current sodium intake in the U.S. population (including all ages and races) is 3289 mg/d, which corresponds to 8.3 g salt/d. 1 g NaCl (salt) contains 393 mg sodium. The highest salt intake of 12.5 g/d was found in young, non-Hispanic, African-American men aged 16-19 years.
Up to 30-50% of the salt may be added at the table and could thus be directly influenced by the consumer. Instead of salt, it is advised to use fresh or dried herbs without added sodium as major condiments. (The use of potassium containing salt substitutes would also be an option, which is, however, not our favorite alternative, since there may be a risk for hyperkalemia in certain patients - for example, hypertensive patients with renal insufficiency or patients on potassium-sparing diuretics.) In addition, the reduction of sodium-containing processed foods is advised. An optimal blood pressure lowering effect can be obtained by dietary strategies, as propagated by the so-called DASH diet (see below).
Non-smoking is a must, as smoking has very strong immediate pressor effects. It is evident that these strategies are implemented stepwise. In clinical practice, it is very important to carefully select the most promising strategy for a given patient, otherwise the patient might be completely overwhelmed and unable to follow any advice.
According to the present guidelines, the implementation of non-pharmacological strategies should be done for a period of 3 to 6 months. Since this is often difficult to implement, we advise patients to restrict intake for a period of 2-3 weeks with "total compliance" and most patients are able to do so. A significant fall of blood pressure after such a short-term sodium restriction - especially in the presence of risk factors for salt sensitivity - is very suggestive for salt sensitivity.
How far should sodium intake be reduced? The ideal amount of the sodium reduction in a salt sensitive subject is not known but we believe that any reduction is better than none. The severity of salt restriction depends on the clinical setting, i.e. the degree of blood pressure control needed.
In view of the loss of palatability of food, if sodium intake is reduced stepwise, patients will become accustomed to the altered taste and often an impressive reduction of sodium intake can be achieved. The concomitant improvement of blood pressure may function as a motivator for compliance.
The mediation of taste is an important function of sodium in our diet. With increasing age, the normal taste perception declines and the "hunger for salt" may increase to make food more tasty and palatable. Especially in the elderly, who already have a reduced appetite, extreme sodium restriction may be counterproductive by reducing food intake.
The role of potassium
Evidence suggests strongly that an increase in potassium intake may be even more important than sodium restriction for blood pressure. Ideally, the different nutritional factors which might have an effect on blood pressure should be also be part of the program: controlling body weight (especially abdominal obesity), moderate any alcohol intake, increase daily physical activity and, last but not least, stress control.
Many epidemiological and interventional studies have shown that potassium has a rather strong blood pressure lowering effect, especially in salt sensitive subjects. Most studies suggest that the ratio of sodium to potassium is of crucial importance. Potassium may lower blood pressure by "antagonizing" some of the sodium effects.
Potassium, also, has a rather strong natriuretic effect and further inhibits renin release. Potassium intake should be increased by the consumption of foods rich in potassium and not by supplements. Potassium supplements might lead to a dangerous hyperkalemia. Fruits and vegetables, as well as skim milk and milk products, are good sources of potassium. As long as food is not processed, all potassium rich foods are low in sodium.
In some "special" patients, however, we do not favor salt substitutes for several reasons. First, salt substitutes are not usually associated with an overall awareness about changing dietary habits. Second, salt substitutes do not necessarily increase palatability since they have a somewhat bitter aftertaste. Third, and very important, salt substitutes may represent an important source of large amounts of potassium. In subjects with renal insufficiency, the risk of hyperkalemia should not be neglected.
Other dietary measures
Observational and interventional studies have reported blood pressure lowering effects of calcium. As compared to other nutrients, the blood pressure lowering effects of calcium were rather low and inconsistent. However, calcium in combination with potassium, magnesium and moderate sodium restriction may have greater importance. So we recommend to patients a regular daily consumption of low fat milk products, such as 1 to 2 glasses of skim milk per day or a skim milk yogurt per day.
An adequate magnesium intake, according to the present guidelines, is essential. However, any increase of magnesium by dietary means or supplements alone has not produced an effect on blood pressure.
Alcohol intake
Alcohol is probably the most important pressor agent in daily practice. Most of our hypertensive patients, especially the ones who are difficult to treat, often report an excessive alcohol intake. There is no single mechanism by which alcohol increases blood pressure. There seems to be a dose dependency - low to moderate (up to 2 drinks/day) alcohol intakes are not associated with increased blood pressure. Because of alcohol-induced liver pathology, antihypertensive drugs are differently metabolized, so that they are less effective, requiring larger dosages that are more likely to produce side effects.
There is a strong relationship between the frequency of alcohol intake and the absolute amount of alcohol consumed. Accordingly we try not to forbid alcohol completely, which would be an unrealistic strategy; however, we try to convince our patients not to drink daily.
Women have a lower so-called first pass metabolism of alcohol in the gastric mucosa. It is conceivable that the alcohol-blood pressure relationship for a certain dose may be stronger in women. This would be of importance at low to moderate levels of intake; however, in heavier consumers the gender difference in alcohol metabolism is not seen.
Caffeine intake
In a person who never consumes caffeine, blood pressure increases upon the ingestion of a cup of coffee or a cup of espresso. However, in regular coffee drinkers, you don't see a blood pressure increasing effect of coffee consumption. So, in daily practice, it is not necessary to advise coffee-drinking hypertensive patients to cut down their coffee consumption.
Source: Cyberounds
December 13, 2001
Introduction
Most of the epidemiological studies which have shown a strong relationship between salt intake and blood pressure have been done in very heterogeneous populations - people living in the United States or Europe have been compared with populations living in very remote areas, such as the Yanomani Indians in Brazil or populations in Papua, New Guinea. These studies demonstrate considerable differences in blood pressure as a function of sodium intake. However, if you look at more homogeneous populations, you find a much smaller, or often no relationship, between salt intake and blood pressure.
Salt sensitivity
We do know, nevertheless, that some individuals given a higher salt intake react with an increase in blood pressure, the so-called concept of "salt sensitivity." In salt sensitive people, the blood pressure natriuresis curve is shifted to the right, towards higher blood pressure values; this is probably secondary to hormonal changes, especially alteration in the renin-aldosterone system. It is important to remember that it is the salt sensitivity and not the sodium in the diet that leads to an increase in blood pressure.
In daily practice, several clinical signs and constellations are suggestive for salt sensitivity.
Factors Associated with Salt-Sensitivity:
Female gender
Age
Obesity (abdominal obesity)
Alcoholism
African-American origin
Level of blood pressure
Isolated systolic hypertension (ISH)
Low renin hypertension (hypertensive patients with a low plasma renin activity)
Impaired glucose tolerance
Diabetes
Renal insufficiency
Positive family history of hypertension
(Higher) microalbuminuria
As a general rule, about 30% of normotensive subjects are salt sensitive, whereas at least 50% of hypertensive subjects have to be regarded as salt sensitive. In African-Americans, up to 75% of hypertensive subjects are salt-sensitive. As a general rule, it is important to remember that the absolute level of blood pressure is an important determinant of salt sensitivity. The higher the blood pressure, the higher the probability of salt sensitivity.
Reducing salt intake
In most acculturated populations, the salt intake varies between 8-15 g/d. According to data from NHANES III, the current sodium intake in the U.S. population (including all ages and races) is 3289 mg/d, which corresponds to 8.3 g salt/d. 1 g NaCl (salt) contains 393 mg sodium. The highest salt intake of 12.5 g/d was found in young, non-Hispanic, African-American men aged 16-19 years.
Up to 30-50% of the salt may be added at the table and could thus be directly influenced by the consumer. Instead of salt, it is advised to use fresh or dried herbs without added sodium as major condiments. (The use of potassium containing salt substitutes would also be an option, which is, however, not our favorite alternative, since there may be a risk for hyperkalemia in certain patients - for example, hypertensive patients with renal insufficiency or patients on potassium-sparing diuretics.) In addition, the reduction of sodium-containing processed foods is advised. An optimal blood pressure lowering effect can be obtained by dietary strategies, as propagated by the so-called DASH diet (see below).
Non-smoking is a must, as smoking has very strong immediate pressor effects. It is evident that these strategies are implemented stepwise. In clinical practice, it is very important to carefully select the most promising strategy for a given patient, otherwise the patient might be completely overwhelmed and unable to follow any advice.
According to the present guidelines, the implementation of non-pharmacological strategies should be done for a period of 3 to 6 months. Since this is often difficult to implement, we advise patients to restrict intake for a period of 2-3 weeks with "total compliance" and most patients are able to do so. A significant fall of blood pressure after such a short-term sodium restriction - especially in the presence of risk factors for salt sensitivity - is very suggestive for salt sensitivity.
How far should sodium intake be reduced? The ideal amount of the sodium reduction in a salt sensitive subject is not known but we believe that any reduction is better than none. The severity of salt restriction depends on the clinical setting, i.e. the degree of blood pressure control needed.
In view of the loss of palatability of food, if sodium intake is reduced stepwise, patients will become accustomed to the altered taste and often an impressive reduction of sodium intake can be achieved. The concomitant improvement of blood pressure may function as a motivator for compliance.
The mediation of taste is an important function of sodium in our diet. With increasing age, the normal taste perception declines and the "hunger for salt" may increase to make food more tasty and palatable. Especially in the elderly, who already have a reduced appetite, extreme sodium restriction may be counterproductive by reducing food intake.
The role of potassium
Evidence suggests strongly that an increase in potassium intake may be even more important than sodium restriction for blood pressure. Ideally, the different nutritional factors which might have an effect on blood pressure should be also be part of the program: controlling body weight (especially abdominal obesity), moderate any alcohol intake, increase daily physical activity and, last but not least, stress control.
Many epidemiological and interventional studies have shown that potassium has a rather strong blood pressure lowering effect, especially in salt sensitive subjects. Most studies suggest that the ratio of sodium to potassium is of crucial importance. Potassium may lower blood pressure by "antagonizing" some of the sodium effects.
Potassium, also, has a rather strong natriuretic effect and further inhibits renin release. Potassium intake should be increased by the consumption of foods rich in potassium and not by supplements. Potassium supplements might lead to a dangerous hyperkalemia. Fruits and vegetables, as well as skim milk and milk products, are good sources of potassium. As long as food is not processed, all potassium rich foods are low in sodium.
In some "special" patients, however, we do not favor salt substitutes for several reasons. First, salt substitutes are not usually associated with an overall awareness about changing dietary habits. Second, salt substitutes do not necessarily increase palatability since they have a somewhat bitter aftertaste. Third, and very important, salt substitutes may represent an important source of large amounts of potassium. In subjects with renal insufficiency, the risk of hyperkalemia should not be neglected.
Other dietary measures
Observational and interventional studies have reported blood pressure lowering effects of calcium. As compared to other nutrients, the blood pressure lowering effects of calcium were rather low and inconsistent. However, calcium in combination with potassium, magnesium and moderate sodium restriction may have greater importance. So we recommend to patients a regular daily consumption of low fat milk products, such as 1 to 2 glasses of skim milk per day or a skim milk yogurt per day.
An adequate magnesium intake, according to the present guidelines, is essential. However, any increase of magnesium by dietary means or supplements alone has not produced an effect on blood pressure.
Alcohol intake
Alcohol is probably the most important pressor agent in daily practice. Most of our hypertensive patients, especially the ones who are difficult to treat, often report an excessive alcohol intake. There is no single mechanism by which alcohol increases blood pressure. There seems to be a dose dependency - low to moderate (up to 2 drinks/day) alcohol intakes are not associated with increased blood pressure. Because of alcohol-induced liver pathology, antihypertensive drugs are differently metabolized, so that they are less effective, requiring larger dosages that are more likely to produce side effects.
There is a strong relationship between the frequency of alcohol intake and the absolute amount of alcohol consumed. Accordingly we try not to forbid alcohol completely, which would be an unrealistic strategy; however, we try to convince our patients not to drink daily.
Women have a lower so-called first pass metabolism of alcohol in the gastric mucosa. It is conceivable that the alcohol-blood pressure relationship for a certain dose may be stronger in women. This would be of importance at low to moderate levels of intake; however, in heavier consumers the gender difference in alcohol metabolism is not seen.
Caffeine intake
In a person who never consumes caffeine, blood pressure increases upon the ingestion of a cup of coffee or a cup of espresso. However, in regular coffee drinkers, you don't see a blood pressure increasing effect of coffee consumption. So, in daily practice, it is not necessary to advise coffee-drinking hypertensive patients to cut down their coffee consumption.
