Hypertension

Hypertension is when blood pressure, the blood's force against the walls of the arteries, is consistently abnormally high in relation to age. It is a major public health problem that often requires long-term medication. More than one in four American adults have high blood pressure and more than 50 per cent of Americans over the age of 65 may be affected. It is the most prevalent form of cardiovascular disease and, if left untreated, can lead to heart attack, stroke and kidney disease.

 

Diagnosis of Hypertension

A normal blood pressure reading for adults is considered to be around 120/80 mmHg. The first number represents the systolic pressure (the pressure when the heart is contracting) and the second number is the diastolic pressure (the pressure when the heart is relaxed). A high blood pressure is 140/90 mmHg or above.

High blood pressure can be divided into two major categories. When high blood pressure occurs without apparent cause, it is known as primary or essential hypertension; and when it occurs because of another disease, such as poor kidney function, it is known as secondary hypertension. Anyone can have temporary high blood pressure, resulting from excitement, nervousness, exertion, anger, fatigue, cold or smoking. In hypertension, high blood pressure is sustained over a period of time.

Blood pressure tends to rise with age but hypertension can also occur in children and teenagers, with increased risk of disease later in life. Most younger sufferers have a family history of hypertension and tend to be overweight.

 

Symptoms of Hypertension

When high blood pressure is mild it usually has no symptoms. In more severe cases, it can cause headaches, fatigue, dizziness, heart palpitations, nosebleeds and blurred vision.

Causes of Hypertension

The causes of primary hypertension remain unclear, although there are several risk factors. These include heredity, diet, environmental factors, smoking, alcohol, drinking large amounts of coffee, lack of exercise, obesity and stress. Hypertension may occur due to a combination of factors, and these may vary from person to person. Hypertension is twice as common in African Americans than Caucasians. The reasons for this are not known. Hypertension is rare in cultures that are relatively untouched by the Western life-style.

 

Treatment of Hypertension

Because lifestyle plays a major role in causing and maintaining hypertension, effective treatment often involves changes in dietary, psychological and social factors. Exercise, relaxation techniques and meditation have all shown beneficial effects. In some cases, hypertension can be controlled by lifestyle changes; in other cases medications may be used.

There are several different types of drugs that are used to treat hypertension. These include diuretics, which act by forcing the kidneys to excrete water and sodium at a faster rate; and beta blockers, which lower heart rate and cardiac output. Other drugs known as ACE inhibitors affect the levels of hormones that constrict blood vessels.

Another major class of drugs used to lower high blood pressure blocks the channels which transport calcium across muscle cell membranes. There is currently an ongoing debate as to whether these calcium channel blockers increase the risk of heart attacks.

Diet and Hypertension

Because hypertension is currently a chronic incurable disease, prevention is more important than cure. Diet is strongly linked to the prevention and treatment of hypertension.

Obesity increases the risk of hypertension. About one-third of people with hypertension are overweight, and even a small decrease in weight can reduce the risk of hypertension. Many studies indicate that exercise and keeping to a reasonable weight may be the best way to control hypertension. Effective stress management, watching salt intake, limiting coffee intake and drinking alcohol in moderation may also help to prevent high blood pressure.

High intakes of fruit and vegetables seem to be linked to lower blood pressure as they contain so many beneficial nutrients. An effective diet for blood pressure reduction is low in fat, particularly saturated fat; high in essential fatty acids; low in sugar, especially refined sugar; low in cholesterol; high in fiber; low in salt and high in potassium, magnesium, calcium and vitamin C.

 

Minerals and Blood Pressure

Blood pressure is regulated by a balance of the minerals sodium, potassium, calcium and magnesium. Hypertension appears to be associated with an imbalance of these minerals where sodium and possibly chloride are too high, and potassium, calcium and magnesium are too low.

Increasing dietary intakes of potassium, calcium, and magnesium have each been reported to lower blood pressure, but the extent of blood pressure reduction in epidemiological studies and clinical trials has varied. Studies in China have shown that multivitamin and mineral supplements lower the risk of hypertension in a population with a vitamin/mineral-poor diet.1

Sodium

Epidemiological studies suggest that high sodium intakes are linked to high blood pressure. As a person ages, changes in the hormonal systems that regulate the control of water and sodium balance lead to changes in blood pressure. The evidence for the role of sodium is strongest in those subjects with impaired ability to excrete sodium because of kidney disease or hormonal abnormalities. In these cases, restriction of dietary sodium promptly lowers blood pressure. The role of sodium in causing primary hypertension is more controversial.

The Intersalt Study

Most studies find that high salt diets accelerate the increase in blood pressure that occurs with age. These include the Intersalt study, which is an international epidemiological study covering 32 countries and including 10 000 subjects. This study has shown a relationship between blood pressure and body mass index and alcohol consumption, but the data on salt has been interpreted differently by different researchers. The results suggest that dietary salt restriction has more effect on blood pressure in those aged 45 and older. In young people diet and exercise may play a more important part. Some patients with mild to moderate primary hypertension respond to moderate sodium restriction with a fall in blood pressure. This restriction also seems to reduce the amount of medication needed to keep blood pressure under control.2

Salt-Sensitivity

Some people are more susceptible than others to the blood pressure-raising effects of salt. This is known as salt-sensitivity. About 30 per cent of people and as many as 40 to 50 per cent of those suffering from hypertension may be salt-sensitive and respond favorably when salt is restricted. Salt-sensitivity is more common among certain population groups including black people, diabetics and the elderly. Reduction of salt intake is generally recommended to reduce the risk of developing high blood pressure as most Western diets are very high in salt.

A review published in 1997 in the American Journal of Clinical Nutrition showed that experimental data support the view that when adults meet or exceed the recommended dietary allowances of calcium, potassium, and magnesium, high sodium intakes are not associated with high blood pressure. Thus adequate mineral intake may protect against salt-sensitivity.3

Salt Restriction

A new study of almost 1500 British people has found that those who eat the most salt tend to have the highest blood pressure. The study, which involved men and women aged 16 to 64 found that as daily salt intakes rose from 1600 mg to 9200 mg, so did blood pressures. A rise in salt consumption from 2300 mg to 4600 mg led to a 7.1 mmHg rise in systolic blood pressure for women and a 4.9 mmHg rise for men.4

In a two-month double-blind, randomized, placebo-controlled crossover study published in 1997 in The Lancet, researchers found that modest reduction in salt in the diets of elderly people led to lower blood pressure. The study involved 29 patients with high blood pressure and 18 with normal blood pressure. The average blood pressure fall was 8.2/3.9 mmHg in the normal subjects and 6.6/2.7 mmHg in those with high blood pressure.5 In those with normal blood pressure, cutting salt may have little effect, according to an analysis of 83 studies published in the Journal of the American Medical Association in 1998.6

Dietary sodium restriction is used to control pregnancy-related high blood pressure. It does not seem to lead to any adverse effects on other minerals or the baby. In fact, increasing evidence suggests that the amount of salt in a baby's diet affects blood pressure later in life. In a study published in 1997, Dutch researchers compared the effects of low salt and normal salt diets in 476 children born in 1980. They measured blood pressures in the first week of life and every four weeks after that for a six-month period. Fifteen years later, the study participants had their blood pressures measured again and the results showed that children who had been in the low salt group had lower blood pressures than those in the normal salt group.7

Stress and Sodium

Stress may affect sodium excretion. In certain people, stress seems to contribute to high blood pressure, and this may be mediated via effects on sodium excretion. In a 1995 German study, researchers tested the effects of stress on 27 people with normal blood pressure and 21 with high blood pressure. The participants in the study took part in a 30-minute video game after which their excretion of sodium was measured. Seventy per cent of the people showed increased sodium excretion and 30 per cent showed decreased excretion. Those who excreted more sodium showed less stress-associated increases in blood pressure and greater expression of anger.8

Chloride

Some evidence indicates that when sodium is combined with chloride, it exerts greater effects on raising blood pressure than when it is combined with other compounds such as phosphate. Dietary intake of both sodium and chloride may be necessary for the development of hypertension.

Potassium

Population studies suggest that a low intake of potassium may be linked to an increase in blood pressure, and increasing potassium-rich foods in the diet can lead to a reduction in high blood pressure. The typical Western diet is low in potassium relative to sodium, and the ratio of sodium to potassium in the diet may be more important than sodium alone. Studies suggest that the most beneficial effects on blood pressure are seen when sodium intake is reduced and potassium intake is increased.

Potassium depletion causes the body to retain more fluid in response to a large dose of salt. Potassium may help to lower blood pressure in several ways, including enhancing sodium excretion, by directly dilating blood vessels, or lowering cardiovascular reactivity to body chemicals which constrict blood vessels.

Potassium supplements may be useful in the treatment of high blood pressure. Doses involved usually range from 2.5 to 5 g. In people with normal blood pressure, those who are salt-sensitive or who have a family history of hypertension appear to benefit most from potassium supplementation. The greatest blood pressure-lowering effect of potassium supplements occurs in those with severe hypertension. Beneficial effects are more pronounced with long-term supplementation.

A 1997 analysis of studies on the effects of potassium supplementation on blood pressure confirms that low intake of the mineral is linked to high blood pressure and increasing intake is a beneficial part of treatment. Researchers at Johns Hopkins University looked at 33 randomized controlled trials with over 2069 participants in which potassium supplements were used. Positive effects were seen with a decrease in mean systolic pressure of 3.11 mmHg and in diastolic pressure of 1.97 mmHg. The effects were enhanced in those exposed to a high intake of sodium.9

In a study published in 1998 in the American Heart Association journal Hypertension, researchers at the Harvard School of Public health tested the effects of potassium, calcium and magnesium supplements on 300 women (average age 39 years) whose dietary intakes of those minerals were low. The participants had blood pressure in the normal range. The women were divided into five groups: the calcium (1200 mg per day), magnesium (336 mg per day) and potassium (1600 mg per day) groups; a group who received all three supplements; and a placebo group. The result showed that potassium supplements lowered blood pressure whereas calcium and magnesium supplements did not. The results also showed that those in the three supplements group had smaller falls in blood pressure than those in the potassium group. The researchers speculate that calcium and magnesium might in some way interfere with the blood pressure-lowering effect of potassium.10

Calcium

Low dietary calcium may increase the risk of high blood pressure. Data from the US Health and Nutrition Examination Survey (NHANES I) show that hypertensive people consume 18 per cent less dietary calcium than those with normal blood pressure.11

Disturbances in calcium metabolism have been found in people suffering from primary hypertension. These include reduced blood calcium levels, increased urinary excretion of calcium, raised intracellular calcium levels, reduced cell membrane calcium binding, and other indicators of higher calcium needs. Some of these changes, however, may be secondary to blood pressure elevation. Some research suggests that alterations in calcium-regulating hormones in general, and vitamin D in particular, contribute to essential hypertension, especially salt-sensitive forms.

Researchers involved in the Dutch Hypertension and Offspring Study studied young people with normal blood pressure. Some of them had a family history of high blood pressure while others did not. The findings showed that disturbances in calcium metabolism are present in the early phase of primary hypertension and may precede the development of high blood pressure. Changes in calcium metabolism may reflect a genetic basis for calcium-sensitive hypertension.12

Increasing calcium intake has been shown to lower blood pressure in some cases. Supplemental dietary calcium may affect blood pressure by a number of mechanisms. It may affect smooth muscle cell contraction, hormone action, nervous system function and increase sodium excretion. In an eight week randomized, placebo-controlled study done in 1985 in the US, researchers assessed the effect of 1000 mg per day of calcium supplements on the blood pressure of 48 people with hypertension and 32 without. Compared with placebo, calcium significantly lowered both systolic and diastolic blood pressures, but only in those with high blood pressure.13

Whether calcium can lower blood pressure in cases where there is no apparent deficiency is not clear. Increasing calcium intake may lower blood pressure by increasing the excretion of sodium, and calcium supplements may be most useful in those who are salt-sensitive. Results from the University of Pittsburgh Trials of Hypertension Prevention (TOHP) showed calcium supplements (100 mg per day) to have little effect on blood pressure. The participants were healthy adult men and women (both white and African American) aged 30 to 54 years with high-normal diastolic blood pressure. However, the supplements did seem to lower blood pressure in white women, who are at particular risk of low calcium intakes.14 Supplements may be beneficial in cases where calcium intake is insufficient, which may be relatively common.

Pregnancy

The results of a study reported in 1997 in the British Medical Journal suggest that women who take calcium supplements in pregnancy have children with lower blood pressures. Researchers measured the blood pressures of almost 600 children of women who had previously been involved in a double-blind trial of the effects of calcium on blood pressure during pregnancy. The results showed that, overall, systolic blood pressure was lower in the calcium group, particularly among overweight children.15

Use of calcium supplements during pregnancy may lower a woman's risk of pre-eclampsia, a disorder which occurs in one in every 20 pregnant women. Symptoms of pre-eclampsia are high blood pressure, headache, protein in the urine, blurred vision and anxiety. It can lead to eclampsia, a seizure disorder which can cause complications with pregnancy, and even death. There is some evidence that abnormalities in calcium metabolism are involved in pre-eclampsia. Many pregnant women do not consume enough calcium to ensure optimal blood pressure regulation, and the results of several clinical trials have suggested that calcium supplements reduce the incidence of pre-eclampsia.16

A 1996 analysis of clinical trials which looked at the effects of calcium intake on pre-eclampsia and pregnancy outcomes in 2500 women found that those who consumed 1500 to 2000 mg of calcium supplements per day were 70 per cent less likely to suffer from high blood pressure in pregnancy.17

However, in a study published in 1997 in the New England Journal of Medicine, researchers found that calcium supplements did not prevent pre-eclampsia. The study, the largest ever done on the subject, involved 4589 healthy, first-time mothers. Half of the subjects received 2000 mg of calcium per day and the other half received a placebo. The researchers then assessed the incidence of high blood pressure and protein excretion in the urine. No significant differences in the groups were found. Supplements did not reduce other complications associated with childbirth or increase the incidence of kidney stones.18 The results of this study still leave open the possibility that calcium supplements may be useful as the women included in the study were already consuming higher than average levels of calcium than is typical even before they took the supplements. Women at high risk of pre-eclampsia were also not included in the investigation.

Magnesium

Magnesium deficiency may contribute to high blood pressure. Studies suggest that around 30 per cent of high blood pressure sufferers consume inadequate amounts of magnesium, and high blood pressure is more common in areas where the water is low in magnesium. Magnesium can affect blood pressure by directly exerting effects on blood vessels and by indirectly affecting potassium balance in the body.

Intravenous magnesium has been shown to reduce blood pressure by relaxing constricted blood vessel walls. Changes in magnesium levels may contribute to altered cell membrane calcium binding seen in essential hypertension.

The Honolulu Heart Study, which looked at the relationship between dietary magnesium intake and blood pressure, found that those in the high intake group had, on average, systolic blood pressures 6.4 mmHg lower and diastolic pressures 3.1 mmHg lower than those in the low intake group.19 In another survey of over 58,000 women, researchers found that those with magnesium intakes of less than 200 mg per day had a significantly higher risk of developing high blood pressure than women whose intakes were over 300 mg per day.20 In a study published in 1992, researchers also found that low dietary intakes of magnesium were linked to an increased risk of high blood pressure in over 30,000 men.21

Magnesium supplements may be useful in the treatment of high blood pressure, although the results of studies have been mixed. Intravenous magnesium has been shown to reduce blood pressure, possibly by relaxing constricted blood vessels. Those with high sodium and low potassium levels and those taking diuretic drugs may benefit from magnesium supplements. These drugs can decrease the amount of magnesium in the body as they increase fluid excretion.

In a 1997 double-blind, placebo-controlled study carried out in Japan, 33 people received either a four-week treatment with oral magnesium supplementation (411 to 548 mg per day) or a placebo. The results showed that the systolic and diastolic blood pressure values decreased significantly in the magnesium group, but not in the placebo group. Measurements made during the study suggest that magnesium may lower blood pressure through its effects on the secretion of adrenal hormones and resulting increase in sodium excretion.22

In a 1994 study, 91 middle-aged and elderly women with mild to moderate hypertension who were not on anti-hypertenstive medication were treated with either magnesium supplements or placebo for six months. At the end of the study, both systolic and diastolic pressures had fallen in both groups but the falls in the magnesium group were significantly greater.23

Vitamins and Blood Pressure

Vitamin D

Vitamin D deficiency may play a role in the development of high blood pressure, possibly via effects on calcium metabolism.

Vitamin C

Hypertension sufferers often have low blood levels of vitamin C and increasing intake may help to lower blood pressure. In a study done in Cambridge, UK researchers examined the relationship between blood pressure and vitamin C levels in the blood in 835 men and 1025 women aged from 45 to75. The results showed that low vitamin C levels were associated with higher systolic and diastolic blood pressures.24

Some research suggests that vitamin C supplements may have beneficial effects in lowering high blood pressure.25 They have been shown to improve abnormal artery lining function in hypertensive people.26 Vitamin C supplements may be useful in combination with other treatments.

Other Nutrients

Omega-3 fatty acid supplements may be effective in treating mild hypertension. In a 1996 study of 78 patients with untreated mild hypertension, Norwegian researchers found that overall blood pressure was reduced by about six points in people who took fish oil supplements, compared with those who took a corn-oil placebo.27 In some cases, it may also be an effective addition to drug treatment.28 In a 1996 study, 21 men whose blood pressure was not successfully controlled with anti-hypertenstive medications were randomized to receive either fish oil (4.5 g omega-3 fatty acids per day) or a placebo. Blood pressure readings were taken at the start of the study and at four and eight weeks. Both systolic and diastolic blood pressures were significantly reduced in the fish oil group at both week four and at week eight.29 Supplements have also been useful in preventing high blood pressure in heart transplant patients. 30 However, not all studies have shown beneficial effects. 31

Herbal Medicine and Hypertension

Herbs used to treat hypertension include hawthorn (Crataegus oxyacantha), linden (Tilia europea), yarrow (Achillea millefolium), garlic (Allium sativum) and wild celery (Apium graveolens).


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