What causes high blood pressure?
The majority of times, there is no clear cause which can be identified. In a few patients (approximately 2%), high blood pressure may be traced to other "secondary causes" (see next section). High blood pressure can have many causes. In younger children, the most common causes are related to kidney problems. Sometimes, it is the finding of the high blood pressure that alerts doctors to discover the kidney problem. In a small percentage of cases they are related a narrowing of the body's largest blood vessel, the aorta and in about 1% of cases, there is a hormonal cause. In at least ½ of he adolescents with high blood pressure we can't find a specific cause and we label it "essential hypertension." Scientists are still working to understand the causes of essential hypertension but we do know that obesity and high salt intakes are associated with hypertension. In 90 percent to 95 percent of the cases, hypertension has no known cause.
This type of high blood pressure is known as essential hypertension. In rarer cases, high blood pressure can result from other illnesses like kidney or adrenal gland problems. That type of high blood pressure is called secondary hypertension. In people over age 65, the incidence of high blood pressure is almost the same among men and women. In this age group, about 63 percent of whites and 76 percent of blacks will develop hypertension.
The actual mechanisms which explain why the blood pressure is high has to do mainly with the constriction of the small arterioles which are in all of the tissues of the body. When these are even slightly smaller than normal, the overall effect is that of a marked decrease in the volume that blood can flow in. High blood pressure is more common in patients whose families have high blood pressure in those over 35 years old, in males, in Afro-Americans, and in women on oral contraceptives. High blood pressure has its roots in many cases simply with the genes we received from our parents. High blood pressure is far more common in families where other members have this condition. This does not mean that you must have a history of high blood pressure in your family to have it yourself. It is very interesting to note that while the incidence of high blood pressure is low in Japan, it is higher in Japanese who migrate to America, underscoring the idea that there are things that we do culturally that will affect the incidence of high blood pressure. These include being overweight, eating high sodium diet, exercising too little, and drinking more than two alcoholic drinks daily.
There are many other factors which have been felt to be related to high blood pressure. While these are interesting topics of debate and scientific curiosity, they are not nearly as important as the factors listed above. The "average" or "run of the mill" case of high blood pressure is caused by the genes that are inherited with very important contributions from lifestyle. This is "Primary" Hypertension, and is discussed in the section above. About 2% of the time, there are specific abnormalities which are an identifiable reason for high blood pressure in some people. Some of these causes include"
Adrenal glands live right above the kidneys, and are responsible for releasing many hormones which regulate blood pressure and other functions. They are composed of an inner and an outer layer. The inner layer produces substances such as "adrenaline" which we've all heard of. The outer layer produce various steroid hormones. Disorders include the next three items. "Pheochromocytoma", a long term for one of the rarest of all human tumors. Since high blood pressure is so common however, doctors think about it way more often then they ever find it. This tumor produces adrenaline and/or similar substances. Patients with this disorder typically have "paroxyms" or spells of high blood pressure which are accompanied by strong and rapid heart beats, sweating and headaches. Cushing's syndrome is caused from the overproduction of "glucocorticoids" -- steroids that participate in regulating the metabolism of glucose and other food substances. The site of this overproduction is in the adrenals, although they may be simply reacting to stimulation by other abnormal organs. Adrenal "adenomas" (non-malignant tumors) or "hyperplasia" (too much tissue growth) can be responsible for excess levels of "mineralcorticoids" -- steroids which participate in the regulation of sodium, potassium, and other minerals. Their effect is primarily from holding onto too much sodium. An obstruction to the arteries to the kidneys ("Renal Artery Stenosis"). In this situation, the kidney which is blocked doesn't "see" enough blood pressure, and releases chemicals causing the blood pressure to go up. In this way, that kidney may produce enough blood pressure to satisfy itself, while the rest of the body sees very high pressures as a result. This obstruction can come from atherosclerosis (blockage with cholesterol) or from a congenital disorder of the connective tissue in the blood vessels (Fibromuscular Dysplasia).
A "Coarctation" (or narrowing) of the aorta can cause high blood pressure in a manner similar to Renal Artery Stenosis noted above. This is a congenital condition present from birth where narrowing occurs in the aorta, typically just beyond the point where the artery to the left arm is given off. Blood has to find a way around the obstruction so that there is enough flow for the abdomen, legs, etc. The body is usually successful at providing enough blood around the obstruction, but the pressure is low, including the pressure to the kidneys. They behave in exactly the same way they do in Renal Artery Stenosis, releasing chemicals to raise their own pressure. However, the pressure in the upper half of the body, particularly the heart and the brain, see very high pressures and can therefore have all of the complications of high blood pressure.
Sleep apnea, a disorder in which breathing halts briefly but repeatedly during sleep, is now highly associated with hypertension. A weak but still higher than normal association with high blood pressure has even been observed in those who snore or have mild sleep apnea. The relationship between sleep apnea and hypertension has been thought to be largely due to obesity, but major studies are finding a higher rate of hypertension in people with sleep apnea regardless of their weight. Treating sleep apnea with a device known as nasal continuous positive airway pressure may have modest benefits blood pressure as well. Their presence may be suggested by an early age of onset of hypertension, or a sudden worsening, or difficulty in treatment. Still, most cases even in these categories will be due to "plain old primary" hypertension. Investigations to "rule out" these conditions may include a careful history, particularly for some of the kidney diseases. Various features of the physical examination, including bruits (particular noises heard with the stethoscope when blood rushes through narrowed arteries) in the case of Renal Artery Stenosis, or substantial differences in the blood pressure in the arms and legs (in the case of coarctation) can be helpful. Measuring certain chemicals in the blood or urine are important in the abnormal conditions of the adrenal gland. Specialized imaging techniques, such as ultrasound, nuclear medicine studies, CT scans or MRI's, or arteriograms may be needed to diagnose the disorders.
Long-term use of nonsteroidal anti-inflammatory drugs (NSAIDs) may injure the kidney and is an important cause of secondary hypertension in the elderly population. Such drugs include aspirin, ibuprofen (Advil, Motrin, Rufen), naproxen (Anaprox, Naprosyn, Aleve), and many others. Of these drugs, aspirin appears to have the least detrimental effect on blood pressure. Cold medicines containing pseudoephedrine have also been found to increase blood pressure in hypertensive people, although they appear to pose no danger for those with normal blood pressure. Oral contraceptives (the Pill) increase the risk for high blood pressure, particularly in women who are older, obese, smokers, or some combination. Stopping the Pill nearly always reduces blood pressure, although a recent study suggests that oral contraceptives may produce a small but significant increase in diastolic pressure that persists in some older women who have been off the Pill for years.
An estimated 10% of hypertension cases are caused by alcohol abuse (ie, three alcoholic drinks a day or more, with heavier drinkers having higher pressure). In one study, binge-drinkers had even higher blood pressure than people who drank regularly. One study found alcohol abuse associated with low diastolic but high systolic pressure. Moderate drinking (one or two drinks a day) has benefits for the heart and may even protect against some types of stroke. Of some concern was a study suggesting the even low or moderate drinking may increase the risk for hypertension in African Americans. Red wine specifically may have chemicals that benefit blood pressure. Smoking is a major risk factor. One study reported that smokers have blood pressures up to 10 points higher than nonsmokers. Caffeine causes a temporary increase in blood pressure, which has been thought to be harmless in people with normal blood pressure. Studies are suggesting, however, that regular, heavy coffee drinking (an average of 5 cups per day) can boost blood pressure, and there is growing evidence that a high intake of coffee may be harmful in people with hypertension and may even increase their risk for stroke. Drinking coffee also increases excretion of calcium, which also may affect blood pressure.