What causes hypertension?
In most cases, the cause of hypertension is unknown, or idiopathic. This form of high blood pressure is called essential or primary hypertension and includes 95% of the American adults with high blood pressure. According to the Centers for Disease Control and Prevention, women are as likely as men to develop high blood pressure; however, for people under 45, it affects more men than women; for people over 65, the number of women increases. Americans of African descent develop high blood pressure more often and at an earlier age than those of European and Hispanic descent.
As people age, high BP is very common. Ninety percent of people with normal BP at age 55 are at risk for hypertension as they age. The diastolic pressure tends to level out and hypertension that involves primarily the systolic pressure (called isolated systolic hypertension) becomes more common. In persons older than 50 years, systolic blood pressure greater than 140 mm Hg is a much more important cardiovascular disease (CVD) risk factor than diastolic blood pressure.
Although it may not be possible to identify the cause of hypertension, several factors are known to increase the risk and to exacerbate it when present. These include:
- Sedentary lifestyle
- Excessive use of alcohol
- Excessive dietary sodium
- Use of oral contraceptives
- Use of drugs such as steroids, cocaine, and amphetamines
- Family history
Hypertension that is due to one or more identifiable underlying conditions is called secondary hypertension and accounts for 5% of those who have high blood pressure. It is important to identify the underlying conditions since treatment of the underlying condition may result in a person's blood pressure returning to normal or near normal levels. Some conditions that result in secondary hypertension include:
- Kidney disease or damage – decreases the removal of salts and fluids from the body, increasing blood volume and pressure. Since hypertension can also cause kidney damage, this can be a progressive problem if left untreated.
- Heart disease – this may affect the force and rate of the heart's contraction. This can also be progressive.
- Diabetes – this condition can damage the kidneys and affect the integrity of the blood vessels over time.
- Arteriosclerosis – a hardening of the arteries that limits their ability to dilate and constrict
- Cushing's syndrome – a disorder that involves increased production of the hormone cortisol by the adrenal gland
- Hyperaldosteronism (Conn's syndrome) – a condition characterized by an overproduction of aldosterone, a hormone that helps regulate the retention and excretion of sodium by the kidneys; it may be due to an adrenal gland tumor (usually benign)
- Pheochromocytoma – a tumor of the adrenal gland (rare and usually benign) that produces excessive amounts of epinephrine, a hormone that the body uses to help it respond to stress; affected people often have severe episodes of hypertension
- Thyroid disease – both excessive and deficient amounts of thyroid hormone production can cause increases in blood pressure
- Pregnancy – hypertension may develop at any time during a woman's pregnancy but is most common during the last trimester, when it can cause preeclampsia (toxemia), a condition characterized by increased blood pressure and retention of fluids.