High blood pressure can be divided into two main types based on its cause: primary hypertension and secondary hypertension.

Causes of Primary Hypertension

Scientists aren’t sure exactly what causes this common form of high blood pressure, which makes up 90 to 95 percent of cases in adults. Primary hypertension isn’t directly attributable to any one underlying condition – it is caused by a combination of factors. However, changes in the arteries over the years are often associated with higher blood pressure. Such changes include:

  • Buildup of fatty deposits inside arteries (atherosclerosis)
  • Thickening of artery walls
  • Excessive contraction of small arteries (arterioles)
Causes of Secondary Hypertension

This form of high blood pressure makes up five to 10 percent of cases in adults as well as most cases in children younger than 10. Secondary hypertension is the direct result of an underlying health condition that causes blood pressure to shoot up. It can have a number of causes.

Kidney disease

Kidney disease is the most common cause of secondary hypertension. The kidneys regulate the amount of fluid in the body. When there is a kidney problem, the volume of blood may increase. The more blood that must be pumped through the arteries, the higher the force that is needed.

High blood pressure can be caused by several forms of kidney disease. Polycystic kidney disease is an inherited condition characterized by cysts in the kidneys. Diabetic nephropathy occurs when diabetes damages the kidneys’ filtering system. Glomerular disease is characterized by swelling of microscopic kidney filters called glomeruli. High blood pressure can also result from a blockage inside the kidneys (hydronephrosis) or narrowing of the arteries leading to them (renovascular hypertension).

Hormonal disorders

The adrenal glands, which sit atop the kidneys, produce hormones that affect blood pressure. In Cushing’s disease, the adrenal glands release too much cortisol, which causes blood pressure to rise. In aldosteronism, they release too much aldosterone, which affects kidney function.

Other glands and their hormones can play a role, too. In hypothyroidism, the thyroid gland produces too little thyroid hormone, which can drive up blood pressure. In hyperthyroidism, the same gland releases too much thyroid hormone. Ironically, that can also raise blood pressure by increasing the activity of two other hormones, epinephrine and norepinephrine. In hyperparathyroidism, the parathyroid glands secrete too much parathyroid hormone, which increases calcium in the blood. That, in turn, can trigger a blood pressure increase.

Heart defect

Some people are born with a narrowed aorta, the largest artery in the body. As a result, the heart has to pump harder to push blood through the aorta. The extra force required raises blood pressure, particularly in the arms. This condition is called “coarctation of the aorta.”

Sleep apnea

Sleep apnea is a disorder characterized by repeated little pauses in breathing during sleep. This reduces the amount of oxygen in the body. Insufficient oxygen may damage the lining of blood vessel walls, making them less effective at regulating blood pressure.

Pregnancy

High blood pressure problems occur in six to eight percent of U.S. pregnancies. Preeclampsia is a potentially serious condition that arises during the second half of pregnancy and is characterized by high blood pressure and excess protein in the urine. Gestational hypertension refers to high blood pressure that starts during pregnancy but isn’t accompanied by excess urinary protein.

Drugs and supplements

Numerous prescription and over-the-counter (OTC) medicines can cause or worsen high blood pressure in certain individuals. These include birth control pills, hormone replacement therapy, cold-relief medicines, OTC and prescription pain relievers, antidepressants, asthma medications, and drugs used for organ transplants. Some herbal supplements, such as ginseng and Saint John’s Wort, also have this effect. In addition, many illicit drugs, such as cocaine and methamphetamine, raise blood pressure.

Obesity

As a general rule of thumb, the more weight on a person’s body, the higher the amount of blood needed. More blood pumping through the body leads to additional pressure on the artery walls, which in turn increases blood pressure. Excess weight can also increase heart rate, which can also raise blood pressure.