The causes and risk factors that lead to high blood pressure are explained herein. But before reading further, know what is normal blood pressure so as to get an idea of the basic knowledge of this subject, wherein the normal levels of blood pressure are explained.

High blood pressure or hypertension as it is called by the medical fraternity, is something you do not want to have because its effects can be very dangerous. Knowing each cause of high blood pressure, therefore, becomes important so that you can identify and avoid the risk factors.

What is high blood pressure or hypertension?

High blood pressure is diagnosed when the blood pressure is above the normal limits. It is the force exerted by the blood on the walls of the arteries. Blood pressure is measured when the heart contracts and again when it relaxes.

The pressure of the blood during the contraction of the heart (during systole) is called the systolic blood pressure and the pressure when the heart relaxes (during diastole) is called the diastolic blood pressure.

Blood pressure chart

The chart below shows the normal, prehypertensive, and hypertensive readings:

 Status Systolic blood pressure Diastolic blood pressure
(mm of Hg) (mm of Hg)
Normal 100 to 120 60 to 80-
Prehypertensive 120 to 140 80 to 90
Hypertensive (stage 1) 140 to 160 90 to 100
Hypertensive (stage 2) More than 160 More than 100

Classification of hypertension

There are two types of hypertension:

1) Primary or Essential hypertension: This is found in more than 95% of hypertensive cases and wherein the cause is unknown. It tends to develop gradually over the years.

2) Secondary hypertension: This type of hypertension is found in 5% of cases and it is due to various health conditions such as a kidney pathology or a tumor of the adrenal glands.

There are cases where blood pressure may rise to above 200 mm hg during exercise only. This is called exercise hypertension and such people are potential candidates for secondary hypertension.

Causes and risk factors of essential hypertension

Causes of essential hypertension are not known, but there is found to be an association of certain predisposing risk factors.

  • Age and high blood pressure. At an advanced age, you become more prone.
  • Salt intake and high blood pressure. A normal salt intake of 3.8 gms daily is recommended for individuals of age between 20 to 50 yrs. Some of the people with essential hypertension have been found to take a higher salt intake of more than 5 gms daily.
  • Hereditary predisposition to high blood pressure is an important factor and is seen in about 30 %  of the cases. An individual with either one or both parents of hypertension carries twice the risk of developing essential hypertension.
  • Smoking. Smoking causes an acute increase in blood pressure and heart rate. Nicotine in cigarette smoke acts as an adrenergic agonist, causing local and systemic catecholamine release and also the release of vasopressin. Among other things, vasopressin causes vasoconstriction, which causes the blood pressure to rise.
  • High alcohol intake. Drinking too much alcohol can raise blood pressure to high levels that can impact your health. Having more than three drinks in one sitting temporarily raises your blood pressure, but repeated alcohol abuse can lead to long-term hypertension.
  • Long-standing diabetes is associated with high blood pressure. Diabetes and high cholesterol are strongly associated. High cholesterol in the blood can cause deposits of plaques on the internal arterial walls and make them undergo hardening, called atherosclerosis. That can cause high blood pressure,
  • Certain medicines: Long-term consumption of medications like steroids, birth control pills, SSNRIs prescribed for depression, NSAIDs, recreational drugs like cocaine can cause high blood pressure.

Causes of Secondary Hypertension

Secondary hypertension is due to some pathology and is found in 5% of hypertensive cases.

1. Renal artery stenosis

Renal artery narrowing may be caused by thickening of the arterial wall due to a condition called fibromyalgia or it may result from the increased deposit of cholesterol plaques inside its walls due to increased levels of cholesterol in the blood.

Narrowing of the renal artery causes restricted blood flow to the kidney.  This stimulates the kidney to secrete two hormones called renin and angiotensin. These along with aldosterone from the adrenal gland cause the peripheral arterioles in the body to constrict (narrow) thus increasing the resistance to the blood flow and causing a rise in blood pressure.

2. Adrenal gland tumors

Adrenal gland tumors cause stimulation of the adrenal glands to secrete excessive aldosterone, which causes blood pressure to rise. One of these tumors causes excessive loss of potassium in the urine and this can be diagnosed by decreased levels of potassium in the blood in a hypertensive patient.

Pheochromocytoma is another tumor of the adrenal gland, which causes hypertension by increasing the secretion of catecholamines. This tumor causes recurrent bouts of hypertension along with flushing of the skin, palpitations, and excessive sweating.

These tumors can be diagnosed by blood and urine tests and imaging in cases suspected due to their symptoms mentioned above.

These tumors are removed surgically and most of the time, hypertension corrects itself after the surgery.

3. Coarctation of the aorta

This is a constriction of the aorta occurring usually just above the renal arteries. The aorta is the main blood vessel into which the heart pumps the blood for distribution to all parts of the body. This constriction causes a reduced blood supply to the kidneys and rise in blood pressure as explained aboveTreatment is surgical and occasionally balloon angioplasty may help.

4. Obesity is a major cause of high blood pressure

The relationship between obesity and high blood pressure is well established in children and adults. The mechanism is well explained here. High blood pressure due to obesity is many a time associated with diabetes and increased cholesterol levels.

5. Thyroid problems

Hyperthyroidism (an overactive thyroid) or hypothyroidism (an underactive thyroid) can both cause hypertension.

6. Diabetes

It is not just diabetes but diabetic neuropathy, a complication of diabetes, which can cause high blood pressure. Diabetic neuropathy can damage your kidneys and this can lead to high blood pressure.

7. Polycystic kidneys

Polycystic kidney is a congenital condition (inherited). The kidneys have cysts inside them and cannot function properly. Nonfunctioning kidneys or poorly functioning kidneys cause high blood pressure.

8. Certain medications

Various prescription medicines can cause high blood pressure when taken for prolonged periods. These include:

  • Pain relievers,
  • Antidepressants
  • Drugs used after organ transplants
  • Pain relievers
  • Birth control pills,
  • Decongestants
  • Certain herbal supplements, including ginseng, licorice, and ephedra (ma huang)
  • Cocaine and methamphetamine, also increase blood pressure

9. Smoking

Hazardous chemicals, including nicotine found in cigarette smoke damage the inner lining of the blood vessels and make them lose their elasticity. Loss of elasticity of the peripheral or distal arterioles (small arteries) is another factor as this condition causes resistance to the blood flow and thus increases the pressure of the blood inside the arterioles.