Hypertension Causes; What Causes High Blood Pressure?

What Causes High Blood Pressure?

Hypertension is a common disease. The World Health Organization (WHO) reported that hypertension affects 1.13 billion people worldwide, especially in low- and middle-income countries.

If you want to avoid hypertension, you need to know more about the causes and risk factors to be able able to notice the problem early -in case it affects you- and seek early treatment. Keep in mind it is mostly asymptomatic and may progress to dangerous complications without remarkable effects (which is why is named a silent killer).

Hypertension is classified according to its causes into types:

  1. Primary hypertension (Essential hypertension): This type has no apparent causes, but it has a strong association with some risk factors.
    It is the most common and represents 90-95% of hypertensive patients.
  2. Secondary hypertension: This type has specific causes leading to it.
    It is less common and represents 5-10% of hypertensive patients.

First, let’s discuss the risk factors of primary hypertension.

These risk factors are divided into two categories:

A) Non-modifiable risk factors (personal risk factors):

  • Age: The risk of hypertension increases with age as the walls of blood vessels lose their elasticity. It is more common among people over 65 years, and uncommon among patients aged 20 years or less.
  • Gender: Below the age of 50, hypertension affects males more than females, but after 50, it affects females more than males due to the hormonal changes in menopause.
  • Familial history: Hypertension runs in families. Thus, the risk is higher in people from families with a medical history of this disease.
  • Race: The risk of hypertension is higher in black people (e.g. African-American people). They usually develop hypertension at an earlier age and will be more susceptible to its complications than other races.

B) Modifiable risk factors:

  • Smoking: It is a common risk factor that damages the walls of blood vessels and causes hypertension.
    Also, passive smoking (exposure to smokers’ smoke) increases the risk for non-smokers.
  • Obesity and overweight: The risk of hypertension is higher in obese and overweight people.
    Excess weight results in an increased need for oxygen and nutrient supply, which forces the heart to work harder, increases the blood volume in the arteries and increases the pressure on their walls causing hypertension.
    The Framingham Heart Study (robust cardiovascular risk study continued for 44 years) reported that obesity and overweight caused 26% of the hypertension cases in males and 28% in females.
  • Unhealthy diet: An unhealthy diet increases the risk of hypertension, especially salty and fatty diet.
    • Lots of salt (sodium) retains the fluids in your body, which increases the blood volume and causes hypertension.
    • Also, a fatty diet (rich in saturated fatty acids) accumulates cholesterol in your blood vessels and damages their walls. More than 50% of hypertensive patients have high cholesterol in their blood.
    • Also, a diet rich in calories and sugar increases the risk of hypertension.
  • Lack of physical activity: Lack of physical activity in your lifestyle increases the risk of hypertension.
    Inactive people have a high risk of obesity.
    Also, they have an elevated heart rate which forces the heart to work harder and increases the pressure in the arteries causing hypertension.
  • Alcohol: Excessive drinking raises the risk of hypertension because it increases the risk of obesity and overweight as well as the fats in the blood, which damages the walls of blood vessels.
  • Stress: Busy, noisy, sophisticated urban life increases the risk of hypertension due to chronic stress, which raises other risk factors such as alcohol drinking and smoking.
  • Pregnancy: The risk of hypertension is higher in pregnant females than in non-pregnant females.

Second, let’s discuss the causes of secondary hypertension.

Secondary hypertension has certain conditions that lead to it, such as kidney diseases, endocrinal diseases, side effects of some drugs, toxaemia of pregnancy, etc.

1) Kidney diseases

Many renal diseases cause hypertension. For example, inflammatory conditions like glomerulonephritis-pyelonephritis. There are also diabetes complications, as in diabetic nephropathy, congenital diseases like polycystic kidney disease, and vascular diseases such as renal artery stenosis.

These diseases cause hypertension by two mechanisms:

  • They may cause renal failure, which reduces the urine output and leads to sodium and water retention, which causes hypertension.
  • Renal artery stenosis reduces the blood supply to the kidneys and causes renal ischemia, leading to an over-secretion of a renal hormone called renin that stimulates the production of angiotensin II and causes vasoconstriction and hypertension.

2) Adrenal diseases

You have two adrenal glands -above your kidneys- secreting blood pressure-regulating hormones such as catecholamines (adrenaline and noradrenaline), aldosterone, and cortisol.

The following Adrenal diseases can cause hypertension:

  • Hyperaldosteronism (Conn’s syndrome): Over-secretion of aldosterone hormone (salt-retaining hormone) causes salt and water retention which causes hypertension.
  • Pheochromocytoma: An adrenal tumour that secretes large amounts of catecholamines (adrenaline and noradrenaline), which causes vasoconstriction and hypertension.
  • Hypercortisolism (Cushing’s syndrome): Over-secretion of cortisol, which increases blood pressure by promoting rapid weight gain, salt and water retention, and increased levels of stress.

3) Endocrinal conditions

Beside adrenal gland diseases, other endocrinal conditions may cause hypertension, such as:

  • Parathyroid diseases (hyperparathyroidism): Parathyroid glands secrete parathormone hormone (calcium-releasing hormone).
    Parathyroid diseases – that increase parathormone- raise calcium levels in the blood which causes hypertension.
  • Thyroid diseases (hyperthyroidism or hypothyroidism):
    Hypothyroidism increases the cholesterol levels in the blood, and this damages your arteries and reduces the elasticity of their walls causing hypertension.
    Hyperthyroidism forces your heart to work harder and raises blood pressure. It also stimulates other causes of hypertension such as catecholamines secretion.
  • Pituitary diseases: pituitary tumours may increase the secretion of adreno-cortico-trophic hormone (ACTH). This raises the secretion of cortisol and ultimately causes hypertension.

4) Diabetes

Diabetes causes hypertension by several mechanisms:

  • Diabetes damages the walls of blood vessels, causing atherosclerosis and hypertension.
  • It damages the kidney, which plays an essential role in blood pressure regulation, causing hypertension.
  • Diabetic patients have a high risk of obesity and overweight, which increases the risk of hypertension.

5) Toxaemia of pregnancy

This condition causes vasoconstriction either directly or by secretion of a substance called pressor polypeptide -coming from the placenta- which causes hypertension.

6) Polycythemia

It increases the blood viscosity -due to the increasing number of blood cells- which raises blood pressure readings.

7) Some drugs

Hypertension may happen as a side effect of some drugs such as contraceptive pills, non-steroidal anti-inflammatory drugs (e.g. aspirin-ibuprofen-diclofenac), and corticosteroids (e.g. prednisone).