Medical science doesn't understand what causes most cases of high blood pressure, so it's hard to say how to prevent it. Several factors may contribute to it.

Risk Factors That Can't Be Controlled

• Heredity. People whose parents or other close blood relatives have high blood pressure are more likely to develop it themselves.
  
  
• Race. African Americans are more likely to have high blood pressure than Caucasians, and it tends to occur earlier and be more severe.
  
  
• Increasing age. Blood pressure tends to increase with age, and occurs most often in people older than age 35. Men have a greater risk of high blood pressure than women until age 45. From age 45–54, the percentages of men and women are similar. After age 55, women are more likely to develop high blood pressure than men are.
  

Controllable Risk Factors

• Sedentary or inactive lifestyle. Try to get at least 30 minutes of moderate to vigorous physical activity on most days.
  
  
• Heavy alcohol consumption. Heavy and regular use of alcohol can increase blood pressure dramatically.
  
  
• Sodium (salt) sensitivity.
  
  
• Obesity and overweight.
  
  
• Stress
  

How do salt and sodium affect high blood pressure?

Most Americans consume far more salt (sodium) than their bodies need. Heavy sodium consumption increases blood pressure in some people, leading to high blood pressure. People diagnosed with high blood pressure are often put on sodium-restricted diets.

How does being overweight affect high blood pressure?

Studies have shown that changes in body weight over time and skinfold thickness are related to changes in blood pressure levels. These factors have been linked to the later rise and development of high blood pressure. People who are overweight are more likely to have high-normal to mild high blood pressure.

How does pregnancy affect high blood pressure?

Doctors usually keep a close watch on a woman's blood pressure during pregnancy. Some women who've never had high blood pressure develop it during pregnancy, especially in the last three months. Others who already have the condition see it worsen during pregnancy. Both mother and baby may be in danger if it's not treated.

How do oral contraceptives affect high blood pressure?

A woman taking oral contraceptives is more likely to develop high blood pressure if she's overweight, has had high blood pressure during pregnancy, has a family history of high blood pressure or has mild kidney disease.

How do other medications affect high blood pressure?

Some medications can raise blood pressure and/or interfere with the effectiveness of antihypertensive drugs. People with high blood pressure should tell their doctor all of the prescribed and over-the-counter medicines they're taking, such as these:

• steroids
• nonsteroidal anti-inflammatory drugs (NSAIDs), such as ibuprofen
• nasal decongestants and other cold remedies
• diet pills
• cyclosporine (si"klo-SPOR'in)
• erythropoietin (eh-rith"ro-POI'eh-tin)
• tricyclic antidepressants (tri-SIK'lik an"tih-de-PRES'sants)
• monoamine oxidase inhibitors (mon"o-AM'een OKS'ih-das in-HIB'ih-torz)
• oral contraceptives

Related AHA publications:

• Heart and Stroke Facts
• Understanding and Controlling Your High Blood Pressure (also in Spanish)
• Shaking Your Salt Habit 
• High Blood Pressure in African Americans 
• High Blood Pressure and Stroke 
• "What Is High Blood Pressure?" and "How Can I Reduce High Blood Pressure?" in Answers By Heart kit (also in Spanish kit)
• "Why Should I Limit Sodium?" and "What About African Americans and High Blood Pressure?" in Answers By Heart kit

Related AHA Scientific Statements:
Hypertension