Hypertension affects an estimated 29 percent of adults in the United States. Prevalence of the condition increases with age, and approximately 63 percent of people over age 60 are affected. In African Americans, the condition is more common, starts at a younger age, and is more severe than in other populations.

Hypertension can have a variety of causes. Secondary hypertension results from other disorders that raise blood pressure in addition to other problems. Rare, genetic forms of hypertension are caused by mutations in particular genes, many of which help control the balance of fluids and salts in the body and affect blood pressure. The causes of essential hypertension, however, are not well understood. Essential hypertension is a complex condition with a variety of factors, both genetic and environmental, contributing to its development.

More than 100 genetic variations have been associated with essential hypertension. While these variations have been found more commonly in people with essential hypertension than in unaffected individuals, none are common causes of the condition.

The most-studied genetic association in essential hypertension is with genes involved in the renin-angiotensin-aldosterone system. The renin-angiotensin-aldosterone system is a step-wise process that produces hormones to regulate blood pressure and the balance of fluids and salts in the body. Because these genes play an integral role in normal blood pressure control, researchers suspect that variations in them might impair blood pressure control and contribute to hypertension.

Other genes associated with essential hypertension are important for the normal function of the lining of blood vessels (the vascular endothelium). Changes in these genes are thought to impair this cell layer (endothelial dysfunction). Such changes may result in vessels that are abnormally constricted or narrowed, which raises blood pressure. Still other genes have been linked to hypertension risk, although the roles most of them play in development of the condition are still unclear.

Environmental factors also contribute to hypertension. In addition to race and age, activity level, alcohol consumption, and salt intake influence blood pressure. Other disorders, such as obesity, diabetes, and obstructive sleep apnea also increase the risk of developing hypertension.

Researchers suspect epigenetic changes to the DNA also play a role in development of essential hypertension. Epigenetic changes modify DNA without changing the DNA sequence. They can affect gene activity and the production of proteins, which may influence blood pressure.