Hypertension is referred to as essential, or primary, when the physician is unable to identify a specific cause. It is by far the most common type of high blood pressure. While the causes of this type are unknown, they are likely to be a complex combination of genetic, environmental, and other factors.
Several genetic factors play a major role in essential hypertension. One system of particular interest involves the genes that regulate a group of hormones known collectively as the angiotensin-renin-aldosterone system. This system plays a role in all aspects of blood pressure control, including how narrow or wide the blood vessels are, and how the body manages salt and water.
Experts believed that this system may have evolved millions of years ago, having the body hold on to salt and water to protect early humans during times of drought or stress. However, as humans have become more accustomed to industrialized living, this primitive system may make certain people more susceptible to developing hypertension.
Inherited abnormalities in the nervous system
Studies suggest that some people with essential hypertension may inherit abnormalities of the sympathetic nervous system. They are therefore more sensitive to the effects of adrenaline. This is the part of the nervous system that controls heart rate, blood pressure, and how narrow or wide the blood vessels are.
High blood pressure is strongly associated with diabetes, both types 1 and 2. For people with type 1 diabetes, kidney damage is generally the cause of high blood pressure.
For people with type 2 diabetes, being overweight or obese is associated with high blood pressure. However, even thin people with type 2 diabetes often have high blood pressure. Scientists believe that the inability of the body to use insulin (called insulin resistance, the cause of type 2 diabetes) may lead to retention of sodium -- a contributor to high blood pressure. Increased amounts of a protein called albumin in the urine is a warning that blood pressure and diabetes is harming the kidney and increasing the risk of other organ damage.
Diabetes in combination with high blood pressure is particularly dangerous. People with these two conditions have a higher risk of developing life-threatening problems such as heart disease, kidney failure, and stroke.
Obesity, on its own, has a number of possible effects that could lead to high blood pressure. For example, being overweight means the heart has to pump more blood to supply the extra tissue in your body. The larger blood volume increases the work of the heart and the pressure on blood vessels. Other factors, such as insulin resistance, abnormal fat regulation, and breathing problems during sleep, may contribute to the long-term risk of high blood pressure. Fat cells also produce hormones that may affect blood pressure. Weight loss alone can lead to marked reductions in blood pressure.
Low levels of nitric oxide
Nitric oxide (a gas) is produced in the body and helps keep muscle cells that line blood vessels relaxed and flexible. It may also help prevent blood from clotting. Low levels of nitric oxide have been measured in some people with high blood pressure (particularly in African-Americans) and may be an important factor in essential hypertension.
Review Date: 6/8/2011
Reviewed By: Larry A. Weinrauch MD, Assistant Professor of Medicine, Harvard Medical School, Cardiovascular Disease and Clinical Outcomes Research, Watertown, MA.. Review provided by VeriMed Healthcare Network. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.