How Does High Blood Pressure Hurt the Kidneys?

Chronic uncontrolled high blood pressure damages and weakens blood vessels throughout the body (National Institute of Diabetes and Digestive and Kidney Diseases [NIDDK]). Small capillaries in the kidneys are especially vulnerable. As damage to these capillaries worsens, kidneys lose their ability to function properly, and eventually kidney failure develops. Kidney damage is undetectable until it is in late stages.

What is High Blood Pressure

• Blood pressure is the force by which the blood is pumped through the arteries. A blood pressure reading measures the force of the blood while the heart is pumping (systolic pressure, the first number) and while the heart is at rest between beats (the diastolic pressure, the second number). High blood pressure, or hypertension, results from blood moving at increased pressure through narrowed arteries (such as from plaque buildup) or arteries that have hardened or stiffened walls (NIDDK). Hypertension may also be caused by a higher-than-normal volume of blood moving through healthy arteries. A normal blood pressure is 120/80 mmHg or below.

Hypertension and Kidney Damage

• Uncontrolled hypertension damages blood vessels all over the body, including the heart and kidneys (NIDDK). High blood pressure forces the heart to pump harder to circulate blood and provide enough oxygen to organs and tissues. Long-term pressure weakens and damages blood vessels, particularly the smaller capillaries in the kidney nephrons (American Kidney Fund [AKF]). Nephrons filter out waste in the blood and maintain fluid volume. Chronic high blood pressure permanently damages the nephron capillaries and prevents the kidneys from working properly. The damage worsens as long as blood pressure remains elevated. As continued hypertension increases the damage to kidneys, the ability of the kidneys to filter blood diminishes. The kidneys also lose the ability to maintain proper blood volume, thus further increasing blood pressure in a negative spiral. Kidney damage is always associated with high blood pressure (American Association of Kidney Patients [AAKP]).

Risk Factors

• Hypertension causes one quarter of all kidney failures (AKF), and it worsens and accelerates kidney damage regardless of other factors such as age, race or cause of kidney disease (AAKP). Although every person with high blood pressure is at risk for kidney damage, certain factors increase the chances of developing kidney failure. African-Americans are a higher risk for both hypertension and hypertension-related kidney damage than Caucasians, even when blood pressure is only slightly higher than normal (NIDDK). People with diabetes are also at higher risk for hypertension-related kidney damage.

Prevention

• Controlling hypertension slows the progression of kidney disease (AAKP). Kidney damage does not become apparent until it is advanced, so it is important for people with hypertension to have regular check ups and to follow all instructions for lowering and maintaining a healthy blood pressure. Lifestyle changes that help maintain a healthy blood pressure include weight loss; a healthy diet consisting of fresh fruits, vegetables and low-fat dairy products; limited sodium and alcohol intake; and regular exercise.

Hypertension Medications

• A number of medications effectively manage blood pressure, including diuretics, angiotensin-converting enzyme (ACE) inhibitors, angiotensin receptor blockers (ARBs), beta-blockers and calcium-channel blockers. Of these, ACE inhibitors and ARBs slow the progression of kidney damage while lowering blood pressure. Among African-Americans, ACE inhibitors are more effective in slowing kidney damage than ARBs, but ACE inhibitors do not control blood pressure as well as other medications.