High blood pressure — which has no symptoms or warning signs — can harm your blood vessels, heart, brain, eyes, and kidneys. An estimated 46% of adults in the United States have this stealth condition. A combination of unhealthy habits, such as smoking, a poor diet, and lack of exercise, can contribute to a rise in blood pressure. While kidney disease may cause high blood pressure, for most people the underlying cause is unknown.
However, for about one of every 15 people with high blood pressure, an imbalance of the hormone aldosterone may be to blame. This problem may be even more common among people with poorly controlled high blood pressure (also called resistant hypertension). "Among those people, up to one in five may have too much aldosterone," says Dr. Gail Adler, chief of cardiovascular endocrinology at Harvard-affiliated Brigham and Women's Hospital.
Aldosterone is a key regulator of sodium and potassium in the body, she explains. If you're out in the desert, your body needs aldosterone to retain sodium and water to maintain your blood pressure. But too much aldosterone makes the kidneys retain too much sodium and water, and that extra fluid ends up in the bloodstream, leading to increases in blood pressure, says Dr. Adler.
Causes of excess aldosterone
The triangle-shaped adrenal glands, which perch atop each of the kidneys, produce several key hormones, including aldosterone (see "Anatomy of an adrenal gland"). When these glands produce too much aldosterone, the condition is known as primary aldosteronism. A common cause is a benign (noncancerous) growth in one adrenal gland, known as Conn's syndrome. Some people have idiopathic hyperaldosteronism, an overactivity in both glands with no known cause.
Overactive adrenal glands were once thought to be a relatively rare cause of high blood pressure. "But we're now recognizing that primary aldosteronism may be just the tip of the iceberg," says Dr. Adler. There may be a continuum leading up to the problem, including larger numbers of people with less obvious symptoms.
Beyond blood pressure
A resurgence of interest in aldosterone over the past decade led to the discovery of receptors for aldosterone not just in the kidneys but in blood vessels, white blood cells, fat cells, and heart muscle cells (cardiomyocytes). And there is growing evidence that excess aldosterone may affect the heart in ways other than via high blood pressure.
For example, high aldosterone levels may promote the thickening and scarring of heart muscle tissue, known as cardiac fibrosis. High aldosterone levels also may contribute to coronary microvascular disease, which is characterized by damage to the walls of the small arteries in the heart. This condition, which may be more prevalent in women and people with diabetes, causes symptoms of heart disease such as chest pain, shortness of breath, and fatigue. Recent research by Dr. Adler and colleagues found that spironolactone (Aldactone), an older blood pressure drug that blocks aldosterone, improves blood flow through the heart's arteries in people with diabetes.
In addition, some statins may also lower aldosterone levels. This potential decrease in aldosterone (in addition to statins' cholesterol-lowering effects) may help reduce heart disease, says Dr. Adler.
Who should be tested?
One sign of hyperaldosteronism is low blood potassium levels, which may (but not always) cause symptoms such as weakness, heart rhythm abnormalities, and muscle cramps. People with high blood pressure and low potassium may need a blood test for aldosterone and for renin, a protein made by the kidneys.
An MRI or CT scan of the abdomen can reveal an abnormal growth on an adrenal gland. Blood samples taken from both the right and left adrenal veins can identify which adrenal is making too much aldosterone. Minimally invasive surgery to remove the affected gland often completely corrects both high blood pressure and low potassium.
Overactivity in both glands is usually treated with spironolactone or a related drug, eplerenone (Inspra). Both drugs block aldosterone's action in the kidneys and elsewhere.
(Harvard Heart Letter)
