Aldosterone is a steroid hormone that raises blood pressure primarily by telling the kidneys to hold onto sodium and water, expanding the volume of fluid in your bloodstream. Produced in the outer layer of the adrenal glands, it is the final effector of a hormonal chain reaction that keeps blood pressure from dropping too low when you lose fluid or salt. But aldosterone does more than adjust fluid volume: it stiffens arteries, acts on the brain to ramp up sympathetic nerve firing, and directly damages the heart when levels stay elevated for too long.
How Aldosterone Controls Sodium and Water in the Kidneys
The kidney is where aldosterone does most of its day-to-day work. In the far end of the kidney’s filtering tubes, aldosterone binds to a receptor inside cells and switches on production of a sodium channel called ENaC, which sits on the inner surface of those tubule cells facing the urine side. When more ENaC channels appear and open, more sodium gets pulled back out of the urine and into the bloodstream. Water follows sodium passively, so the net effect is a larger circulating blood volume and, consequently, higher blood pressure.1PubMed Central. The role of the ENaC-regulatory complex in aldosterone-mediated sodium transport At the same time, potassium ions move in the opposite direction, getting secreted into the urine. This trade is why aldosterone problems almost always involve both blood pressure changes and potassium imbalances.
When aldosterone is absent or the machinery that makes it is broken, the consequences mirror the mechanism in reverse. Inherited defects in aldosterone production cause low blood volume, low sodium, and dangerously high potassium, a combination that can be life-threatening in newborns if not caught quickly.2PubMed. Aldosterone synthase deficiency and related disorders
What Triggers Aldosterone Release
Aldosterone production is tightly controlled by several overlapping signals, but the dominant one is a hormonal cascade known as the renin-angiotensin system. When blood pressure drops or kidney blood flow falls, the kidneys release an enzyme called renin. Renin kicks off a chain of protein cleavages that eventually produces angiotensin II, a powerful vasoconstrictor that also happens to be the most important physiological driver of aldosterone secretion from the adrenal glands.3The Journal of Steroid Biochemistry and Molecular Biology. Factors controlling steroid biosynthesis in the zona glomerulosa of the adrenal Angiotensin II squeezes blood vessels to raise pressure immediately, and aldosterone sustains that pressure over hours by retaining salt and water.
Potassium is the second major trigger. Even a small rise in blood potassium directly stimulates the adrenal glands to pump out more aldosterone, independently of renin. Classic infusion experiments showed that giving potassium intravenously boosts aldosterone without increasing renin activity or ACTH levels.4PubMed Central. Studies of the control of plasma aldosterone concentration in normal man. II. Effect of dietary potassium and acute potassium infusion This makes physiological sense: aldosterone pushes potassium out through the kidneys, so potassium itself acts as a direct feedback signal. ACTH, the pituitary hormone best known for driving cortisol, also nudges aldosterone release, though it plays a smaller day-to-day role than angiotensin II or potassium.5PubMed. Regulation of aldosterone synthesis and secretion
Beyond the Kidneys: What Aldosterone Does to Blood Vessels
If aldosterone only adjusted fluid volume, its story would be straightforward. But research over the past two decades has revealed that it acts directly on blood vessel walls, with consequences that go beyond how much fluid is in the pipes. Aldosterone makes arteries stiffer. In animal studies, aldosterone infusion increased the ratio of stiff structural proteins to elastic ones in the walls of small resistance arteries, the vessels that fine-tune blood pressure moment to moment. That stiffening happened even in mice that lacked the inflammatory immune cells usually blamed for vascular damage, suggesting it is partly a direct structural effect.6Journal of Hypertension. Aldosterone induces arterial stiffness in absence of oxidative stress and endothelial dysfunction
The endothelium, the thin lining of every blood vessel, also responds to aldosterone. The same ENaC sodium channel that aldosterone activates in the kidney exists on endothelial cells. When aldosterone turns on this channel in the vessel lining, endothelial cells swell slightly, become stiffer, and lose some of their ability to relax. In mice engineered to lack the endothelial version of ENaC, the usual aldosterone-driven stiffening and inflammation in the aorta were blunted.7PubMed Central. Epithelial Sodium Channel in Aldosterone-Induced Endothelium Stiffness and Aortic Dysfunction Arterial stiffness matters because it is independently linked to heart attacks and strokes. A stiff artery transmits each heartbeat as a harder pulse wave, forcing the heart to work against greater resistance and battering the small vessels in the brain and kidneys.
Direct Damage to the Heart
Aldosterone also acts on the heart itself, and this effect appears to be partly independent of what it does to blood pressure. Chronically elevated aldosterone activates mineralocorticoid receptors in cardiac tissue, promoting the buildup of collagen (fibrosis) and enlargement of heart muscle cells (hypertrophy). Fibrotic hearts conduct electrical signals erratically and pump less efficiently. Studies using mice lacking a signaling protein called cardiotrophin-1 found that these animals were protected from aldosterone-driven heart enlargement and fibrosis even though their blood pressure stayed the same as that of normal mice receiving aldosterone.8PubMed. A role for cardiotrophin-1 in myocardial remodeling induced by aldosterone Reviews of this evidence broadly support the idea that cardiac mineralocorticoid receptor activation causes tissue damage through pathways that do not depend solely on pressure overload.9PubMed Central. Aldosterone Effect on Cardiac Structure and Function
This is clinically relevant because it means simply lowering blood pressure with a standard drug may not undo all the cardiac harm caused by excess aldosterone. Blocking the mineralocorticoid receptor specifically, rather than just reducing pressure, appears to matter for protecting the heart.
Aldosterone and the Brain
The brain has its own mineralocorticoid receptors, and aldosterone activates them to increase sympathetic nervous system output, the “fight or flight” wiring that raises heart rate, constricts blood vessels, and elevates blood pressure. When researchers infused aldosterone directly into the brains of rats, norepinephrine levels rose and blood pressure crept up. Blocking the brain’s mineralocorticoid receptors, or scavenging the oxidative stress aldosterone generated in the brain, reversed these effects.10PubMed. Aldosterone acts centrally to increase brain renin-angiotensin system activity and oxidative stress in normal rats So aldosterone raises blood pressure through at least three parallel routes: sodium retention in the kidneys, stiffening of arteries, and cranking up sympathetic nerve traffic from the brain. These layers help explain why conditions with high aldosterone can be so difficult to treat with a single drug.
When Too Much Aldosterone Becomes a Disease
Primary aldosteronism is a condition in which the adrenal glands overproduce aldosterone regardless of the body’s actual need. It is now recognized as one of the most common causes of secondary hypertension, estimated to affect roughly 5 to 10 percent of people with high blood pressure and a higher share of those with resistant hypertension. The excess is usually caused by a small benign tumor in one adrenal gland (an aldosterone-producing adenoma) or by overgrowth of both glands’ outer layers (bilateral adrenal hyperplasia). In about 40 percent of adenomas, somatic mutations in a gene called KCNJ5 are responsible, with mutations in other ion-channel and pump genes accounting for additional cases.11PubMed. Somatic ATP1A1, ATP2B3, and KCNJ5 mutations in aldosterone-producing adenomas
What makes primary aldosteronism alarming is that the cardiovascular damage it causes is worse than what you would expect from the blood pressure numbers alone. A systematic review and meta-analysis comparing primary aldosteronism patients with people who had similar blood pressure from ordinary hypertension found that the aldosterone-excess group had roughly double the risk of stroke, nearly quadruple the odds of atrial fibrillation, and about double the odds of heart failure.12PubMed. Cardiovascular events and target organ damage in primary aldosteronism compared with essential hypertension: a systematic review and meta-analysis A separate meta-analysis confirmed elevated risks for stroke and coronary artery disease and added that left ventricular hypertrophy was about 50 percent more common in these patients.13PubMed Central. Cardiovascular risk in primary aldosteronism A systematic review and meta-analysis Cross-sectional data echoed the pattern, finding roughly two and a half times the odds of nonfatal heart attack and five times the odds of atrial fibrillation compared with blood-pressure-matched controls.14PubMed. Cardiovascular complications associated with primary aldosteronism: a controlled cross-sectional study
This disproportionate damage is why early detection matters. The standard screening test uses the ratio of aldosterone to renin in the blood. A meta-analysis of that ratio’s diagnostic accuracy found sensitivity around 89 percent and specificity around 96 percent overall, with even better performance when patients stopped certain blood-pressure medications beforehand.15PubMed Central. Aldosterone/direct renin concentration ratio as a screening test for primary aldosteronism: A meta-analysis Secondary hyperaldosteronism, in which both aldosterone and renin are high, is a different situation: it typically results from something reducing blood flow to the kidneys (like renal artery narrowing), triggering the entire renin-angiotensin cascade. Both forms present with hard-to-control blood pressure, low potassium, and metabolic alkalosis.
Aldosterone’s Effect on Nighttime Blood Pressure
In healthy people, blood pressure dips by about 10 to 20 percent during sleep, a pattern called “dipping.” This nocturnal dip matters because its absence is an independent risk factor for heart attacks and strokes. People with primary aldosteronism frequently lose this dip. A study of these patients found that higher plasma aldosterone and a higher aldosterone-to-renin ratio were both associated with smaller nighttime drops in systolic blood pressure. In patients whose aldosterone levels returned to normal after targeted treatment, the average nighttime systolic pressure fell dramatically, and the proportion of patients with a normal dipping pattern nearly tripled.16PubMed Central. Aldosterone and Impaired Nocturnal Blood Pressure Decline in Primary Aldosteronism Separate work confirmed that primary aldosteronism patients have higher nighttime blood pressure and more cardiac strain markers than people with ordinary hypertension, and that the elevated nighttime systolic pressure is closely linked to cardiac damage.17PubMed. Diurnal blood pressure pattern and cardiac damage in hypertensive patients with primary aldosteronism
The practical takeaway is that 24-hour blood pressure monitoring can be an important clue. If someone’s blood pressure stays stubbornly elevated overnight, that non-dipping pattern should raise suspicion of aldosterone excess, especially if potassium levels are also low.
Why the Body Doesn’t Just Swell Up Forever
If aldosterone tells the kidneys to retain sodium and water, you might expect someone with chronically high aldosterone to accumulate fluid indefinitely. That does not happen, thanks to a phenomenon called aldosterone escape. After a period of sodium and water retention, the rising blood volume itself triggers counter-regulatory forces. Higher pressure at the kidney’s filtering units physically pushes more sodium out, while a hormone called atrial natriuretic peptide, released by stretched heart chambers, directly inhibits sodium reabsorption and increases the filtration rate. Additional local signals in the kidney fine-tune transporter activity to restore some balance.18PubMed Central. The Story of Aldosterone Escape
Aldosterone escape explains why primary aldosteronism patients develop high blood pressure and low potassium but generally do not develop massive fluid overload or severe edema. The kidneys find a new equilibrium, but it comes at the cost of sustained higher pressure, because that extra pressure is itself one of the forces driving the escape. So the body “escapes” the sodium retention but gets stuck with the hypertension.
Blocking Aldosterone With Drugs
The oldest approach to countering aldosterone is to block its receptor. Spironolactone, available since the 1960s, and eplerenone, a newer and more selective alternative, both block the mineralocorticoid receptor. They are used for heart failure, resistant hypertension, and primary aldosteronism when surgery is not an option. A systematic review comparing the two found no significant difference in how much they lowered systolic or diastolic blood pressure in patients with resistant hypertension.19Journal of Asian Pacific Society of Cardiology. Spironolactone versus Eplerenone in Patients with Resistant Hypertension: A Systematic Review and Indirect Meta-analysis The main practical difference is side effects: spironolactone can cause breast tenderness and menstrual irregularities because it also binds to androgen and progesterone receptors, while eplerenone is more selective and generally avoids those problems.
A fundamentally different strategy is to stop the adrenal glands from making aldosterone in the first place. Baxdrostat is a drug that inhibits aldosterone synthase, the enzyme at the very end of the production pathway. In a phase 2 trial of patients with treatment-resistant hypertension, the highest dose of baxdrostat lowered systolic blood pressure by about 11 mm Hg more than placebo, a clinically meaningful reduction in a population that had already failed multiple standard medications.20PubMed. Phase 2 Trial of Baxdrostat for Treatment-Resistant Hypertension The response was dose-dependent, with lower doses producing smaller but still significant reductions. If later trials confirm these results, aldosterone synthase inhibitors could offer a new tool for people whose blood pressure remains dangerously high despite multiple drugs.
Licorice and Look-Alike Syndromes
You can develop symptoms that look exactly like aldosterone excess without aldosterone being elevated at all. The key is a protective enzyme in the kidney called 11-beta-hydroxysteroid dehydrogenase type 2, which normally converts cortisol into an inactive form before it can activate the mineralocorticoid receptor. Cortisol circulates at concentrations far higher than aldosterone, so without this enzyme standing guard, cortisol floods the receptor and mimics aldosterone’s effects. Genetic defects in this enzyme cause a rare condition called apparent mineralocorticoid excess, with severe hypertension, low potassium, and metabolic alkalosis from childhood.21PubMed Central. Glycyrrhizic acid induced acquired apparent mineralocorticoid excess syndrome with a hyperadrenergic state: a case report
You can also acquire the same syndrome by eating large quantities of real licorice. The active compound in licorice root, glycyrrhizic acid, inhibits the same protective enzyme. Case reports describe patients developing severe hypertension and dangerously low potassium from habitual licorice consumption. The lesson is that the mineralocorticoid receptor does not care what activates it. Whether the stimulus is aldosterone, cortisol let loose by a missing enzyme, or cortisol enabled by a licorice habit, the downstream consequences for blood pressure and potassium are the same.
An Evolutionary Perspective on Aldosterone
Aldosterone is not ancient by hormonal standards. It first appears in lungfish, the lobe-finned fish that are considered forerunners of land-dwelling vertebrates.22PubMed. Evolution of the Mineralocorticoid Receptor The gene encoding aldosterone synthase arose through a gene duplication event in the lobe-finned fish lineage after it split from ray-finned fish roughly 420 million years ago, but before vertebrates colonized land around 370 million years ago. Because lungfish are fully aquatic yet already produce aldosterone, researchers have proposed that its original role was not to prevent dehydration on land but rather to help manage the stress of low-oxygen environments.23PubMed. Aldosterone and the conquest of land Only later, as vertebrates moved onto land and faced the constant threat of drying out, did aldosterone’s sodium-retaining abilities become central to survival. The receptor aldosterone binds to, the mineralocorticoid receptor, is far older than aldosterone itself and originally responded to cortisol. As the receptor and its closest relative (the glucocorticoid receptor) diverged over evolutionary time, aldosterone emerged as a dedicated ligand with increasingly specific control over salt and water balance in terrestrial animals.