High blood pressure is often called a “silent” condition. New research points to something more unsettling: for a large share of patients, a hidden and often treatable cause of their hypertension may be slipping past standard tests — because it reveals itself mainly at night.
The overlooked culprit
The condition is primary aldosteronism, a hormone disorder in which the adrenal glands (small glands atop the kidneys) overproduce aldosterone, a hormone that regulates salt and water. Excess aldosterone raises blood pressure. Long considered rare, primary aldosteronism is now recognized as the most common cause of secondary hypertension — and this research suggests it may affect up to 1 in 5 people with high blood pressure, potentially millions of undiagnosed patients.
Why standard tests miss it
The key discovery is about timing. Researchers found that in these patients, the adrenal glands release aldosterone in bursts during nighttime sleep, rather than staying consistently elevated. Standard diagnosis relies on a single blood sample, usually taken during the day — often precisely when hormone levels look normal. As the researchers put it, current approaches “may miss some patients because aldosterone does not remain consistently elevated.” Related hormones (18-hydroxycortisol and 18-oxocortisol) showed similarly abnormal patterns.
How they caught it
The team used a wearable device called U-RHYTHM that samples hormone levels every 20 minutes over 24 hours, painting a continuous picture rather than a single snapshot — and revealing the nighttime surges that spot-testing overlooks. The proof-of-concept study followed 60 patients across Bristol, Bergen, Stockholm and Athens, and was published in Science Translational Medicine by researchers from the universities of Bristol, Manchester and Bergen and collaborators.
Why it matters
This is more than an academic curiosity, because primary aldosteronism is potentially curable. In the study, surgically removing an affected adrenal gland resolved the abnormal hormone patterns; in other cases, specific medicines can control it. That means people currently labeled with hard-to-treat “essential” hypertension — and taking multiple pills with limited success — might actually have a specific, fixable problem. Catching it also matters because excess aldosterone independently damages the heart and kidneys beyond its effect on blood pressure.
The caveats
This is an early, small proof-of-concept study, and the U-RHYTHM device is a research tool, not yet routine clinical equipment. Wider validation is needed before nighttime hormone monitoring changes standard practice. But the finding reframes a common problem: some “stubborn” high blood pressure may be a missed diagnosis rather than an untreatable condition. Anyone whose hypertension is difficult to control should discuss possible secondary causes with their doctor. This summarizes research and is not medical advice.