High blood pressure is a condition wherein the force of blood pushing against the wall of your artery is consistently too high. There are various causes of high blood pressure which includes sedentary lifestyle, stress, poor sleep and others. A new study has found another possible reason that can lead to high blood pressure. This can also explain why some cases of high blood pressure can remain hidden despite routine testing. Researchers found that primary aldosteronism, a hormone-related condition, may cause bursts of the hormone aldosterone at specific times, particularly during sleep. Since usual blood tests only measure hormone levels at one point in time, they may miss these temporary surges.

The study, published in Science Translational Medicine, used a wearable monitoring system to track hormone levels continuously over 24 hours, giving researchers a better picture of what happens inside the body during the day and night. Primary aldosteronism is significant because it is a potentially treatable cause of high blood pressure and it may also affect up to one in five people with hypertension. The condition can also make the kidneys retain sodium and water, which increases blood pressure levels. And, high blood pressure increases the risks of several health conditions, including heart disease, stroke and diabetes.

What Is Primary Aldosteronism?

Primary aldosteronism occurs when the adrenal glands produce too much aldosterone. These small glands sit above the kidneys and produce several hormones that help regulate important body functions. Aldosterone plays a key role in controlling sodium, potassium and fluid levels. When too much of it is produced, the kidneys hold on to more sodium and water. This increases the amount of fluid circulating in the bloodstream and can increase blood pressure levels.

Why Routine Tests May Miss It

Doctors can test for primary aldosteronism by checking hormone levels in the blood. However, the new research suggests that the hormone may not stay continuously elevated in people with the condition. Instead, the hormone can be released in repeated bursts, including during the night. A blood sample collected during a period when aldosterone happens to be relatively low may therefore appear normal, even though the person has the disorder.

Researchers found that in some people, hormone levels dropped below the usual thresholds used for diagnosis despite the presence of primary aldosteronism. This explains why the condition is frequently missed or diagnosed late.

What Did The New Study Find?

The study involved 60 patients in Bristol, Bergen, Stockholm and Athens. Researchers monitored their hormone levels continuously over a 24-hour period. They used a lightweight wearable device called U-RHYTHM, which was attached around the waist. The system collected samples from the skin and measured hormone levels every 20 minutes, allowing participants to continue their normal activities, including sleeping at home.

The researchers tracked aldosterone as well as two related hormones, 18-hydroxycortisol and 18-oxocortisol. The data showed previously hidden nighttime bursts of hormone production in people with primary aldosteronism. These unusual patterns were particularly noticeable in people whose condition was linked to one adrenal gland.

Dr Thomas Upton, Clinical Research Fellow in Automated Sampling Clinical Fellow at the University of Bristol, and Senior Clinical Fellow at Bristol Hospitals NHS Foundation Trust, and co-lead author of the study said, "Primary aldosteronism is an important cause of high blood pressure and the most common cause of secondary hypertension we see in our blood pressure clinic. It could be affecting millions of people in the UK. However, due to the way hormones change during the day and the current complexity of the diagnostic process, diagnosis is often delayed or never made at all.

"In our study, patients were monitored at home during normal activity, and this allowed us to see how hormones changed over time in realistic settings. This approach could potentially revolutionize how we diagnose hypertension and ultimately reduce cardiovascular disease - particularly heart disease and strokes - that could have been prevented."

Could Hormone Monitoring Change Diagnosis?

Researchers say the findings could eventually lead to a shift from single-time-point blood tests towards monitoring hormone rhythms over longer periods, particularly overnight. However, the wearable technology is not yet a routine diagnostic test for high blood pressure. The study was relatively small and was designed as a proof of concept.

More research is needed to determine how continuous hormone monitoring should be used in everyday clinical practice and whether it can improve diagnosis and treatment outcomes.

For now, the findings highlight an important point, and that is, a normal hormone reading at one moment does not always tell the complete story. Tracking how hormones change throughout the day and night may eventually help doctors uncover cases of primary aldosteronism.

Dr Eder Zavala, UKRI Future Leader Fellow at the University of Manchester and senior author of the study said: "A more detailed mathematical and computational analysis of daily hormonal profiles could eventually also help uncover earlier and more subtle forms of the disease, opening new opportunities to improve outcomes for patients living with high blood pressure."

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