High blood pressure develops when the force of blood pushing against your artery walls stays elevated over time, typically at or above 130/80 mmHg. For most people, there’s no single cause. It results from a combination of factors: how your body handles sodium, how stiff your arteries have become, how active your nervous system is, and how much extra weight you carry. About 90-95% of cases have no identifiable underlying disease, which is why high blood pressure often builds silently over years.
What the Numbers Mean
Blood pressure is measured in two numbers. The top number (systolic) reflects pressure when your heart contracts; the bottom number (diastolic) reflects pressure between beats. Under current guidelines from the American Heart Association:
- Normal: below 120/80
- Elevated: 120-129 systolic with diastolic still below 80
- Stage 1 hypertension: 130-139 systolic or 80-89 diastolic
- Stage 2 hypertension: 140+ systolic or 90+ diastolic
These thresholds were lowered in 2017, which means millions of people who previously had “normal” readings were reclassified. If your numbers land in the elevated range, you’re not yet hypertensive, but the trajectory matters. Elevated readings rarely improve on their own without changes.
How Sodium Raises Blood Pressure
The classic explanation is straightforward: when you eat more sodium than your kidneys can efficiently clear, your body holds onto extra water to dilute it. That extra fluid increases the volume of blood circulating through your vessels, which raises pressure against the artery walls. This relationship between sodium and fluid retention is one of the most well-established mechanisms in blood pressure regulation.
Recent research has complicated the picture somewhat. The body doesn’t simply accumulate water in lockstep with sodium. Significant amounts of sodium can be stored in tissues, particularly the skin, bound to structural molecules called glycosaminoglycans. This means your body has a kind of sodium reservoir that can buffer some excess intake. But this system has limits. When sodium intake consistently exceeds what your body can store or excrete, the fluid-volume effect wins out and pressure climbs.
Most adults consume well over 3,400 mg of sodium per day, far beyond the 2,300 mg general recommendation. The bulk of it comes not from the salt shaker but from processed foods, restaurant meals, bread, and cured meats.
How Your Arteries Stiffen With Age
Aging is the single most powerful predictor of high blood pressure, and the reason is physical: your arteries lose their ability to flex. In younger people, large arteries like the aorta stretch when the heart pumps blood and then recoil between beats, smoothing out pressure fluctuations. Over decades, the elastic fibers in artery walls fragment and fray, calcium deposits accumulate, and collagen fibers multiply and stiffen. The result is a vessel that resists stretching.
Studies measuring arterial compliance across age groups have found that large artery flexibility drops by roughly 35-46% over a lifetime, while smaller artery flexibility drops by as much as 83-90%. This is a dramatic decline that directly translates into higher systolic pressure, which is why isolated high systolic readings become so common after age 60. One driving factor behind this stiffening is reduced production of nitric oxide, a molecule your artery lining releases to keep vessels relaxed and pliable. As nitric oxide output falls with age, arteries constrict more easily and their walls thicken, adding both a functional and structural component to rising pressure.
How Excess Weight Drives Up Pressure
Carrying extra weight, particularly around the abdomen, activates the sympathetic nervous system, your body’s “fight or flight” wiring. Visceral fat (the deep belly fat surrounding your organs) is especially problematic. Research measuring nerve activity found that sympathetic nerve firing rates are 55% higher in men with high abdominal fat compared to men whose extra weight is distributed under the skin elsewhere. In men with only subcutaneous fat, nerve activity was no different from lean men.
This heightened nerve activity does two things. First, it signals the kidneys to retain more sodium and water, expanding blood volume. Second, it constricts blood vessels in the muscles, reducing blood flow. That vessel constriction may also be the primary driver of insulin resistance in people with obesity, because less blood reaching the muscles means less glucose delivery. So the metabolic problems of obesity and the blood pressure problems are likely two branches of the same underlying issue: an overactive sympathetic nervous system triggered by visceral fat.
Your Body’s Pressure-Regulating Hormones
Your body runs a built-in system for adjusting blood pressure called the renin-angiotensin-aldosterone system. Here’s how it works in simple terms: your kidneys release an enzyme that kicks off a chain reaction, ultimately producing a hormone called angiotensin II. This hormone constricts blood vessels (raising resistance) and signals the adrenal glands to release aldosterone. Aldosterone then tells the kidneys to reabsorb more sodium and water, increasing blood volume.
In a healthy body, this system activates when blood pressure drops too low and dials back when pressure is adequate. In hypertension, the system can become overactive or poorly regulated. The blood vessels stay constricted, the kidneys keep holding sodium, and pressure remains elevated even when the body doesn’t need it. This is why several of the most common blood pressure medications target different steps in this hormonal chain.
Sleep Apnea and Blood Pressure
Obstructive sleep apnea is one of the most underrecognized contributors to high blood pressure. During sleep, the airway repeatedly collapses, cutting off airflow for seconds at a time. Each episode triggers a cascade of stress signals: oxygen levels drop, carbon dioxide rises, the lungs stop inflating normally, and the brain jolts partially awake to restart breathing. All four of these stimuli activate the sympathetic nervous system simultaneously.
Over the course of a night, this happens dozens or even hundreds of times. The cumulative effect is persistent sympathetic overdrive that doesn’t reset when morning comes. People with untreated sleep apnea typically show a “non-dipping” pattern, meaning their blood pressure fails to drop during sleep the way it normally should. The combination of oxygen deprivation and stress hormones released during these episodes, including endothelin, a potent vessel constrictor, eventually elevates daytime blood pressure as well. If your blood pressure is hard to control despite medication, sleep apnea is one of the first things worth investigating.
Medications That Raise Blood Pressure
Several common over-the-counter and prescription drugs can push blood pressure up, sometimes significantly. The most frequently encountered culprits include:
- Pain relievers (NSAIDs): Ibuprofen (Advil) and naproxen (Aleve) cause the body to retain sodium and fluid. Regular use can meaningfully raise readings.
- Decongestants: Pseudoephedrine and phenylephrine, found in many cold and sinus products, constrict blood vessels.
- Hormonal birth control: Most pills and patches carry warnings about blood pressure as a potential side effect.
- Antidepressants: Several classes, including SSRIs, tricyclics, and MAO inhibitors, can affect blood pressure.
- Stimulants: ADHD medications and high-dose caffeine both activate the sympathetic nervous system.
- Herbal supplements: Licorice root, ginseng, ephedra, and guarana can all interfere with blood pressure regulation.
Recreational drugs like cocaine, methamphetamine, and ecstasy cause acute and sometimes dangerous spikes. If you’re tracking high readings and use any of these substances or medications regularly, that’s worth considering as a contributing factor.
Medical Conditions That Cause Hypertension
In roughly 5-10% of cases, high blood pressure is caused by an identifiable underlying condition. This is called secondary hypertension, and treating the root cause can sometimes resolve the blood pressure problem entirely.
Kidney disease is the most common culprit. Damaged kidneys lose the ability to properly filter sodium and regulate fluid balance. This includes damage from diabetes, polycystic kidney disease, and inflammation of the kidney’s filtering units. Narrowed arteries leading to the kidneys (from plaque buildup or a structural condition called fibromuscular dysplasia) can also trigger high blood pressure by tricking the kidneys into thinking blood flow is too low, prompting them to retain more fluid.
Hormonal conditions account for another important subset. Overactive adrenal glands can produce too much aldosterone, causing the kidneys to hold sodium and water aggressively. A rare adrenal tumor called a pheochromocytoma floods the body with adrenaline, causing dramatic pressure spikes. Cushing syndrome, where cortisol levels stay chronically elevated, also raises blood pressure. Even overactive parathyroid glands, which raise calcium levels in the blood, can push pressure up.
A structural heart defect present from birth, coarctation of the aorta, forces the heart to pump harder to push blood past a narrowed section of the body’s main artery. And pregnancy can either worsen pre-existing hypertension or trigger new-onset high blood pressure, sometimes progressing to preeclampsia.
Secondary hypertension is worth suspecting if your blood pressure develops suddenly, is unusually high for your age, or doesn’t respond well to standard treatment.