High blood pressure happens when the force of blood pushing against your artery walls stays too high over time. A reading of 130/80 mm Hg or above is now classified as hypertension. In about 90% to 95% of cases, there’s no single identifiable cause. Instead, a combination of genetics, diet, body weight, stress, aging, and daily habits gradually pushes pressure upward.
How Your Body Regulates Blood Pressure
Your body has a built-in pressure control system that involves your kidneys, blood vessels, and hormones all working together. The most important of these is a hormone chain reaction that starts in the kidneys. When your kidneys sense low blood flow, they release an enzyme that triggers the production of a powerful vessel-constricting hormone. That same chain reaction also signals your adrenal glands to release aldosterone, a hormone that tells your kidneys to hold onto sodium and water, increasing blood volume.
In healthy people, this system ramps up when pressure drops and dials back when pressure is adequate. In hypertension, the system can become overactive. More than 90% of the vessel-constricting hormone in your tissues is produced locally in organ walls rather than circulating through your bloodstream. This means the pressure-raising effects can be happening right inside your arteries, heart, and kidneys even when standard blood tests look normal. On the artery wall itself, this hormone triggers constriction, inflammation, tissue growth, and remodeling, all of which make vessels narrower and stiffer over time.
Sodium, Potassium, and Fluid Balance
Too much sodium and too little potassium is one of the most common drivers of high blood pressure. Sodium pulls water into your bloodstream, increasing the total volume of blood your heart has to pump. Americans consume an average of 3,400 mg of sodium per day, well above the recommended ceiling of 2,300 mg.
Potassium works as sodium’s counterbalance, helping your kidneys flush out excess sodium and relaxing blood vessel walls. Most people don’t get enough of it. When the ratio between these two minerals tips too far toward sodium, your body retains more fluid, your blood volume rises, and your arteries face more pressure with every heartbeat. Increasing potassium intake through fruits, vegetables, and legumes can measurably lower blood pressure, especially if it’s already elevated.
Genetics and Family History
Blood pressure runs in families. Twin studies estimate heritability at roughly 60% for males and 30% to 40% for females. Family studies put the figure at 15% to 35% overall. That doesn’t mean hypertension is inevitable if your parents had it, but it does mean your threshold for developing it may be lower. You might need less sodium, less weight gain, or less stress before your numbers start climbing compared to someone without a family history.
How Aging Stiffens Your Arteries
Young, healthy arteries are elastic. They stretch when your heart pumps and spring back between beats, which cushions the pressure. With age, the elastic fibers in artery walls break down and get replaced by stiffer collagen. Inflammation, oxidized cholesterol particles, and years of exposure to high blood sugar accelerate this process by promoting collagen cross-linking and breaking down elastin even faster.
This stiffening is the main reason systolic pressure (the top number) tends to climb steadily after age 50 while diastolic pressure (the bottom number) may actually drop. The result is a wider gap between the two numbers, called pulse pressure, which is itself an independent risk factor for heart attack and stroke. Arterial stiffness is now recognized as a major cardiovascular risk factor on its own.
Body Weight and Physical Inactivity
As body weight increases, the total volume of blood circulating through your body also increases. More blood flowing through the same network of arteries creates more force on those walls. Excess body fat, particularly around the midsection, also promotes inflammation and disrupts hormone signaling in ways that keep blood pressure elevated.
The good news is that the relationship works in reverse too. A meta-analysis of randomized controlled trials found that systolic blood pressure drops about 1 mm Hg for every kilogram (roughly 2.2 pounds) of weight lost, with a similar reduction in diastolic pressure. Losing 10 kg could mean a 10-point drop in your systolic reading, which is comparable to what some medications achieve. Regular aerobic exercise lowers pressure independently of weight loss by improving how well your arteries dilate and reducing the overactivity of your nervous system’s “fight or flight” response.
Sleep Apnea and Chronic Stress
Obstructive sleep apnea is one of the most underdiagnosed causes of high blood pressure. During sleep, the airway repeatedly collapses, cutting off oxygen for seconds at a time. Each drop in oxygen triggers a surge of adrenaline and activates the same kidney-based hormone system that raises blood pressure. Among people with resistant hypertension (blood pressure that stays high despite three or more medications), sleep apnea is present in roughly 82% of cases. In those with truly refractory hypertension, the prevalence approaches 100%.
Chronic psychological stress keeps your sympathetic nervous system, the branch responsible for the fight-or-flight response, running at a higher baseline. Over months and years, this sustained nervous system activation raises resting heart rate, constricts blood vessels, and tells the kidneys to retain more sodium. The effect compounds when stress leads to poor sleep, overeating, increased alcohol use, or less physical activity.
Alcohol and Caffeine
Alcohol raises blood pressure in a dose-dependent way. A large meta-analysis of cohort studies found that hypertension risk increases meaningfully above about 12 grams of alcohol per day in men (roughly one standard drink) and 24 grams per day in women (about two drinks). The more you drink beyond those thresholds, the steeper the risk climbs. Cutting back on heavy drinking can produce blood pressure reductions within weeks.
Caffeine causes a short-term spike in blood pressure, typically lasting a few hours. For habitual coffee drinkers, tolerance develops and the effect becomes smaller, but in some people it remains significant. If your blood pressure is borderline, checking it before and after your morning coffee can tell you whether caffeine is a meaningful contributor for you.
Medications That Raise Blood Pressure
Several common over-the-counter and prescription medications can push blood pressure up, sometimes without people realizing it. The most frequent culprits include:
- Pain relievers like ibuprofen and naproxen. These cause your body to retain sodium and reduce blood flow to the kidneys, which raises pressure. Occasional use is usually fine, but daily use for weeks can have a real impact.
- Decongestants such as pseudoephedrine and phenylephrine, found in many cold and sinus products. They work by constricting blood vessels in your nose, but they constrict blood vessels everywhere else too.
- Hormonal birth control. Birth control pills and some hormonal devices can raise blood pressure in some women, particularly those with other risk factors.
- Certain antidepressants, including older classes like tricyclics and MAO inhibitors, as well as some newer SSRIs.
- ADHD stimulant medications like methylphenidate.
- Herbal supplements including licorice root, ginseng, guarana, and ephedra (ma-huang), which are sometimes marketed for energy or weight loss.
If you’re taking any of these regularly and your blood pressure has crept up, the medication may be part of the equation.
Medical Conditions That Cause Hypertension
In 5% to 10% of cases, high blood pressure has a specific, identifiable medical cause. This is called secondary hypertension, and treating the underlying condition can sometimes resolve the blood pressure problem entirely.
Kidney disease is the most common trigger. Diabetes can damage the kidneys’ filtering system over time, leading to fluid and sodium retention. Polycystic kidney disease, an inherited condition where cysts grow on the kidneys, also raises pressure. Narrowing of the arteries that supply the kidneys (from fatty plaque buildup or a condition called fibromuscular dysplasia) reduces blood flow and tricks the kidneys into activating that pressure-raising hormone system as if the whole body needs more blood.
Hormone-producing tumors and gland disorders account for another important category. The adrenal glands can overproduce aldosterone, causing the kidneys to hold onto far too much sodium and water. A rare adrenal tumor called a pheochromocytoma floods the body with adrenaline, causing dramatic pressure spikes. Cushing syndrome, where cortisol levels stay chronically elevated, raises blood pressure through multiple pathways. Both overactive and underactive thyroid conditions can contribute, as can overactive parathyroid glands, which raise calcium levels and, in turn, blood pressure.
Blood Pressure Categories
Understanding where your numbers fall helps you gauge your personal risk:
- Normal: below 120/80 mm Hg
- Elevated: 120 to 129 systolic with diastolic still below 80
- Stage 1 hypertension: 130 to 139 systolic, or 80 to 89 diastolic
- Stage 2 hypertension: 140 or higher systolic, or 90 or higher diastolic
Elevated blood pressure is the warning zone. Without changes, most people in this range progress to stage 1 within a few years. The causes described above rarely act alone. For most people, high blood pressure is the result of several factors layering on top of each other: a genetic predisposition, a few extra pounds, too much sodium, not enough movement, and arteries that are gradually losing their flexibility with age. Addressing even one or two of those factors can be enough to shift your numbers in the right direction.