Blood pressure is created by two forces working together: the amount of blood your heart pumps with each beat and the resistance that blood meets as it travels through your vessels. Every time your heart contracts, it pushes blood into your arteries, and the walls of those arteries push back. That interaction between flow and resistance is what produces the number on a blood pressure cuff.
The Two Forces Behind Every Reading
Blood pressure follows a simple relationship: it equals the volume of blood your heart pumps (cardiac output) multiplied by the resistance in your blood vessels. If either one goes up, blood pressure rises. If either one drops, blood pressure falls.
Cardiac output depends on how fast your heart beats and how much blood it ejects per beat. A heart pumping harder or faster sends more blood into the arteries, raising pressure. Peripheral resistance depends on the diameter of your blood vessels. When small arteries narrow, blood has to squeeze through a tighter space, which increases friction against the vessel walls and drives pressure up. When those same vessels relax and widen, pressure drops. Nearly every factor that affects blood pressure, from stress to salt to medications, works by changing one or both of these variables.
How Your Body Adjusts Pressure Minute to Minute
Your nervous system handles rapid, moment-to-moment adjustments. Sensors in your neck and chest called baroreceptors detect changes in arterial pressure and send signals to your brain. If pressure drops suddenly (say, when you stand up), your sympathetic nervous system fires, tightening blood vessels and speeding up your heart within seconds. The skeletal muscle vascular bed is so large that even small changes in its vessel tone can shift overall pressure significantly. In young men, research shows a strong correlation between sympathetic nerve activity and total peripheral resistance at rest.
Your body also releases a gas called nitric oxide inside blood vessels that counterbalances this tightening effect. When sympathetic activity is high, nitric oxide production ramps up to prevent excessive constriction. This back-and-forth keeps pressure within a livable range during normal daily activities.
The Kidney-Hormone System That Sets Long-Term Pressure
For longer-term control, your kidneys run a hormonal chain reaction. When blood pressure falls, your kidneys release an enzyme called renin. Renin breaks apart a protein made by your liver, producing a hormone that travels to the lungs and kidneys, where it gets converted into its active form. This active hormone narrows the walls of small arteries, immediately raising pressure. It also triggers your adrenal glands to release aldosterone and signals your brain to release antidiuretic hormone.
Together, aldosterone and antidiuretic hormone tell your kidneys to hold onto sodium and water. More fluid in your bloodstream means more blood volume, which increases cardiac output and raises pressure further. This system is why salt intake matters so much: the more sodium your kidneys retain, the more water follows, and the higher your blood volume climbs.
Why Salt and Potassium Are a Balancing Act
The typical Western diet is high in sodium and low in potassium, and that combination is particularly effective at raising blood pressure. Excess sodium causes your kidneys to retain water, increasing blood volume. It also triggers the smooth muscle cells lining your blood vessels to contract, raising peripheral resistance. The recommended daily sodium limit is less than 2,300 milligrams, roughly one teaspoon of table salt.
Potassium works in the opposite direction. It promotes sodium excretion through the kidneys, which reduces blood volume and lowers pressure. Research shows that increasing potassium intake favorably influences at least four of the body’s pressure-regulating feedback loops: the renin system, the aldosterone system, the sympathetic nervous system, and the sensitivity of baroreceptors. This is why foods rich in potassium (bananas, potatoes, beans, leafy greens) are consistently linked to lower blood pressure, and why the sodium-to-potassium ratio in your diet may matter more than sodium alone.
Lifestyle Factors That Raise Blood Pressure
About 90% of high blood pressure cases have no single identifiable cause. Instead, they result from a combination of lifestyle and genetic factors. A large cohort study identified six modifiable risk factors with strong evidence of causing hypertension: general obesity, abdominal obesity, excessive alcohol use, smoking, physical inactivity, and a poor diet. General obesity alone was enough to nearly double the risk of developing high blood pressure, with a hazard ratio of 1.86. Combined with smoking and physical inactivity, the risk climbed further.
Abdominal fat is especially relevant. For women, a waist circumference above 88 cm (about 35 inches) places them in the high-risk category. For men, the threshold is 102 cm (about 40 inches). Visceral fat around the organs drives inflammation and hormonal changes that stiffen arteries and increase sodium retention.
Genetics Account for Nearly Half the Picture
Studies estimate that 40% to 50% of the variation in blood pressure between people is heritable. If your parents had high blood pressure, your baseline risk is meaningfully higher than someone without that family history. However, the specific genes responsible remain largely unidentified. Known genetic variants explain less than 3% of blood pressure variation between individuals, which means hundreds or thousands of small genetic effects likely contribute, each one nudging pressure slightly. This also means that even with a strong genetic predisposition, lifestyle choices still influence a large portion of your risk.
How Aging Changes the Equation
As you age, the large arteries near your heart gradually lose their elasticity. The elastic fibers in artery walls break down and get replaced by stiffer collagen fibers. This process happens independently of plaque buildup and cholesterol. It’s a structural change in the vessel wall itself.
Healthy, elastic arteries act as a shock absorber. When the heart pumps, they stretch to accommodate the surge of blood, then gently recoil between beats. Stiff arteries can’t do this effectively, so the full force of each heartbeat hits the vessel walls without being cushioned. The result is a pattern called isolated systolic hypertension: the top number on your blood pressure reading rises while the bottom number stays the same or even drops. This is the most common form of high blood pressure in people over 60.
Medical Conditions That Directly Raise Pressure
In a smaller percentage of cases, high blood pressure is caused by an identifiable underlying condition. Kidney disease is the most common culprit. Damaged kidneys lose their ability to properly filter sodium and water, leading to fluid overload and increased blood volume. Diabetic kidney disease and chronic inflammation of the kidney’s filtering units are frequent triggers.
Endocrine disorders also play a role. A condition called primary aldosteronism causes the adrenal glands to produce too much aldosterone, forcing the kidneys to retain excess sodium. Tumors of the adrenal gland can flood the body with stress hormones that constrict blood vessels. Thyroid disorders and conditions involving excess growth hormone are rarer causes.
Obstructive sleep apnea deserves special mention. Repeated pauses in breathing during sleep trigger surges of sympathetic nervous system activity throughout the night, raising both heart rate and vessel constriction. Poor sleep quality alone has been shown to increase hypertension risk, and many people with resistant high blood pressure (pressure that doesn’t respond well to treatment) turn out to have undiagnosed sleep apnea.
Narrowing of the arteries that supply the kidneys, called renal artery stenosis, is another cause. In older adults this narrowing usually comes from atherosclerosis. In younger women, it more often results from abnormal growth of tissue in the artery wall.
Medications and Substances That Raise Pressure
Several common medications can push blood pressure up. Over-the-counter pain relievers like ibuprofen and naproxen cause the kidneys to retain sodium and water. Decongestants containing pseudoephedrine or phenylephrine directly constrict blood vessels. Oral contraceptives and hormone therapies containing estrogen can raise pressure in some women. ADHD medications, certain antidepressants, and oral steroids like prednisone are also known contributors.
Among recreational substances, cocaine and methamphetamine cause dramatic short-term spikes by flooding the body with signals that constrict vessels and accelerate the heart. Chronic alcohol use and nicotine both contribute to sustained elevations over time. Even some herbal supplements, including St. John’s wort and ephedra, can interfere with blood pressure regulation.