High blood pressure develops when the force of blood pushing against your artery walls stays consistently elevated, with readings at or above 130/80 mmHg. It rarely has a single cause. Instead, it typically results from a combination of factors: how your kidneys handle salt, how flexible your arteries are, how active your nervous system is, and what you eat and do every day. About half of all adults between 40 and 59 have it, and that number climbs to nearly 75% after age 60.
How Your Body Controls Blood Pressure
Your body has a built-in pressure regulation system that starts in the kidneys. When blood pressure drops, your kidneys release an enzyme called renin into your bloodstream. Renin triggers a chain reaction: it breaks apart a protein made by your liver, eventually producing a hormone that causes the muscular walls of small arteries to tighten. That same system also signals your adrenal glands to release a hormone that tells your kidneys to hold onto more sodium and water. More fluid in your bloodstream plus narrower arteries equals higher pressure.
In a healthy system, this process ramps up when pressure is low and dials back when pressure is normal. But when the system gets stuck in “on” mode, whether from kidney problems, excess weight, or other triggers, blood pressure stays elevated around the clock.
What Sodium Actually Does Inside Your Body
Sodium pulls water into your bloodstream. When you eat more salt than your body needs, your kidneys retain extra water to keep sodium concentrations balanced. That extra fluid increases the total volume of blood your heart has to pump, which raises the pressure on artery walls. Americans consume an average of 3,400 mg of sodium per day, well above the recommended limit of 2,300 mg.
Potassium works as sodium’s counterbalance. It helps your kidneys flush out excess sodium and relaxes blood vessel walls. Most people don’t get enough of it. The issue isn’t just how much salt you eat; it’s the ratio between sodium and potassium in your diet. Increasing potassium intake (through foods like bananas, potatoes, and leafy greens) can measurably lower blood pressure in people who already have hypertension.
How Arteries Stiffen Over Time
The inner lining of your blood vessels, called the endothelium, constantly releases chemicals that keep arteries relaxed and flexible. A healthy endothelium responds to flowing blood by lowering resistance throughout your vascular system. But when this lining gets damaged, whether by inflammation, high blood sugar, smoking, or simply aging, it stops producing enough of these relaxing signals. At the same time, it starts generating molecules that promote inflammation and constriction.
This creates a vicious cycle. Inflammation damages the endothelium, and a damaged endothelium triggers more inflammation. Over time, artery walls become stiffer and less able to expand when your heart pumps. Stiff arteries don’t absorb the pulse of each heartbeat the way flexible ones do, so the peak pressure (your systolic number) rises. This is a major reason blood pressure tends to increase with age, even in people who are otherwise healthy.
Sitting Too Much Raises Your Baseline
Physical inactivity doesn’t just miss an opportunity to lower blood pressure. It actively raises it. Prolonged sitting triggers a cascade of metabolic changes that push pressure upward through multiple pathways at once.
When you sit for hours, your sympathetic nervous system (the “fight or flight” branch) becomes overactive. Your body releases more stress hormones into your bloodstream, which constrict arteries and speed up your heart rate. At the same time, blood pools in your legs, causing fluid to shift into surrounding tissues. When you finally lie down at night, that fluid redistributes, and your body responds with another spike in nervous system activity, raising blood pressure even while you sleep.
Prolonged sitting also spikes blood sugar and insulin levels after meals more than moving does. Those elevated insulin levels tell your kidneys to hold onto sodium, compounding the pressure increase. When sitting is habitual, these effects accumulate into chronic changes: reduced insulin sensitivity, impaired blood vessel function, and sustained hypertension.
Insulin Resistance and Kidney Sodium Handling
Excess body weight, particularly around the midsection, often leads to a condition where your cells stop responding efficiently to insulin. Your pancreas compensates by producing more of it, flooding your bloodstream with higher-than-normal insulin levels. This matters for blood pressure because insulin directly stimulates your kidneys to reabsorb sodium at multiple points along the filtering process.
Insulin boosts sodium channels and transporters throughout the kidney, pulling salt (and the water that follows it) back into your bloodstream instead of letting it leave as urine. In people with normal insulin levels, this effect is modest. But when insulin is chronically elevated, as in obesity, metabolic syndrome, or type 2 diabetes, the sodium retention becomes significant enough to raise blood pressure on its own. This is one reason why losing weight often lowers blood pressure even before someone changes their salt intake.
Genetics Set the Stage
Heritability estimates for high blood pressure range from 25% to 60%, meaning your genes account for a substantial portion of your risk. Several specific gene pathways have been identified. Some affect how your kidneys handle sodium by influencing the activity of sodium channels. Others alter a protein that interacts with the sodium-potassium pump in your kidneys, heart, and brain, changing how efficiently your body moves salt in and out of cells. Still others affect the production of nitric oxide, the key molecule that relaxes blood vessels.
Having a genetic predisposition doesn’t guarantee you’ll develop hypertension. It means the threshold at which diet, weight, stress, and inactivity tip you into high blood pressure territory is lower than it is for someone without that genetic loading. If your parents had high blood pressure, the lifestyle factors described above carry more weight for you.
Medical Conditions That Directly Cause It
About 5% to 10% of hypertension cases have a specific, identifiable medical cause. The most common is obstructive sleep apnea, where repeated breathing pauses during sleep trigger surges of stress hormones that raise blood pressure overnight and eventually throughout the day. Narrowing of the arteries that supply the kidneys is the second most common cause; when kidneys sense reduced blood flow, they activate the same pressure-raising hormone cascade described earlier, but inappropriately.
A condition called primary aldosteronism, where the adrenal glands overproduce the hormone that drives sodium retention, is the third leading cause. Kidney disease itself is another, since damaged kidneys lose the ability to properly filter sodium and regulate fluid balance. Rare hormone-producing tumors round out the list. These secondary causes are worth investigating when blood pressure is unusually high, resistant to treatment, or develops suddenly in a young person.
Blood Pressure Categories
The American Heart Association defines four categories based on your readings:
- Normal: below 120/80 mmHg
- 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
The jump from “elevated” to Stage 1 can happen without any noticeable symptoms. About 22% of adults aged 18 to 39 already have hypertension, which means it is not exclusively a problem of middle and old age. Regular monitoring is the only way to catch it, since high blood pressure almost never produces symptoms until it has caused significant damage to the heart, kidneys, or blood vessels.