Elevated blood pressure results from a combination of factors, and in 85% to 95% of cases, no single identifiable cause exists. An estimated 1.4 billion adults worldwide have hypertension, representing 33% of people aged 30 to 79. Nearly half of them don’t know it. Understanding what drives blood pressure upward helps explain why it’s so common and what you can do about it.
How Blood Pressure Categories Are Defined
The 2025 guidelines from the American Heart Association and American College of Cardiology define four categories based on readings taken in a healthcare setting:
- 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
If your top and bottom numbers fall into different categories, the higher category applies. A reading of 135/75, for instance, counts as Stage 1 hypertension because of the systolic number, even though the diastolic looks normal.
Primary Hypertension: The Most Common Type
Primary (also called essential) hypertension accounts for the vast majority of cases. It develops gradually over years without a single traceable cause. Instead, it arises from the interplay of genetics, diet, body weight, physical activity, and the slow changes that happen inside blood vessels as you age.
Your body regulates blood pressure through a system that starts in the kidneys. When pressure drops, the kidneys release a signal that triggers a chain reaction: your liver produces a protein, your lungs and kidneys convert it into an active hormone, and that hormone tightens blood vessels while telling the kidneys to hold onto more salt and water. The result is higher pressure. In people with primary hypertension, this system can become overactive or fail to dial back down properly, keeping pressure persistently elevated.
How Sodium and Potassium Interact
Sodium gets most of the attention, but the balance between sodium and potassium matters more than sodium alone. When your potassium intake is low, the kidneys activate a transporter that reabsorbs more sodium chloride, holding onto salt and water that would otherwise be excreted. Even a short period of low potassium intake, as little as 12 hours, can ramp up this salt-retaining mechanism.
This means two people eating the same amount of salt can have very different blood pressure responses depending on how much potassium they consume. Fruits, vegetables, beans, and potatoes are rich in potassium. A diet heavy in processed food tends to be high in sodium and low in potassium simultaneously, which is a particularly effective recipe for pushing pressure upward.
Genetics and Family History
Hypertension runs in families, and having two parents with high blood pressure raises your risk more than having one. More than 100 genetic variations have been linked to essential hypertension. Many of these variants affect the same kidney-based pressure regulation system described above, while others influence the health of blood vessel linings.
A handful of rare genetic disorders cause hypertension more directly by disrupting the body’s salt and fluid balance. These conditions, including familial hyperaldosteronism and Liddle syndrome, typically cause high blood pressure at a younger age and are often resistant to standard treatments. They account for a small fraction of total cases but are important to identify because they require specific management.
Insulin Resistance and Metabolic Health
People with insulin resistance, a condition where cells stop responding normally to insulin, often develop high blood pressure. The connection is surprisingly direct. When the body becomes resistant to insulin’s effect on blood sugar, it compensates by producing more insulin. That extra insulin still works perfectly well in one specific location: the kidneys. There, it enhances salt reabsorption in the kidney’s filtration tubes, creating a state of salt overload that raises blood pressure. This mechanism helps explain why hypertension, prediabetes, and excess abdominal weight so frequently travel together.
Arterial Stiffness and Aging
Blood vessels are elastic when you’re young. With each heartbeat, the large arteries expand to absorb the pulse of pressure, then recoil to keep blood flowing smoothly between beats. Over decades, the elastic fibers in artery walls break down and get replaced by stiffer collagen. The vessel walls also accumulate calcium deposits. The result is arteries that can no longer flex as easily, forcing the heart to push against more resistance.
This is why systolic pressure (the top number) tends to climb with age even in otherwise healthy people. By the time someone reaches their 60s or 70s, isolated systolic hypertension, where the top number is high but the bottom number remains normal or even drops, becomes the dominant pattern. It’s a mechanical problem rooted in the physical structure of the arteries themselves.
Secondary Causes: When Something Specific Is to Blame
In roughly 5% to 15% of cases, high blood pressure stems from an identifiable condition. This is called secondary hypertension, and treating the underlying cause can sometimes resolve the blood pressure problem entirely.
Kidney artery narrowing is one classic trigger. When the arteries supplying the kidneys become partially blocked, the kidneys sense reduced blood flow and respond as though the entire body’s pressure is too low. They activate the salt-and-water-retention system at full force, driving pressure up throughout the body even though the real problem is localized to the kidney’s own blood supply.
Obstructive sleep apnea is another common contributor. Repeated episodes of oxygen deprivation during sleep trigger surges of stress hormones that constrict blood vessels and raise heart rate. Over time, these nightly spikes translate into elevated daytime readings as well. Adrenal gland tumors, thyroid disorders, and certain hormonal conditions round out the list of secondary causes.
Medications and Supplements That Raise Pressure
Several common medications can push blood pressure upward, sometimes without you realizing it. Pain relievers like ibuprofen and naproxen cause the kidneys to retain sodium and water in a dose-dependent way. In one study of arthritis patients, 16.6% developed hypertension while taking anti-inflammatory drugs.
Other culprits include:
- Decongestants containing pseudoephedrine, which raise systolic pressure modestly and increase heart rate by about 3 beats per minute
- Oral contraceptives, which can raise systolic pressure by 3 to 6 points and cause new hypertension in roughly 5% of women
- Corticosteroids like prednisone, which cause sodium retention and fluid buildup
- Certain antidepressants, particularly those that affect norepinephrine. At higher doses, one common SNRI causes clinically significant blood pressure increases in 13% of patients
- Supplements including natural licorice, yohimbine, and some ginseng products
Even caffeine produces a small, measurable bump of about 2 points systolic per dose, though regular users develop some tolerance. If your blood pressure has crept up and you take any of these regularly, the medication itself could be a contributing factor worth discussing with your provider.
How Multiple Causes Layer Together
For most people, elevated blood pressure isn’t caused by one thing. It’s the sum of several forces pushing in the same direction. A genetic predisposition might raise your baseline risk. A high-sodium, low-potassium diet compounds it. Weight gain introduces insulin resistance, which amplifies kidney salt retention. Aging stiffens your arteries, adding a mechanical load. A daily anti-inflammatory for joint pain layers on additional sodium retention. None of these alone might push you past the threshold, but together they can move your readings from normal to elevated to Stage 1 over the course of years.
This layering effect also explains why small changes in multiple areas, losing a modest amount of weight, increasing potassium-rich foods, reducing sodium, staying physically active, can collectively bring pressure down more effectively than tackling any single factor in isolation.