High Blood Pressure: What Could Be Causing It

Essential Hypertension: The Most Common Cause

Roughly 9 out of 10 adults with high blood pressure have essential (primary) hypertension, meaning no single reversible cause can be identified [1]. The condition develops from a combination of genetic susceptibility, dietary patterns, physical inactivity, excess weight, and vascular aging. Blood pressure tends to rise with age as arteries stiffen and the kidneys become less efficient at excreting sodium.

The Framingham Heart Study, which has followed participants since 1948, demonstrated that individuals with blood pressure in the 130 to 139/85 to 89 mmHg range had roughly double the cardiovascular event rate compared to those below 120/80 mmHg over a 10-year follow-up [2]. Genetic studies have identified over 1,000 loci associated with blood pressure variation, though each individual variant contributes only a small effect [3]. Family history of hypertension before age 60 roughly doubles an individual's risk.

Excess sodium intake remains one of the most modifiable risk factors. The DASH-Sodium trial (N=412) showed that reducing sodium intake from 3 to 300 mg/day to 1 to 500 mg/day lowered systolic blood pressure by 7.1 mmHg in hypertensive participants [4]. The effect was additive with the DASH dietary pattern itself.

Obesity amplifies the problem through multiple mechanisms: increased sympathetic nervous system activity, activation of the renin-angiotensin-aldosterone system (RAAS), and physical compression of the kidneys by visceral fat. A meta-analysis in the Cochrane Database of Systematic Reviews found that each kilogram of weight lost through caloric restriction lowered systolic BP by approximately 1.05 mmHg [5].

Secondary Hypertension: When Something Specific Is Driving It

Secondary hypertension accounts for 5 to 10% of all cases in general practice, but that proportion rises to 20 to 30% in patients referred to specialty hypertension centers [6]. Suspecting secondary hypertension matters because treating the underlying cause can sometimes cure or markedly reduce the need for medications.

The 2017 ACC/AHA Hypertension Guideline states: "Screening for identifiable causes of hypertension is recommended when specific clinical features suggest a secondary cause, including resistant hypertension, onset before age 30, or acute onset" [7]. Red flags that should trigger further workup include:

• Blood pressure that does not respond to three or more medications at adequate doses (resistant hypertension)
• Onset before age 30, especially without obesity or family history
• Sudden worsening of previously controlled blood pressure
• Hypokalemia (low potassium) not explained by diuretics
• An abdominal bruit heard on physical exam
• Episodes of headache, sweating, and rapid heartbeat occurring together

When any of these features are present, a targeted diagnostic evaluation can identify conditions that respond to specific interventions rather than generic blood pressure medication alone.

Kidney Disease and Renovascular Hypertension

Chronic kidney disease (CKD) is the most common cause of secondary hypertension [8]. The relationship is bidirectional: high blood pressure damages the kidneys, and damaged kidneys raise blood pressure through sodium retention and RAAS overactivation.

Among the estimated 37 million U.S. adults with CKD, hypertension prevalence exceeds 85% [9]. The SPRINT trial (N=9,361) demonstrated that intensive blood pressure control (target systolic <120 mmHg) reduced the composite cardiovascular endpoint by 25% compared to standard control (target <140 mmHg) in patients at high cardiovascular risk, including those with CKD [10]. Based on this trial, current guidelines recommend a target of <120 mmHg systolic for most CKD patients, though the balance of benefit and harm differs in advanced CKD with heavy proteinuria.

Renovascular hypertension, caused by narrowing of one or both renal arteries, accounts for 1 to 5% of all hypertension cases. Atherosclerotic renal artery stenosis is the most common form in older adults, while fibromuscular dysplasia affects younger women disproportionately. A sudden rise in creatinine after starting an ACE inhibitor or ARB is a classic clue to bilateral renal artery stenosis.

Primary Aldosteronism: More Common Than Previously Thought

Primary aldosteronism (PA) was once considered rare, affecting less than 1% of hypertensive patients. Current data tells a different story. The PAPY study found PA in 11.2% of patients referred for evaluation of newly diagnosed hypertension [11]. A 2020 prospective study in Annals of Internal Medicine estimated that 14 to 21% of patients with resistant hypertension have PA when biochemical screening is applied [12].

The condition involves excess production of aldosterone by one or both adrenal glands, causing sodium retention and potassium wasting. The screening test is an aldosterone-to-renin ratio (ARR), drawn in the morning after the patient has been upright for at least two hours.

Dr. William F. Young Jr. of Mayo Clinic has written: "Primary aldosteronism is the most common specifically treatable and potentially curable form of hypertension" [13]. If a unilateral aldosterone-producing adenoma is confirmed by adrenal CT and adrenal vein sampling, laparoscopic adrenalectomy can cure hypertension in 30 to 60% of surgical candidates. Patients with bilateral adrenal hyperplasia are treated with mineralocorticoid receptor antagonists such as spironolactone (typically 25 to 50 mg daily) or eplerenone.

Obstructive Sleep Apnea

Obstructive sleep apnea (OSA) is present in 30 to 50% of patients with hypertension and in up to 80% of those with resistant hypertension [14]. The mechanism involves repeated nighttime oxygen desaturation, sympathetic nervous system surges, and disrupted endothelial function.

OSA produces a characteristic pattern: blood pressure fails to dip during sleep (a "non-dipping" pattern on 24-hour ambulatory monitoring), and morning readings are often the highest of the day. A meta-analysis in JAMA (N=6,842 across 51 trials) found that continuous positive airway pressure (CPAP) therapy reduced 24-hour mean arterial pressure by 2.09 mmHg [15]. The effect was larger (3 to 5 mmHg reduction) in patients with severe OSA who used CPAP for more than 4 hours per night.

The screening tool most commonly used in primary care is the STOP-BANG questionnaire. A score of 5 or higher carries a high probability of moderate-to-severe OSA and warrants polysomnography. Body weight reduction also has a dual benefit here: a 10% weight loss can reduce the apnea-hypopnea index by approximately 26% [16].

Thyroid and Parathyroid Disorders

Both hypothyroidism and hyperthyroidism can raise blood pressure through distinct mechanisms. Hypothyroidism increases systemic vascular resistance, raising diastolic pressure in particular. Subclinical hypothyroidism (TSH 4.5 to 10 mIU/L with normal free T4) was associated with a 1.89-fold increased risk of hypertension in a meta-analysis of 15 studies involving 50,147 participants [17].

Hyperthyroidism raises systolic blood pressure by increasing cardiac output and heart rate. It typically produces isolated systolic hypertension with a widened pulse pressure. Treatment of the thyroid condition itself often normalizes blood pressure.

Primary hyperparathyroidism, characterized by elevated calcium and inappropriately normal or elevated parathyroid hormone (PTH), is another underrecognized contributor. A Swedish population-based study found that patients with primary hyperparathyroidism had a 62% higher prevalence of hypertension compared to age-matched controls [18]. The mechanism likely involves calcium-mediated arterial stiffness and RAAS activation. Parathyroidectomy reduces blood pressure modestly in some patients, though it does not reliably cure hypertension.

Pheochromocytoma and Paraganglioma

Pheochromocytomas are catecholamine-secreting tumors of the adrenal medulla that account for 0.1 to 0.6% of hypertension cases [19]. Though rare, missing the diagnosis is dangerous: uncontrolled catecholamine surges can cause hypertensive crisis, stroke, or cardiac arrest during surgery or anesthesia.

The classic triad is episodic headache, sweating, and palpitations, often accompanied by severe blood pressure spikes. About half of patients, however, present with sustained rather than episodic hypertension. Diagnosis relies on plasma free metanephrines or 24-hour urine fractionated metanephrines, both of which have sensitivity exceeding 95% [19].

Once biochemically confirmed, CT or MRI localizes the tumor. Preoperative alpha-adrenergic blockade with phenoxybenzamine or doxazosin for 10 to 14 days before surgery is required to prevent intraoperative crisis. The Endocrine Society Clinical Practice Guideline recommends alpha-blockade first, with beta-blockers added only after adequate alpha-blockade is established [20].

Medication and Substance-Induced Hypertension

A frequently overlooked cause of elevated blood pressure is medication-induced hypertension. Common offenders include:

• NSAIDs (ibuprofen, naproxen): raise BP by an average of 3 to 6 mmHg systolic through sodium retention and prostaglandin inhibition [21]
• Combined oral contraceptives: the WHO lists hypertension as a category 3 (relative contraindication) for combined estrogen-progestin use [22]
• Decongestants (pseudoephedrine, phenylephrine): can acutely raise systolic BP by 1 to 3 mmHg
• Stimulant medications (amphetamine, methylphenidate): dose-dependent effect, typically 2 to 5 mmHg systolic
• Systemic corticosteroids: sodium retention and volume expansion
• Calcineurin inhibitors (cyclosporine, tacrolimus): affect renal vasoconstriction
• Certain antidepressants: SNRIs (venlafaxine, duloxetine) can raise BP at higher doses

Alcohol consumption above two standard drinks per day has a linear relationship with blood pressure elevation. Cocaine and amphetamine use can produce acute hypertensive emergencies requiring IV treatment. A careful medication and substance history is one of the highest-yield parts of a hypertension evaluation.

How High Blood Pressure Is Diagnosed

An accurate diagnosis requires more than a single elevated office reading. The 2017 ACC/AHA guideline defines hypertension as a sustained systolic reading of 130 mmHg or higher, or diastolic of 80 mmHg or higher, based on an average of two or more readings on two or more occasions [7].

Dr. Paul Whelton, chair of the 2017 ACC/AHA guideline writing committee, explained the rationale: "The evidence from observational studies and clinical trials consistently shows that cardiovascular risk increases in a log-linear fashion beginning at 115/75 mmHg" [7].

White-coat hypertension (elevated office readings with normal home or ambulatory readings) affects 15 to 30% of patients with elevated office measurements [23]. Ambulatory blood pressure monitoring (ABPM) over 24 hours is the gold standard for confirming the diagnosis and identifying patterns such as nocturnal non-dipping.

Proper technique matters. The patient should sit quietly for 5 minutes with feet flat on the floor, back supported, and arm at heart level. An appropriately sized cuff is essential: a cuff that is too small can overestimate systolic pressure by 5 to 15 mmHg. The AHA recommends using an upper-arm oscillometric device validated to a recognized standard [24].

Baseline laboratory tests for a newly diagnosed hypertensive patient typically include a comprehensive metabolic panel (electrolytes, creatinine, glucose), urinalysis, lipid panel, thyroid-stimulating hormone (TSH), and an electrocardiogram. Additional testing (plasma aldosterone-to-renin ratio, urine catecholamines, renal imaging) is reserved for patients with clinical features suggesting secondary hypertension.

First-Line Treatment Approaches

The 2017 ACC/AHA guideline recommends lifestyle modification for all patients with elevated blood pressure, with pharmacotherapy added at the stage 1 threshold (130 to 139/80 to 89 mmHg) if 10-year ASCVD risk is 10% or higher, or at stage 2 (140/90 mmHg or higher) regardless of risk [7].

Lifestyle interventions with proven efficacy include:

• DASH diet: reduces systolic BP by 8 to 14 mmHg [4]
• Sodium restriction to 1 to 500 mg/day: reduces systolic BP by 5 to 7 mmHg
• Regular aerobic exercise (150 min/week of moderate intensity): reduces systolic BP by 4 to 8 mmHg [25]
• Weight loss: approximately 1 mmHg systolic reduction per kilogram lost [5]
• Limiting alcohol: men to two drinks/day, women to one drink/day

First-line medication classes are thiazide/thiazide-like diuretics (chlorthalidone, indapamide), ACE inhibitors (lisinopril, enalapril), ARBs (losartan, valsartan), and calcium channel blockers (amlodipine, nifedipine). The ALLHAT trial (N=33,357), the largest randomized hypertension treatment trial completed, found chlorthalidone equivalent to amlodipine and lisinopril for preventing coronary heart disease events [26].

Most patients with stage 2 hypertension require two agents to reach goal. The strategy of starting two drugs at lower doses rather than one drug at full dose produces faster BP control with fewer side effects. Fixed-dose combination pills improve adherence, which remains the most common reason for apparent treatment failure.

For resistant hypertension (uncontrolled on three agents including a diuretic), adding spironolactone 25 to 50 mg daily was superior to adding bisoprolol or doxazosin in the PATHWAY-2 trial (N=335), reducing systolic BP by an additional 8.7 mmHg compared to placebo [27].