Hypertension affects 47.7 percent of American adults — nearly half — but only 20.7 percent have it properly controlled. This complete guide explains what blood pressure numbers mean, the difference between primary and secondary hypertension (including sleep apnea and primary aldosteronism as frequently missed causes), the DASH diet evidence showing 8 to 14 mmHg systolic reduction, the full antihypertensive medicine class comparison, and the mechanism by which hypertension dir