All normotensive participants and hypertensive patients were screened at the physical examination center and hypertension clinic at Anzhen Hospital. A total of 495 healthy, normotensive subjects (NT group) and 490 hypertensive patients (EH group) were screened. Blood pressure (BP) was accurately measured three times on different days with a mercury sphygmomanometer by experienced internists in their office. Measurements were taken after the patients had been seated on a chair with their feet on the floor and their arms supported at heart level for 10 min. The definition of normotension (SBP < 130 mmHg and DBP < 85 mmHg) and hypertension (140 ≤ SBP ≤ 179 mmHg, or 90 ≤ DBP ≤ 109 mmHg) were based on the BP classification of the seventh report of the Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure (JNC-VII). All hypertensive patients were diagnosed as having essential hypertension and had never been treated with any antihypertensive drugs.