Background: Patients with optimum (<120/80 mm Hg), normal (120-129/80-84 mm Hg), and high normal (130-139/85-89 mm Hg) blood pressure (BP) may progress to hypertension (≥140/90 mm Hg) over time. We aimed to establish the best frequency of BP screening by assessing the rates and determinants of progression to hypertension. Methods: We assessed repeated BP measurements in individuals without hypertension (BP<140/90 mm Hg) from the Framingham Study (4200 men, 5645 women; mean age 52 years) who attended clinic examinations during 1978-94. The incidence of hypertension (or use of antihypertensive treatment) and its determinants were studied. Findings: A stepwise increase in hypertension incidence occurred across the three non-hypertensive BP categories; 5.3% (95% CI 4.4-6.3%) of participants with optimum BP, 17.6% (15.2-20.3%) with normal, and 37.3% (33.3-41.5%) with high normal BP aged below age 65 years progressed to hypertension over 4 years. Corresponding 4-year rates of progression for patients 65 years and older were 16.0% (12.0-20.9), 25.5% (20.4-31.4), and 49.5% (42.6-56.4), respectively. Obesity and weight gain also contributed to progression; a 5% weight gain on follow-up was associated with 20-30% increased odds of hypertension. Interpretation: High normal BP and normal BP frequently progress to hypertension over a period of 4 years, especially in older adults. These findings support recommendations for monitoring individuals with high normal BP once a year, and monitoring those with normal BP every 2 years, and they emphasise the importance of weight control as a measure for primary prevention of hypertension.
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