1.a.(2). Lifestyle Trials in Nonhypertensive Individuals
Rationale: A semiquantitative review (383) covering four of the acceptable studies (363, 366, 372, 374) in nonhypertensive individuals concluded that weight loss through dietary interventions significantly lowered blood pressure. In nonhypertensives, excluding one outlier trial that showed very large reductions in blood pressure (372),1 kg (2.2 lb) of weight loss was associated with a reduction of 0.45 mm Hg in both systolic and diastolic blood pressure. Since this review, published in 1991, almost all relevant studies have reported that weight loss reduces blood pressure in nonhypertensive individuals (364, 365, 367-371, 373, 375-380, 384).
The Trials of Hypertension Prevention Phase 1 (TOHP I) and Phase 2 (TOHP II) are among the larger, well-designed randomized trials, having follow-up rates exceeding 90 percent. They followed the participants for 18 months (378) and 3 to 4 years (379). The sample size of the weight loss intervention arms ranged from approximately 300 (TOHP I) to 600 (TOHP II). The populations were diverse, consisting of 30 to 35 percent women and 15 to 18 percent African Americans, and were recruited from 10 centers in TOHP I and 9 centers in TOHP II. Results from both TOHP I and TOHP II demonstrated that weight loss reduced blood pressure and the incidence of hypertension. Compared with controls, in both trials 10 kg (22 lb) of weight loss was associated with a reduction of 7 mm Hg systolic and 5 to 6 mm Hg diastolic blood pressure at 18 months. At 36 months, systolic and diastolic blood pressure was reduced by 6 and 4 mm Hg, respectively, for every 10 kg (22 lb) of weight loss (379). In addition, weight loss reduced the incidence of hypertension at 18 months by 20 to 50 percent (378, 379) and at 3 years by 19 percent (379). Secondary analyses from TOHP I (376) and analyses under way from TOHP II (385) demonstrated that the greater the weight loss, the greater the blood pressure reduction, and as long as weight loss was maintained, blood pressure remained reduced. One study that focused on older African American diabetics showed that weight loss of 2.4 kg (5.3 lb) at 6 months resulted in a reduction of 3.9 and 4.0 mm Hg systolic and diastolic blood pressure, respectively (362). Only one study in nonhypertensive individuals (368) showed inconsistent results, where weight reduction decreased systolic (significant) and diastolic (nonsignificant) blood pressure at 12 months in women but not in men. Another study (377) showed short-term (3 months) blood pressure reduction but no longer term (9 months) blood pressure reduction despite maintenance of weight loss of 9 kg (19.8 lb) (384).