Weight-reducing diets for people with elevated blood pressure

Compared to the general population, people with high blood pressure have a higher risk of death and complications such as heart attack or stroke. Dietary interventions to lower body weight are commonly recommended as a first therapeutic step for overweight people with high blood pressure, based on the association of increased weight and increased blood pressure. However, whether weight loss has a long-term effect on blood pressure and reduces the adverse effects of elevated blood pressure remains unclear.

As only randomised controlled trials (RCTs) comparing groups with and without a weight-reducing diet can answer these issues, we only included RCTs in our systematic review. Thirty articles reporting on eight studies met the inclusion criteria. The 8 included studies involved a total of 2100 participants with high blood pressure and a mean age of 45 to 66 years. Mean treatment duration was 6 to 36 months, and there was little or no information about deaths or other long-term complications. Three of eight studies provided effects on systolic and diastolic blood pressure, suggesting that weight loss interventions reduced systolic and diastolic blood pressure by 4.5 mm Hg and 3.2 mm Hg, respectively. Five out of eight studies reported body weight; weight loss interventions reduced weight by 4.0 kg as compared to controls. No useful information on adverse effects was reported in the included trials.

In conclusion, we found no evidence for effects of weight loss diets on death or long-term complications and adverse events. Results on blood pressure and body weight should be considered uncertain, because not all studies were included in the analyses.

Authors' conclusions: 

In this update, the conclusions remain the same, as we found no new trials. In people with primary hypertension, weight loss diets reduced body weight and blood pressure, however the magnitude of the effects are uncertain due to the small number of participants and studies included in the analyses. Whether weight loss reduces mortality and morbidity is unknown. No useful information on adverse effects was reported in the relevant trials.

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Background: 

All major guidelines for antihypertensive therapy recommend weight loss. Thus dietary interventions that aim to reduce body weight might be a useful intervention to reduce blood pressure and adverse cardiovascular events associated with hypertension.

Objectives: 

Primary objectives

To assess the long-term effects of weight-reducing diets in people with hypertension on all-cause mortality, cardiovascular morbidity, and adverse events (including total serious adverse events, withdrawal due to adverse events, and total non-serious adverse events).

Secondary objectives

To assess the long-term effects of weight-reducing diets in people with hypertension on change from baseline in systolic blood pressure, change from baseline in diastolic blood pressure, and body weight reduction.

Search strategy: 

We obtained studies from computerised searches of the Cochrane Central Register of Controlled Trials (CENTRAL), the Cochrane Hypertension Specialised Register, Ovid MEDLINE, and Ovid EMBASE, and from searches in reference lists, systematic reviews, and the clinical trials registry ClinicalTrials.gov (status as of 2 February 2015).

Selection criteria: 

We included randomised controlled trials (RCTs) of at least 24 weeks' duration that compared weight-reducing dietary interventions to no dietary intervention in adults with primary hypertension.

Data collection and analysis: 

Two review authors independently assessed risk of bias and extracted data. We pooled studies using fixed-effect meta-analysis. In case of moderate or larger heterogeneity as measured by Higgins I2, we used a random-effects model.

Main results: 

This review update did not reveal any new studies, so the number of included studies remained the same: 8 studies involving a total of 2100 participants with high blood pressure and a mean age of 45 to 66 years. Mean treatment duration was 6 to 36 months. We judged the risk of bias as unclear or high for all but two trials. No study included mortality as a predefined outcome. One RCT evaluated the effects of dietary weight loss on a combined endpoint consisting of the necessity of reinstating antihypertensive therapy and severe cardiovascular complications. In this RCT, weight-reducing diet lowered the endpoint compared to no diet: hazard ratio 0.70 (95% confidence interval (CI), 0.57 to 0.87). None of the studies evaluated adverse events as designated in our protocol. There was low-quality evidence for a blood pressure reduction in participants assigned to weight loss diets as compared to controls: systolic blood pressure: mean difference (MD) -4.5 mm Hg (95% CI -7.2 to -1.8 mm Hg) (3 of 8 studies included in analysis), and diastolic blood pressure: MD -3.2 mm Hg (95% CI -4.8 to -1.5 mm Hg) (3 of  8  studies included in analysis). There was moderate-quality evidence for weight reduction in dietary weight loss groups as compared to controls: MD -4.0 kg (95% CI -4.8 to -3.2) (5 of 8 studies included in analysis). Two studies used withdrawal of antihypertensive medication as their primary outcome. Even though we did not consider this a relevant outcome for our review, the results of these studies strengthen the finding of reduction of blood pressure by dietary weight loss interventions.

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