Review: Dietary advice modestly reduces blood pressure, serum cholesterol, and urinary sodium levels
ACP J Club. 1998 Mar-April; 128:37. doi:10.7326/ACPJC-1998-128-2-037
Brunner E, White I, Thorogood M, et al. Can dietary interventions change diet and cardiovascular risk factors? A meta-analysis of randomized controlled trials. Am J Public Health. 1997 Sep;87:1415-22.
To determine the effectiveness, using meta-analysis, of dietary advice on modifying risk factors for chronic disease defined as cardiovascular disease or breast cancer.
Studies were identified by computer and manual searches of databases, journals, and lists of conference abstracts published as of 1993.
Randomized controlled trials of free-living adults that lasted ≥ 3 months were selected if the trial involved primary prevention (< 25% of participants were being treated for a diagnosed disease before entry into the trial) and the intervention group was provided advice to change dietary fat, sodium, or fiber intake. Trials were excluded if the intervention and control groups differed more than by dietary intervention, whether supplements or provided meals were used, or whether they involved multiple interventions or a crossover design.
Data were extracted on patient characteristics and numbers, nature of intervention, study location, dietary goals, blood pressure, levels of total serum cholesterol and urinary sodium, and dietary fat.
17 trials that included 6893 participants (estimated 51% women), with 3736 (54%) in the intervention groups, were identified. 3817 (55%) participants were randomly assigned individually and 3076 (45%) by workplace. Dietary advice reduced systolic blood pressure by an average of 1.3 mm Hg (95% CI 0.3 to 2.4 mm Hg, P = 0.01) in 8 trials 3 to 6 months in duration and by 1.9 mm Hg (CI 0.8 to 3.0 mm Hg, P < 0.001) in 5 trials 9 to 18 months in duration; it reduced diastolic blood pressure by 0.7 mm Hg (CI 0.0 to 1.5 mm Hg, P = 0.06) in 8 trials 3 to 6 months in duration, with a trend toward reduction (1.2 mm Hg reduction, CI -0.2 to 2.6 mm Hg, P = 0.09) in 5 trials 9 to 18 months in duration. Dietary advice reduced total serum cholesterol levels by 0.28 mmol/L (CI 0.15 to 0.42 mmol/L) in 8 trials 3 to 6 months in duration and by 0.22 mmol/L (CI 0.05 to 0.39 mmol/L) in 5 trials 9 to 18 months in duration. Dietary advice reduced 24-hour urinary sodium levels by 45 mmol (CI 32.8 to 57.1 mmol) in 3 trials 9 to 18 months in duration. Dietary advice decreased dietary fat as a percentage of total calories by 2.5% (CI 1.1% to 3.9%) for 4 trials 3 to 6 months in duration when the trials of breast cancer were excluded. Trials of breast cancer showed larger decreases in dietary fat as percentage of total calories.
Dietary advice as a primary preventive therapy modestly reduces dietary sodium and fat levels and lowers systolic and diastolic blood pressure and total serum cholesterol levels.
Sources of funding: Health Education Authority and the North Thames (West) Regional Health Authority.
For article reprint: Dr. E. Brunner, Department of Epidemiology and Public Health, University College London, 1-19 Torrington Place, London WC1E 6BT, England, UK. FAX 44-171-380-7920.
The characteristics of study participants may be particularly relevant during evaluation of whether study findings apply to other populations. Many studies examining the effects of dietary salt on blood pressure and fat consumption on serum lipid levels have been done in controlled settings, such as in metabolic wards or among out-patient volunteers who had meals provided. To better estimate the population effects of reducing salt and fat consumption on cardiovascular disease risk factors, Brunner and colleagues examined the results of clinical trials that enrolled only free-living participants. Pooled data from 17 studies revealed that advice on limiting dietary salt intake (confirmed by urinary sodium excretion) and fat consumption (estimated from dietary questionnaires) resulted in modestly lower blood pressure and total serum cholesterol levels.
These results are probably more generalizable than studies done in metabolic ward settings; however, they may still overestimate the public health effect of the interventions. Volunteers in clinical studies differ from nonvolunteers (e.g., volunteers are more likely to comply with the study protocol) (1). Although dietary counseling interventions may be effective, they also need to be practical; some studies included as many as 10 to 32 follow-up contacts. Further, the effects of dietary interventions tend to attenuate after counseling is discontinued. Finally, although it is reasonable to extrapolate that reductions in cardiovascular disease mortality result from changes in risk factors, such as lowering of blood pressure and total serum cholesterol levels, the magnitude of such reductions is uncertain. The results of Brunner and colleagues' study indicate that brief counseling of healthy adults may be worthwhile during primary care encounters. However, the combination of targeted counseling with innovative population-based strategies may prove to be a more cost-effective approach to lowering dietary salt and fat consumption and, in turn, cardiovascular disease mortality.
Joel A. Simon, MD, MPH
San Francisco Veterans Affairs Medical CenterUniversity of California, San FranciscoSan Francisco, California, USA
Joel A. Simon, MD, MPH
San Francisco Veterans Affairs Medical CenterUniversity of California, San Francisco
San Francisco, California, USA