IJE Advance Access originally published online on March 31, 2006
International Journal of Epidemiology 2006 35(3):538-540; doi:10.1093/ije/dyl060
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Cochrane Column |
Cochrane Column
South African Cochrane Centre, Medical Research Council, PO Box 19070, Tygerberg 7505, South Africa. E-mail: taryn.young{at}mrc.ac.za
This month the focus is on the Cochrane Review by Brunner et al., which assessed the effects of providing dietary advice to achieve sustained dietary changes or improved cardiovascular risk profile among healthy adults.
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The aim of the Column is to highlight Cochrane systematic reviews of relevance to public health and to stimulate debate on relevance, feasibility, and acceptability. The Cochrane Collaboration (http://www.cochrane.org) is an international, non-profit organization that prepares and disseminates up-to-date systematic reviews on the effects of healthcare interventions in order to help people make well-informed decisions. Systematic reviews aim to answer focused healthcare questions by systematically identifying and evaluating all relevant research studies and synthesizing their results.
If you are interested in contributing to the Cochrane Column or The Cochrane Collaboration, contact me at the South African Cochrane Centre.
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A summary of Cochrane reviews (and protocols) of relevance to health promotion and public health can be viewed on the Cochrane Health Promotion and Public Health website: http://www.vichealth.vic.gov.au/cochrane/
Dietary advice for reducing cardiovascular risk: Cochrane systematic review
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Background |
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 Top Background MethodologyResultsDiscussion and conclusionsReferences |
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Drug treatment may be appropriate among individuals at high risk of cardiovascular disease (CVD); however, in order to prevent or delay the onset of disease in the general population, and thus reduce the burden on health services, adoption of a healthy diet is preferable to long-term medication. Dietary advice can take many forms: verbal or written, single or multiple contacts with individuals or groups, and may be delivered in primary health care and other settings such as community centres or workplaces. This review assessed the effects of providing dietary advice to achieve sustained dietary changes or improved cardiovascular risk profile among healthy adults.
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Methodology |
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TopBackgroundMethodologyResultsDiscussion and conclusionsReferences |
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Trials were identified from the Cochrane Controlled Trials Register, MEDLINE, EMBASE, DARE, CAB Health, dissertation abstracts, and reference lists of articles. Researchers in the field were contacted. Randomized studies with no more than 20% loss to follow-up, lasting at least 3 months, and involving healthy adults that compared dietary advice with no advice or less intensive advice were included. Trials involving children, trials to reduce weight, and those involving supplementation were excluded. Two authors independently screened titles, abstracts, and methods sections, and extracted data. Outcome measures consisted of self-report dietary measures, biomarkers, and diet-related CVD risk factors. Subgroup analyses examined the effects of gender, disease risk, intervention setting, intervention intensity, and trial duration.
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Results |
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TopBackgroundMethodologyResultsDiscussion and conclusionsReferences |
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Twenty-three trials with a total of 24 443 participants were included in the review. Six trials utilized a cluster design and the units of randomization (individually randomized participants and clusters) totalled 11 723. The modal duration of follow-up was 6 months. There were four short duration trials of 3 or 4 months. Nine studies contributed results for 12–48 months of follow-up.
Dietary advice reduced total serum cholesterol by 0.13 mmol/l (95% confidence interval 0.03–0.23) and LDL cholesterol by 0.13 mmol/l (0.01–0.25) after 3–12 months. Mean HDL cholesterol levels were unchanged. Dietary advice reduced blood pressure by 2.10 mm Hg systolic (1.37–2.83), 1.63 mm Hg diastolic (0.56–2.71) and 24 h urinary sodium excretion by 44.2 mmol (33.6–54.7). Self-reported dietary intake may be subject to reporting bias, and there was significant heterogeneity in all the following analyses. Compared with no advice, dietary advice increased fruit and vegetable intake by 1.24 servings/day (0.43–2.05). Trials of advice to increase fruit and vegetable consumption (Figure 1) suggest that interventions by health professionals are particularly effective. Dietary fibre intake increased with advice by 7.22 g/day (2.84–11.60), while total dietary fat as a percentage of total energy intake fell by 6.18% (4.00–8.36) with dietary advice and saturated fat intake fell by 3.28% (1.92–4.64).
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Discussion and conclusions |
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TopBackgroundMethodologyResultsDiscussion and conclusionsReferences |
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Dietary advice appears to be effective in bringing about modest beneficial changes in diet and cardiovascular risk factors over
9 months but longer-term effects are not known. Interventions by health professionals to increase fruit and vegetable consumption were particularly effective. Other subgroup comparisons such as that for dietary fat reduction do not support this interpretation. The healthcare-based trials in Figure 1 involve healthy but highly motivated participants with mammographic dyplasia or colorectal adenomas. The small increase in fruit and vegetable consumption (0.41 servings/day) obtained in non-healthcare settings indicates that valuable change can be achieved among healthy but relatively unmotivated adults. Our evidence suggests that resource-intensive interventions involving detailed dietary advice given by health professionals are appropriate for high-risk individuals. A low-cost intervention reaching a large proportion of the healthy population is probably more cost effective than a slightly more effective high-intensity intervention requiring health professionals to deliver it. The full text of the review is available in The Cochrane Library: Brunner EJ, Thorogood M, Rees K, Hewitt G. Dietary advice for reducing cardiovascular risk. The Cochrane Database of Systematic Reviews 2005, Issue 4. Art. No.: CD002128 [GenBank] .pub2. DOI: 10.1002/14651858.CD002128.pub2.
Commentary: Dietary advice for reducing cardiovascular risk
1 Chair in Public Health, Deakin University, Australia
2 Co-Director, Cochrane Collaboration Health Promotion and Public Health Field
The impact of providing dietary advice to adults is a significant public health evidence quest. Should this approach be effective, not only can it make a significant impact at the population level on a range of health outcomes of the adult population, but owing to the role that adult health plays in the context of familial settings, the potential impact on a range of nutritionally determined outcomes for children, most notably overweight and obesity, would be substantive. There is ample evidence that parental patterns of eating as well as the health status of parents influences child health outcomes.1
This review and its contributing studies have a number of particular strengths but also a number of limitations and research recommendations that researchers and policy makers need to be mindful of. In their favour, the primary studies and the review itself are not restricted to the higher sociodemographic groups, for which you might expect a stronger effect size, but the total number of 24 443 participants in the review comprises 47% from the working class, low income, welfare, or blue collar backgrounds. Even though a moderate impact was observed, the length of most interventions was <12 months, and disappointingly, four were 3–4 months duration. Previous reviews have demonstrated that it is not unusual for interventions to demonstrate effect in a short-term time period of 3 months, but not over an extended period, and so the lack of follow-up date for these studies mediates their potential effectiveness.2 However, the fact that most interventions were <12 months plus that a large proportion of participants were relatively socially worse off than in many trial contexts, adds weight to the support for dietary advice given through a range of modes, as an essential evidence-based strategy for the improvement of health outcomes. The increased impact by interventions delivered within the health service sector is an important learning from this review. All systematic reviews, and specifically the primary studies contributing to systematic reviews, would benefit by including and reporting on additional dimensions, which are essential for policy-focused users of reviews and those in countries who are not represented in the primary study geographic mix, such as stronger contextual understanding, economic evaluations, analysis of the differential impact of the intervention on health inequalities, and process data (the extent to which the intervention was received as intended).3
Finally, the recommended opportunities for research are reflected in the review; however, additionally, integrated interventions that focus on outcomes for other members of the family would be a novel intervention model to tackle, thus, providing a strong evidence base for the public health benefits of targeting parents and adults as a way of achieving integrated lifecourse outcomes for the population.
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References |
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TopBackgroundMethodologyResultsDiscussion and conclusionsReferences |
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1 Waters E, Baur L. Childhood obesity—modernity's scourge. Med J Aust 2003;178:422–23.[Medline]
2 Glenny A, O'Meara S, Melville A, Sheldon TA, Wilson C. The treatment and prevention of obesity: a systematic review of the literature. Int J Obes 1997;21:715–37.[CrossRef][Web of Science][Medline]
3 Jackson N, Waters E, for the Guidelines for Systematic Reviews in Health Promotion and Public Health Taskforce. Criteria for the systematic review of health promotion and public health interventions. Health Promot Int 2005;20:367–74.
Commentary: Dietary advice for reducing cardiovascular risk
Food and Nutrition Group, School of Health and Social Care, University of Teesside, UK
We welcome the publication of this Cochrane systematic review as it draws attention to an important area in the public health domain. All public health practitioners should be aware of this highly relevant and comprehensive review. When used as a reference tool, either for research or practice, the summary data provided by Cochrane Reviews are second to none.
This review on the subject of the reduction of cardiovascular risk has excellent methodology (as is typical of a Cochrane Systematic Review) and the authors have a widespread knowledge of the field, which helps when setting the results in the context of current understanding.
Although the mean change in the risk factors of individuals was reported as being small, as the authors suggested when combined they may lead to greater gain than originally thought. As the trials assessed were carried out in workplaces and communities, as opposed to studies in metabolic wards, the applicability of the evidence generated from the general population is good. However, the majority of the trials were located in the United States of America, which raises the question of how well the evidence garnered from these populations will transfer to other populations that differ significantly.
The area of dietary health promotion at both the population and individual level is currently an extremely hot topic and a review being published on this topic is very welcome.
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