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Screening for lipid disorders: diet and exercise therapy |
Pignone M P, Philips C J, Lannon C M, Mulrow C D, Teutsch S M, Lohr K N, Whitener B L |
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Authors' objectives This review addresses key question 2 of the report: diet and exercise therapy for lipid disorders. Systematic reviews pertaining to questions 1 (drug therapy for lipid disorders) and 3 (screening strategies for lipid disorders) are summarised in other DARE abstracts.
The aim was to assess the effects of diet and exercise therapy, compared with no treatment, on improving outcomes in patients with 'abnormal' lipid levels, but no known coronary heart disease (CHD), i.e. people similar to those who would be identified by screening. The objective was addressed by focusing on four supplementary questions.
What is the effect of dietary counselling in primary care settings on cholesterol levels?
What is the effect of dietary counselling on CHD rates?
Does knowledge of one's cholesterol level increase the effectiveness of dietary therapy for lipid disorders?
What is the effect of exercise advice on cholesterol levels and CHD events?
The authors focused on the population of the USA.
Searching MEDLINE (from 1995 to June 1999) and the Cochrane Controlled Trials Register were searched; the search terms were given. Also searched were the U.S. Preventive Services Task Force (USPSTF) Guide to clinical preventative services (see Other Publications of Related Interest), systematic reviews, meta-analyses and evidence-based practice guidelines on the treatment of lipid disorders. The bibliographies of included articles were also handsearched. Adverse effects were searched for using the terms 'cholesterol', 'cholesterol dietary', 'hypercholesterolemia' and the exploded term 'anticholesteremic agents (adverse effects)'.
Study selection Study designs of evaluations included in the reviewThe pre-specified criteria were randomised controlled trials (RCTs) with a study duration of at least 1 year. The authors also summarised and included data from published meta-analyses.
Specific interventions included in the reviewNo set inclusion criteria were described. The authors stated they were interested in diet and exercise therapy on patients with lipid disorders, which they defined as 'general dietary counselling for freeliving patients conducted by a health care provider (physician, nurse, dietician)'. The search strategy stipulated 'diet', 'diet therapy' and 'dietary advice'. In the report, the included interventions were: dietary advice; multiple risk factor interventions (e.g. smoking cessation, diet and exercise interventions in combination); the impact of learning one's cholesterol level; dietary interventions for children (e.g. changes in school-based diet, counselling and tuition in the use of food diaries). Three interventions were excluded: mass media interventions, changes in legislation and dietary supplement interventions.
Participants included in the reviewThe authors pre-specified only ambulatory patients as their inclusion criterion. Participants were excluded if they were institutionalised, metabolic ward patients, or inpatients. The participants actually included were varied and were taken from diverse age groups, including children as young as 18 months to those aged over 70 years. The settings were also varied: primary care, school, workplace and family setting.
Outcomes assessed in the reviewThe included studies had to address the following outcomes: total mortality, CHD mortality, CHD events, the need for CHD procedures, the percentage change in total cholesterol from baseline to after treatment, and adverse events. In addition, the authors reported the effects of interventions on various growth and development markers for children in some studies, and the contents of lunch boxes and the participants' knowledge of diet and lowering of lipid intake.
How were decisions on the relevance of primary studies made?Two people independently reviewed the titles and abstracts of the articles identified by the literature searches, and excluded those that did not meet the criteria. Any disagreements were resolved by reading the full text of the article and discussion with a third reviewer until a consensus was agreed.
Assessment of study quality The quality of the studies was assessed using four criteria: adequate inclusion criteria, adequate randomisation and concealment, non-differential loss to follow-up and the use of intention-to-treat analysis. The criteria were used following reference to the USPSTF Guide (see Other Publications of Related Interest). The external validity of the studies was assessed by reference to the race and gender of the participants. Two people assessed the quality of the RCTs found.
Data extraction The authors stated that they abstracted data using tables in MS Word and MS Excel computer programs. The authors did not state how many reviewers performed the data extraction.
The data were extracted on an intention-to-treat basis. The categories of data extracted were: study design and characteristics, participant characteristics, details of specific interventions, effects on blood lipid concentration, main outcomes including relative risk (mortality and cardiovascular events), quality of the studies and adverse effects. Further details were given in the report.
Methods of synthesis How were the studies combined?Information from studies and meta-analyses were combined in a narrative synthesis. The data were presented in tabular format, and described and discussed under the following subject headings: effectiveness of dietary advice in primary care settings; effectiveness of dietary advice in large multi-risk factor trials; impact of learning one's cholesterol level on the effectiveness of diet therapy; diet therapy (subdivisions: children and adolescents; infants and toddlers; school health interventions); and harms of dietary interventions in children and adolescents (exercise and lipids).
How were differences between studies investigated?An assessment of heterogeneity was not described. However, the different studies were described in detail with the aid of subheadings and tables.
Results of the review Nineteen studies with 103,020 participants were identified: 18 RCTs and 1 quasi-randomised trial. The studies were divided into the following categories: effectiveness of dietary advice in primary care settings (6 studies; n=12,042); effectiveness of dietary advice in large multi-risk factor trials (5 studies; n=81,736); impact of learning one's cholesterol level on the effectiveness of diet therapy (4 studies; n=2,069); diet therapy in children and adolescents, infants and toddlers (4 studies; n=7,173).
The authors stated 'Intensive, individualised diet therapy such as that offered in MRFIT, appears to be relatively ineffective as a means of reducing lipid abnormalities and CHD events when compared with the secular trend toward declining average cholesterol levels that may be an effect of population-level interventions'.
Knowledge of one's cholesterol level did not appear to affect the overall impact of dietary therapy, although persons with elevated cholesterol may be slightly more able to reduce their total cholesterol.
Intensive educational interventions aimed at decreasing dietary saturated fat and cholesterol and serum cholesterol levels in children had modest effects on the adoption of a low-fat diet by children and their families. Such interventions had a very modest, if any, effect on lowering serum cholesterol. Moreover they may be associated with harms specific to children.
Exercise interventions considered as a whole did not appear to have a large impact on lipid levels. However, some studies employing rigorous activity prescriptions and producing weight loss showed changes in lipid profiles that may be clinically meaningful. It was noted that these programmes have been difficult to implement widely.
Authors' conclusions Diet therapies reduced CHD events in secondary prevention settings. Low-fat diets reduced CHD events in institutionalised patients without CHD, but not in freeliving low-risk populations, apart from in the Oslo trial. Intensive interventions achieved modest long-term reductions in total cholesterol. In primary prevention, small reductions in cholesterol may be explained by incomplete adherence.
Knowledge of one's cholesterol level did not appear to affect the outcomes of diet therapy. Intensive educational interventions to reduce dietary saturated fat and cholesterol and serum cholesterol in children had modest effects on the take-up of low-fat diet by children and their families, and very modest, if any, effects on lowering serum cholesterol. Such interventions may be associated with harms specific to children.
CRD commentary The review question was appropriate and focused on the effects of interventions to reduce lipid levels in those with abnormally high lipid levels. The authors used a systematic approach and added information from observational studies and published meta-analyses when their searches did not identify any controlled studies for inclusion. Although the review stated that exercise interventions would be included, this was not stated as an inclusion criterion. Specific terms for exercise interventions were not included in the search strategy and important studies might, therefore, have been missed.
The search strategy was adequate, although some useful trials might have been missed since the search was restricted to English publications found on two electronic databases. The validity of the trials was assessed using published methods, which were implemented well. However, there was no description of the quality of evidence from different study designs, i.e. meta-analyses, RCTs and observational studies. Evidence from the better quality trials was not highlighted.
Details of the primary data were given and appropriate information was tabulated. The narrative synthesis, which was split into useful sections, was also appropriate. Harms, adverse events and exercise interventions were described from observational studies, experimental design studies and meta-analyses, which provided only a brief description of the data. The authors' conclusions seem to follow from the results presented.
Implications of the review for practice and research Practice: The authors did not state any implications for practice.
Research: The authors stated that the effectiveness of novel methods of diet therapy, including 'Mediterranean' diets, should be examined in primary prevention populations.
Funding Agency for Healthcare Research and Quality, contract number 290- 97-0011.
Bibliographic details Pignone M P, Philips C J, Lannon C M, Mulrow C D, Teutsch S M, Lohr K N, Whitener B L. Screening for lipid disorders: diet and exercise therapy. Rockville, MD, USA: Agency for Healthcare Research and Quality. Systematic Evidence Review; 4. 2001 Other publications of related interest U.S. Preventive Services Task Force. Guide to clinical preventive services. 2nd ed. Alexandria (VA): International Medical Publishing; 1996.
Indexing Status Subject indexing assigned by CRD MeSH Coronary Disease; Hyperlipidemias /epidemiology /prevention & Mass Screening /methods; control AccessionNumber 12002008769 Date bibliographic record published 28/02/2005 Date abstract record published 28/02/2005 Record Status This is a critical abstract of a systematic review that meets the criteria for inclusion on DARE. Each critical abstract contains a brief summary of the review methods, results and conclusions followed by a detailed critical assessment on the reliability of the review and the conclusions drawn. |
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