TABLE 2.
Systematic review steps and examples from nutrition-related topics1
| Examples |
|||
|---|---|---|---|
| Systematic review step | Vitamin D and bone health (10) | Soy and health outcomes (12) | (n-3) Fatty acids and arrhythmogenic mechanisms (13) |
| Form multidisciplinary research team (in addition to systematic review methodologists and systematic review sponsors) | Domain experts in nutrition, endocrinology, pediatrics, and biochemistry | Domain experts in soy research and relevant health areas | Domain experts in (n-3) fatty acids research and cardiac electrogenesis and arrhythmia outcomes |
| Develop analytic framework | Related intakes, serum 25(OH)D, active form [1,25(OH)D] and bone health | Not available | Different for whole animal, intact animal isolated organ and cell, and cell culture studies |
| Develop and refine key questions | Serum 25(OH)D and bone health | Soy formulations, doses, and purposes in trials | Evidence from whole animal studies that (n-3) fatty acids affect arrhythmogenic outcomes |
| Intake or sun exposures and serum 25(OH)D | Whole soy or soy constituents and heath outcomes | ||
| Vitamin D intakes and BMD, fractures, or falls; variation with age, ethnicity, geography, BMI | Dose-response of soy forms or constitutions | Evidence from cell culture and tissue studies that (n-3) fatty acids directly affect cell organelles involved in electrogenesis | |
| Sunlight and 25(OH)D without ↑ skin cancer | Frequency and type of adverse effects | ||
| Intakes related to toxicities | Dose-response of whole soy and constituents on safety | ||
| Define eligibility criteria | Some questions limited to RCT | Inclusions: subjects ≥13 y; RCT, cohorts, cross-over and nonrandomized comparison studies; ≥5 subjectsin soy arm; any health condition; quantification of soy intake; outcomes of interest; ≥4-wk duration | Inclusions: experiments of (n-3) fatty acids and arrhythmia, intermediate mechanisms of arrhythmia, and electrogenesis |
| Some questions included prospective cohorts, case-control, and before-after studies. | |||
| One question restricted to existing systematic reviews | Exclusions: letters or abstracts; mechanisms related to eicosanoids, enzymes, receptors, membrane composition, fluidity, or phospholipids; nonmammalian animals or cell lines; no relevant outcomes; no (n-3) fatty acids intervention; reviews; safety assessments | ||
| Included studies that assessed vitamin ergocalciferol or cholecalciferol with or without calcium supplementation | |||
| Excluded studies that used calcium with vitamin D as a control arm unless a placebo was available as a comparator; vitamin D preparations calcitriol or alphacalcidol; studies on the efficacy of vitamin D for the treatment of secondary causes of osteoporosis or for treatment of vitamin D-dependent rickets | Exclusions: soy mixed with other ingredients; soy enteral feedings; reviews; nontrial observational studies; animal or in vitro studies; ingested soy not quantified; insignificant amounts of soy; no intake data | ||
| Identify search terms and strategy | 130 key terms | 33–63 key terms per search | 64 search terms |
| Screen abstracts according to eligibility criteria | 6566 unique records | ∼4800 abstracts | 1807 abstracts |
| Articles retrieved for evaluation | 1447 reports | 599 full text articles | 274 articles |
| Extract data from articles which met inclusion criteria | 167 articles | 178 articles | 89 articles |
| Construct evidence and summary tables | 18 summary tables | 86 summary tables | 31 summary tables |
| Assess methodological quality, applicability | Jadad scale for RCT | 3 categories (A,B,C) of methodological quality | 4 categories for fatty acid and/or level of fat in the comparison diet |
| Good, fair, or consistent rating for observational studies | 3-category applicability grade | ||
| Perform meta-analyses, as appropriate | Meta-analysis of RCT that assessed interventions, populations, and outcomes | Meta-analysis for several cardiovascular outcomes | Meta-analyses for whole animal studies |
| Meta-regression of differences across studies and dose-responses | For isolated organ and cell studies, qualitative data summary | ||
| Synthesize results, write report, have report reviewed | Report written by EPC; peer review by TEP members and external reviewers | Report written by EPC; peer review by TEP members and external reviewers | Report written by EPC; peer review by TEP members and external reviewers |
1
EPC, evidence-based practice center; FA, fatty acid; RCT, randomized controlled trial; TEP, technical expert panel; 25(OH)D, 25-hydroxyvitamin D; 1,25(OH)D, 1,25-dihydroxyvitamin D.