Effect of iron intake on iron status: a systematic review and meta-analysis of randomized controlled trials.
Study Goal
The researchers aimed to assess how baseline iron status, sex, menopausal status, intervention duration, iron form, and daily dose influence changes in iron status biomarkers in response to iron supplementation.
Results Summary
Iron supplementation significantly improved iron status, with study duration and dose affecting serum ferritin levels and baseline iron status influencing hemoglobin concentrations. However, high heterogeneity and insufficient data on body iron, sex, or menopausal status limited comprehensive conclusions.
Population
Participants in randomized controlled trials (RCTs) of iron supplementation and fortification, though specific demographics (e.g., age, health status) are not detailed.
Effective Dosage
Not specified (study analyzed effects per gram of iron but did not list exact dosages).
Duration
Varied by study (duration was a variable analyzed but not uniformly reported).
Interactions
None mentioned
| Intervention | Direction | Endpoint | Population | Dosage | Impact | Claim # |
|---|---|---|---|---|---|---|
iron supplementation | increase | iron status | - | - | significantly improved | #1 |
iron supplementation | increase | serum ferritin (SF) | - | 0.51 μg/L | increase in SF concentration/wk | #2 |
iron supplementation | increase | serum ferritin (SF) | - | 0.10 μg/L | increase in SF concentration/g Fe | #3 |
iron supplementation | decrease | hemoglobin concentrations | - | -0.08 g/dL | -0.08 g/dL per 10-μg/L increase in baseline SF concentration | #4 |
BACKGROUND: The response of status biomarkers to an increase in iron supply depends on several physiologic and environmental factors, which make it difficult to predict the outcome of an intervention. OBJECTIVE: We assessed effects of baseline iron status, sex, menopausal status, duration of intervention, iron form, and daily dose on the change in iron status in response to iron supplementation. DESIGN: A systematic review of randomized controlled trials (RCTs) of iron-supplementation and -fortification trials that assessed effects on hemoglobin, serum ferritin (SF), soluble transferrin receptor, or body iron was conducted. Subgrouping and straight-line and curved metaregression were used to describe the magnitude and dose-responsiveness of effect modifiers with respect to changes in status. RESULTS: Forty-one RCTs were included; none of the RCTs were judged at low risk of bias. Random-effects meta-analyses showed that iron supplementation significantly improved iron status but with high levels of heterogeneity. Metaregression explained approximately one-quarter of between-study variance in effect size. There were clear effects on SF with study duration (increase in SF concentration/wk: 0.51 μg/L; 95% CI: 0.02, 1.00 μg/L; P = 0.04) and dose (increase in SF concentration/g Fe: 0.10 μg/L; 95% CI: 0.01, 0.20 μg/L; P = 0.036) and on hemoglobin concentrations with baseline iron status [-0.08 g/dL (95% CI: 0.15, 0.00 g/dL) per 10-μg/L increase in baseline SF concentration; P = 0.02]. Insufficient data were available to assess effects on body iron, sex, or menopausal status. CONCLUSION: Quantitative relations between baseline iron status, study duration, and iron dose on changes in iron-status biomarkers, which were generated from the meta-analyses, can be used to predict effects of trials of iron supplementation and fortification and to design iron-intervention programs.