Daily iron supplementation for improving iron status and health among menstruating women

  • Protocol
  • Intervention

Authors

  • Sant-Rayn S Pasricha,

    1. World Health Organization, Micronutrients Unit, Department of Nutrition for Health and Development, Geneva, Geneva, Switzerland
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  • Luz Maria De-Regil

    Corresponding author
    1. World Health Organization, Evidence and Programme Guidance, Department of Nutrition for Health and Development, Geneva, Switzerland
    • Luz Maria De-Regil, Evidence and Programme Guidance, Department of Nutrition for Health and Development, World Health Organization, 20 Avenue Appia, Geneva, 1211, Switzerland. deregillu@who.int.

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Abstract

This is the protocol for a review and there is no abstract. The objectives are as follows:

To establish the effects of daily supplementation with iron, alone or in combination with folic acid or vitamin C, on anaemia and iron status, as well as on physical, psychological and neurocognitive health, among menstruating women.

Background

Description of the condition

Over 1.6 billion people worldwide have anaemia, a condition in which haemoglobin production is diminished. Women of menstruating age account for approximately a third of all cases of anaemia worldwide, and approximately 468 million, or 30%, of all women aged 15 to 49 years are anaemic (WHO/CDC 2008). Iron deficiency (ID) is believed to contribute to at least half the worldwide burden of anaemia, especially in non-malaria-endemic countries (Stoltzfus 2001). Iron deficiency is thus considered the most prevalent nutritional deficiency in the world.

Iron deficiency occurs following negative iron balance. As body iron stores are exhausted, the production of red blood cells is impaired, and finally, iron deficiency anaemia (IDA) results (Suominen 1998). The major causes of negative iron balance include inadequate dietary iron intake (due to consumption of a diet with a low overall or bioavailable iron content); increased losses of iron due to chronic blood loss occasioned by intestinal hookworm infestations, which are endemic in many countries (Hotez 2005), and increased iron requirements (for example, during growth or pregnancy). Low dietary iron intake and bioavailability are considered key contributors to the burden of iron deficiency. This is especially so in populations consuming diets that are low in meat sources and high in cereals such as wheat, rice, maize and millet, which are rich in phytates, a type of compounds that bind to iron in the meal and prevent its absorption (Sharpe 1950). Other dietary components such as tannins (found in tea) and calcium (contained in milk products) also inhibit iron absorption.

Women beyond menarche and prior to menopause are at especially high risk of iron deficiency due to menstrual blood losses. The onset of menstrual blood losses accompanied by rapid growth, with an associated expansion of red cell mass and tissue iron requirements, means adolescent girls have a particularly high iron need compared with their male counterparts, and as this is compounded by inadequate dietary iron intake, these girls may be at especially high risk of iron deficiency (Dallman 1992). Other important causes of iron deficiency in women include intestinal malabsorptive conditions such as coeliac disease, chronic blood losses due to menorrhagia from uterine pathologies (such as fibroids), frequent blood donation and benign and malignant gastrointestinal lesions (Goddard 2011). Iron deficiency, with and without anaemia, has also been noted to be prevalent among female athletes and is thought to be due to diets deficient in iron, increased losses due to gastrointestinal tract bleeding and reduced iron absorption due to subclinical inflammation (Peeling 2008).

As well as being critical to the production of haemoglobin, iron has a critical role in many other aspects of human physiology as it is involved in a range of oxidation-reduction enzymatic reactions in the muscle and nervous tissue (Andrews 1999), as well as other organs. Iron deficiency and iron deficiency anaemia have been associated with a range of adverse physical, psychological and cognitive effects. On the one hand, animal models suggest a role for iron in brain development and function, with iron depletion being associated with dysregulated neurotransmitter levels (Lozoff 2007), and some, but not all, clinical studies have shown associations between iron supplementation and improvement in cognitive performance (Murray-Kolb 2007), mood and well being, with a reduction in fatigue (Verdon 2003). On the other hand, observational studies have suggested that iron deficiency in the absence of anaemia impairs exercise performance in women (Scholz 1997), while some, but not all, interventional studies of iron supplementation among the same population have shown variable improvements in maximal and submaximal exercise performance (LaManca 1993; Brownlie 2002), endurance (Hinton 2000; Brownlie 2004) and muscle fatigue (Brutsaert 2003). Observational and interventional studies have also suggested associations between iron status and haemoglobin concentrations and work productivity (Wolgemuth 1982; Li 1994: Scholz 1997). When anaemia is severe, it may cause lethargy, fatigue, irritability, pallor, breathlessness and reduced tolerance for exertion.

Alleviation of iron deficiency anaemia among menstruating women is thus considered a major public health priority, both to improve their existing health status and to enhance their health in preparation for future pregnancies (WHO 2009).

Other causes of anaemia important to distinguish from iron deficiency include anaemia of chronic disease (associated with inflammation which causes iron to be withheld from erythropoiesis (the process by which red blood cells are produced)), functional iron deficiency (associated with renal impairment), genetic conditions of the red cell (haemoglobin, enzymes and membrane) and infectious diseases (including malaria).

Description of the intervention

Strategies to improve iron intake and alleviate IDA include mass and point-of-use fortification of foods with iron, dietary diversification to increase iron intake, absorption and utilisation, iron supplementation and antihelminthic treatment. Supplementation is probably the most widespread intervention practiced clinically and in public health.

Oral iron supplementation, administered once a day or more frequently, is the standard clinical practice of many physicians in the treatment of iron deficiency in women (Goddard 2011). Daily iron and folic acid supplementation for three months has also been widely recommended for the prophylaxis of iron deficiency in populations where the prevalence of anaemia exceeds 40% (WHO/UNICEF/UNU 2001). In addition to its haematological effects, the use of folic acid during the periconceptional period helps prevent babies being born with neural tube defects (WHO/UNICEF/UNU 2001).

Iron is generally administered as a salt compound in a tablet, capsule, liquid or dispersible formulation. The most commonly prescribed salts include ferrous sulphate, fumarate and gluconate (Pasricha 2010). Commonly reported side effects of iron supplements include gastrointestinal disturbances (especially constipation and nausea) and dark stools. In those using liquid formulations, tooth staining can occur. Slow or sustained release formulations, in which iron is surrounded by a coating, aim to alleviate gastrointestinal side effects by delaying delivery of iron to a more distal point in the gastrointestinal tract, but their efficacy has been questioned.

How the intervention might work

Iron is absorbed by intestinal cell luminal and basal transporters, transported bound to proteins to the bone marrow, muscle and other tissue, where it is taken up by specific receptors and used for biologic functions or stored (Andrews 1999). Textbooks advise that in an iron deficient anaemic individual, haemoglobin concentrations should rise by 1g/dL per week, with early evidence of red blood cell formation discernible in the peripheral blood after 72 hours of supplementation (Mahoney 2011).

There is an inverse relationship between iron status and the ability to absorb iron. Iron deficiency induces changes in intestinal iron transport that can double absorption of iron from the diet (Thankachan 2008). Thus, as with dietary sources of iron, absorption from supplements depends on the baseline iron status of the individual and the co-consumption of iron absorption enhancers (such as vitamin C, other acidic foods and meat) and inhibitors (calcium, phytates and tannins) (Hurrell 2010).

As mentioned above, the ubiquitous presence of iron in the human body is such that its deficiency impairs a number of physiological functions, and iron supplementation may thus benefit, physical, psychological and cognitive health. Improvements in haemoglobin and myoglobin concentrations may ensure adequate tissue oxygenation and performance (Umbreit 2005). Iron is also present in the brain in relatively large amounts and is involved in neurotransmitter function (Burhans 2005); an adequate supply may contribute to maintain a normal cognitive and psychological health, although the mechanisms are not completely elucidated as yet.

Despite the known and potential benefits of this intervention, it has been reported that daily iron supplementation in anaemic women increases their oxidative stress (King 2008; Tiwari 2011), although the clinical significance of this phenomenon in the short and long term remains unclear. Perhaps the most important side effect of iron supplements is the risk of severe toxicity of iron in overdose, albeit this is uncommon in women.

An additional consideration when providing supplements at population level is the endemicity of malaria in a given region. Approximately 40% of the world population is exposed to the malaria parasite and it is endemic in over 100 countries, causing more than a million deaths per year (WHO 2010). Provision of iron in malaria-endemic areas, particularly to children, has been controversial due to concerns that iron therapy may exacerbate infections, in particular malaria (Oppenheimer 2001; Okabe 2011), although it is still not completely clear whether iron produces the same effects among older populations or whether subclinical malaria alters the response to iron supplementation.

Why it is important to do this review

Daily oral supplementation in women has been a longstanding intervention both in the public health and clinical fields. Many patients and clinicians ascribe adverse health outcomes (including fatigue and lethargy, impaired cognitive performance and psychological dysfunction) to iron deficiency, even in the absence of anaemia, and attribute improvement in these symptoms to iron supplementation. In addition, many sporting authorities (including the International Olympic Committee (IOC 2009)) recommend screening of female athletes for iron deficiency in order to target iron supplementation, with a view to improving performance.

Several intervention trials have evaluated improvements in haemoglobin and iron status, as well as non-haematologic outcomes such as physical, cognitive and psychological health, in menstruating women receiving iron supplementation. However, evaluation of this intervention has not been subject to systematic review and it is thus difficult to estimate the benefits and risks associated with the daily use of iron supplements in menstruating women.

This review will complement the findings of other Cochrane systematic reviews assessing the use of iron supplements alone, or in combination with other vitamins and minerals, in different female populations: intermittent supplementation in children (De-Regil 2011), iron supplementation among children in malaria-endemic areas (Okabe 2011), intermittent iron supplementation in menstruating women (Fernandez-Gaxiola 2011), daily and intermittent iron and folic acid supplementation in pregnant women (Pena-Rosas 2009), multiple micronutrient supplementation in pregnancy (Haider 2006) and iron supplementation during the postpartum period (Dodd 2004).

Objectives

To establish the effects of daily supplementation with iron, alone or in combination with folic acid or vitamin C, on anaemia and iron status, as well as on physical, psychological and neurocognitive health, among menstruating women.

Methods

Criteria for considering studies for this review

Types of studies

Randomised and quasi-randomised controlled trials with either individual or cluster-randomisation. Quasi-randomised trials are trials that use systematic methods to allocate participants to treatment groups, such as alternation, assignment based on date of birth or case record number (Higgins 2011). We will include the first period of randomised cross-over trials.

We will not include observational study designs (for example, cohort or case-control studies) in the meta-analysis but we will consider such evidence in the discussion where relevant.

Types of participants

Inclusion Criteria:

  • Menstruating women, that is women beyond menarche and prior to menopause who are not pregnant or lactating or have any condition that impedes the presence of menstrual periods, regardless of their baseline iron status/anaemia status, ethnicity, country of residence or level of endurance.

  • We will include studies for which results for females between 12 and 50 years of age (plausible age range for menstruation) can be extracted separately, or in which more than half of the participants fulfil this criterion (sensitivity analyses will be performed if marginal decisions are made). If we find studies with populations consisting of both males and females, we will consider them as awaiting assessment until we can secure the female-only information.

Exclusion Criteria:

  • Studies targeting populations with conditions affecting iron metabolism, intestinal malabsorption conditions, ongoing excessive blood loss (including ongoing blood donations), inflammatory bowel disease, cancer, chronic congestive cardiac failure, chronic renal failure, chronic liver failure or chronic infectious disease.

  • Studies that are purely evaluating kinetics of erythropoiesis or pharmacology of iron supplements or absorption.

  • Studies in hospitalised or ill people.

Types of interventions

Oral iron supplementation, with iron alone or in combination with folic acid or vitamin C, given no less than five days a week, regardless of the dose and duration of the intervention.

We will include the following comparisons:

  1. Daily oral supplementation with iron alone or in combination with folic acid or vitamin C versus a placebo or no intervention.

  2. Daily oral supplementation with iron alone or in combination with folic acid or vitamin C versus the same nutrients without iron.

We will include an overall comparison combining comparisons 1 and 2 to assess the effects of daily oral supplementation with iron alone or in combination with folic acid or vitamin C versus receiving no supplemental iron.

In this review, "iron supplement" refers to compounds containing iron salts such as ferrous sulphate, ferrous fumarate, ferrous gluconate, carbonyl or colloidal iron. Iron may have been delivered as a tablet, capsule, dispersible tablet or liquid.

We will include (and note) studies in which iron supplements are given along with co-interventions such as other nutrients (for example, zinc, vitamin A), deworming, education or other approaches only if the co-interventions were the same in both the intervention and comparison groups. We will not include studies where additional haemopoietic agents have been administered, such as exogenous erythropoietin.

Interventions excluded from this review will include point-of-use fortification with micronutrient powders or lipid-based foods, mass fortification of staple foods such as wheat or maize flours or condiments, and intermittent iron supplementation, which are evaluated in previous or ongoing Cochrane reviews.

Types of outcome measures

Primary outcomes
  1. Anaemia (haemoglobin concentrations below a cut-off defined by trial authors).*

  2. Haemoglobin (g/L).*

  3. Iron deficiency (as measured by trial authors by using indicators of iron status, such as ferritin or transferrin).*

  4. Iron deficiency anaemia (defined by the presence of anaemia plus iron deficiency, diagnosed with an indicator of iron status selected by trialists).*

  5. All-cause mortality.*

  6. Adverse side effects (as measured by trial authors: any adverse effects, abdominal pain, vomiting, nausea, heartburn, diarrhoea, constipation).*

  7. Cognitive function (as defined by trial authors, for example, for adolescents: school grades, test performance, intelligence testing; for adults not in school: formal tests addressing intelligence, memory, attention, and other cognitive domains). We will accept any measure of cognitive function that has been previously validated as an appropriate test in this domain.*

* Outcomes intended to be included in the 'Summary of Findings' tables in the completed review. 

Secondary outcomes
  1. Iron status (as reported:ferritin, transferrin saturation, soluble transferrin receptor, soluble transferrin receptor-ferritin index, total iron binding capacity, serum iron).

  2. Physical exercise performance (as defined by trial authors, in particular peak exercise performance (VO2 max/peak- absolute and relative), submaximal exercise performance (heart rate, %VO2 max, energy consumption), and endurance (time)).

  3. Psychological health (for example, depression as defined by the CESD Depression Inventory or visual analogue scales; fatigue as defined by the authors, anxiety as defined by Spielberger State Trait scales).

  4. Adherence (percentage of children who consumed more than 70% of the expected doses).

  5. Anthropometric measures (Z scores for height and weight by age for adolescents, and body mass index for adults).

  6. Serum/plasma zinc (μmol/L).

  7. Vitamin A status (serum/plasma retinol (mmol/L) or retinol binding protein (mmol/L)).

  8. Red cell folate (mmol/L).

For populations in malaria-endemic areas, we will report two additional outcomes:

  • malaria incidence;

  • malaria severity.

If two outcomes evaluate the same construct (for example, iron status evaluated either with ferritin or soluble transferrin receptors), we will treat them separately.

Search methods for identification of studies

Electronic searches

We will search the following databases.

  • Cochrane Central Register of Controlled Trials (CENTRAL)

  • MEDLINE

  • EMBASE

  • CINAHL

  • POPLINE

  • Conference Proceedings Citation Index-Science

  • Science Citation Index

  • WHOLIS

  • IMSEAR

  • PAHO

  • LILACS

  • IBECS

  • EMRO

  • African Index Medicus

We will search for theses using.

  • WorldCat

  • Networked Digital Library of Theses and Dissertations

  • DART-Europe E-theses Portal

  • Australasian Digital Theses Program

  • Theses Canada Portal

  • ProQuest-Dissertations and Theses

In addition, we will search for planned or ongoing trials in International Clinical Trials Registry Platform (ICTRP) and the metaRegister of Controlled Trials (mRCT).

We will use the search strategy in Appendix 1 to search MEDLINE (OVID) and adapt it as required for other electronic databases.

We will not apply any date or language restrictions. If we find articles written in a language other than English, we will commission their translation into English and put them in the awaiting assessment section of the review until translation is completed, at which point we will assess them for eligibility according to the identified inclusion/exclusion criteria. In the event of being unable to secure a translation, we will contact the editorial office of the Cochrane Developmental, Psychosocial and Learning Problems Group for support.

Searching other resources

For assistance in identifying ongoing or unpublished studies, we will contact authors and known experts to identify any additional or unpublished data. We will also contact the Departments of Nutrition for Health and Development and regional offices from the World Health Organization (WHO), and the nutrition section of the Centers for Disease Control and Prevention (CDC), the United Nations Children’s Fund (UNICEF), the World Food Programme (WFP), the Micronutrient Initiative (MI), Helen Keller International (HKI) and Sight and Life Foundation. We will also screen previously published reviews in order to identify other possible studies.

Data collection and analysis

Selection of studies

We will store all studies identified by our search strategy in a reference manager software prior to evaluation. Titles and abstracts of obtained studies will be screened in duplicate. For those studies that are selected as potentially eligible for inclusion, both review authors will be involved in assessing whether they meet the review's inclusion criteria. We will keep records of all eligibility decisions using a digital eligibility form for each study. If study reports contain insufficient information on methods, participants or interventions, we will attempt to contact the authors for further information.

Data extraction and management

We will extract data from studies using a digital extraction form designed for this review. We will first pilot the form on a small number of study reports, and modify it if necessary. For eligible studies, both review authors will independently extract data using the form. SRP will enter data into Review Manager software (RevMan 2011) and LMD will check SRP's data entry for accuracy. We will resolve discrepancies through discussion.

For each study, we will collect data on the following domains.

1. Trial methods:

  • study design;

  • unit and method of allocation;

  • masking of participants and outcomes;

  • exclusion of participants after randomisation and proportion of losses at follow-up.

2. Participants:

  • location of the study;

  • sample size;

  • age;

  • socio-economic status (as defined by trialists and where such information is available);

  • baseline status of anaemia;

  • baseline status of iron deficiency;

  • inclusion and exclusion criteria as described in the Criteria for considering studies for this review.

3. Intervention:

  • additional nutrients;

  • dose of iron;

  • type of iron compound;

  • duration of the intervention;

  • co-intervention.

4. Comparison group:

  • no intervention;

  • placebo;

  • in the case of multiple micronutrient supplements, same nutrients without the nutrient used for the intervention (i.e. iron alone or in combination with folic acid or vitamin C).

5. Outcomes:

We will record both prespecified and non-prespecified outcomes, although we will not use the latter to underpin the conclusions of the review.

When information regarding any of the studies is unclear we will contact the authors of the original reports for further details. If there is insufficient information for us to be able to assess risk of bias, we will put studies into the awaiting assessment section of the review until further information is published, or made available to us.

Assessment of risk of bias in included studies

Both review authors will assess risk of bias using the standard Cochrane 'Risk of bias' tool, in the six specific domains of: sequence generation, allocation concealment, blinding, incomplete outcome data, selective outcome reporting and other issues (Higgins 2011). The following criteria will be applied.

(1) Random sequence generation (checking for selection bias)

We will describe the method used to generate the allocation sequence in sufficient detail to allow an assessment of whether it produces comparable groups as follows:

  • low risk of bias (any truly random process, for example, random number table; computer random number generator);

  • high risk of bias (any non-random process, for example, odd or even date of birth; hospital or clinic record number);

  • unclear risk of bias.

(2) Allocation concealment (checking for possible selection bias)

We will describe the method used to conceal the allocation sequence in sufficient detail to determine whether intervention allocations could have been foreseen in advance of, or during, enrolment as follows:

  • low risk of bias (for example, telephone or central randomisation; consecutively numbered sealed opaque envelopes);

  • high risk of bias (open random allocation; unsealed or non-opaque envelopes);

  • unclear risk of bias.

(3) Blinding of participants and personnel (checking for possible performance bias)

We will describe all measures used, if any, to blind study participants and personnel from knowledge of which intervention a participant received. We will assess the risk of performance bias associated with blinding as:

  • low, high or unclear risk of bias for participants;

  • low, high or unclear risk of bias for personnel.

Whilst assessed separately, we will combine the results into a single evaluation of risk of bias associated with blinding (Higgins 2011).

(4) Blinding of outcome assessment (checking for possible detection bias)

We will describe all measures used, if any, to blind outcome assessors from knowledge as to which intervention a participant received as follows:

  • low risk of bias (blinding);

  • high risk of bias (for example, no blinding of outcome assessment where measurement is likely to be influenced by lack of blinding, or where blinding could have been broken);

  • unclear risk of bias (where insufficient information was provided to permit judgement).

(5) Incomplete outcome data (checking for possible attrition bias through withdrawals, dropouts, protocol deviations)

Outcomes in each included study will be assessed as:

  • low risk of bias: either there were no missing outcome data or the missing outcome data were unlikely to bias the results based on the following considerations: study authors provided transparent documentation of participant flow throughout the study, the proportion of missing data was similar in the intervention and control groups, the reasons for missing data were provided and balanced across intervention and control groups, the reasons for missing data were not likely to bias the results (for example, moving house)

  • high risk of bias: if missing outcome data were likely to bias the results. Studies will also receive this rating if an 'as-treated (per protocol)' analysis is performed with substantial differences between the intervention received and that assigned at randomisation, or if potentially inappropriate methods for imputation have been used

  • unclear risk of bias.

(6) Reporting bias

We will evaluate how the possibility of selective outcome reporting was examined and what was found as follows:

  • low risk of bias (where it is clear that all of the study’s prespecified outcomes and all expected outcomes of interest to the review have been reported);

  • high risk of bias (where not all the study’s prespecified outcomes have been reported; one or more reported primary outcomes were not prespecified; outcomes of interest are reported incompletely and so cannot be used; study fails to include results of a key outcome that would have been expected to have been reported);

  • unclear risk of bias.

(7) Other sources of bias

Was the study free from other problems that could put it at risk of bias?

  • low risk of bias;

  • high risk of bias;

  • unclear risk of bias.

(8) Overall risk of bias

We will summarize the risk of bias at two levels: within studies (across domains) and across studies (for each primary outcome).

For the first, we will assess the likely magnitude and direction of the bias in each of the above mentioned domains and whether we consider they will be likely to impact on the findings. For the first, we will assess the likely magnitude and direction of the bias in each of the above mentioned domains and whether we consider they will likely impact on the findings. We will consider studies at high risk of bias if they have poor or unclear allocation concealment and either inadequate blinding or high/imbalanced losses to follow-up. We will explore the impact of the level of bias through a Sensitivity analysis.

For the assessment across studies, we will set out the main findings of the review in 'Summary of findings' (SoF) tables prepared using GRADE profiler software (GRADEpro 2008). The primary outcomes for each comparison will be listed with estimates of relative effects along with the number of participants and studies contributing data for those outcomes. For each primary outcome, we will assess the quality of the evidence across all trials contributing data using the GRADE approach (Balshem 2010), which involves consideration of within-study risk of bias (methodological quality), directness of evidence, heterogeneity, precision of effect estimates and risk of publication bias. The results will be expressed as one out of  four levels of quality (high, moderate, low or very low). This assessment will be limited only to the trials included in this review.

Measures of treatment effect

Dichotomous data

For dichotomous data, we will present results as risk ratio (RR) with 95% confidence intervals (CI).

Continuous data

For continuous data, we will use the mean difference (MD) with 95% CI if outcomes were measured in the same way between trials. Where some studies have reported endpoint data and other have reported change from baseline data (with errors), we will combine these in the meta-analysis if the outcomes have been reported using the same scale, using MD.

We will use the standardised mean difference (SMD) with 95% CI to combine trials that measure the same outcome but using different measurement methods.

Rates

For rates, if they represent events that could have occurred more than once per participant, we will report them as rate difference, using the methodologies described in Deeks 2011. If rates represent events that could have occurred only once per participant, we will combine them using the approach used for dichotomous data.

Unit of analysis issues

Cluster-randomised trials

We will combine results from both cluster-randomised and individually randomised studies if there is little heterogeneity between the study designs and the interaction between the effect of intervention and the choice of randomisation unit is considered as unlikely.

If the results from cluster trials are not adjusted by authors, we will calculate the trials' effective sample size to account for the effect of clustering in data. We will utilise the intra cluster correlation co-efficient (ICC) derived from the trial (if available), or from another source (for example, using the ICCs derived from other, similar trials and then calculate the design effect with the formula provided in the Cochrane Handbook of Systematic Reviews for Interventions. If this approach is used, we will report this and undertake sensitivity analysis to investigate the effect of variations in ICC).

Studies with multiple intervention groups

For studies with more than two intervention groups (multi-arm studies), we will include the directly relevant arms only. If we identify studies with various relevant arms, we will combine the groups into a single pair-wise comparison (Higgins 2011) and include the disaggregated data in the corresponding subgroup category. If the control group is shared by two or more study arms, we will divide the control group (events and total population) over the number of relevant subgroup categories to avoid double counting the participants. The details will be described in the 'Characteristics of included studies' tables.

Cross-over trials

We will only include the first period of a randomised cross-over trial prior to the wash-out period or to a change in the sequence of treatments. We will treat them as parallel randomised controlled trials.

Dealing with missing data

Missing individuals

We will note the dropout for each included study. Attrition will be noted on the 'Risk of bias' form and included in the 'Risk of bias' summary. We will conduct analysis on an available-case-analysis basis: data will be included from those participants whose results are known. We will consider variation in the degree of missing data as a potential source of heterogeneity.

We will attempt to include all participants randomised to each group in the analyses. If a study reports outcomes only for participants completing the trial or only for participants who followed the protocol, we will contact the authors and ask them to provide additional information to permit analyses according to intention-to-treat principles. If this is not possible, we will perform an available case analysis and we will discuss the extent to which the missing data could alter the results/conclusions of the review. We will assess the sensitivity of any primary meta-analyses to missing data using the strategy recommended by Higgins 2011.

Missing data

Where key data (for example, standard deviations) are missing from the report, we will attempt to contact corresponding authors (or other authors if necessary) of included studies to request unreported data. If this information is not achievable, we will not impute it and will note that the study did not provide data for that particular outcome.

Assessment of heterogeneity

We will assess the methodological heterogeneity by examining the methodological characteristics and risk of bias of the studies, and clinical heterogeneity by examining the similarity between the types of participants, the interventions and the outcomes.

For statistical heterogeneity, we will examine the forest plots from meta-analyses to look for heterogeneity among studies, and use the I2, Tau2, and Chi2 test for heterogeneity statistics to quantify the level of heterogeneity among the trials in each analysis. If we identify substantial heterogeneity (50% or more), we will explore it by prespecified subgroup analysis.

Caution will be advised for interpretation of analyses with high degrees of heterogeneity (75% or more).

Assessment of reporting biases

If more than 10 trials contribute data to the primary outcomes, we will present a funnel plot to evaluate asymmetry and hence a possible indication of publication bias for primary outcomes. Any identified asymmetry could be due to publication bias, but may also be possibly attributable to a real relationship between trial size and effect size (for example, larger trials may have poorer patient supervision and thus compliance to supplementation, which may in turn influence effect size). In such a case, we will include in the discussion a section on the possible causes of the observed asymmetry, including descriptions of reported compliance in the larger as compared with smaller studies. Finally, for the primary outcomes, we will conduct a sensitivity analysis for publication bias by comparing results of published versus unpublished studies.

Data synthesis

We will conduct a meta-analysis to obtain an overall estimate of the effect of treatment when more than one study has examined similar interventions using similar methods, been conducted in similar populations, and measured similar (comparable) outcomes. We will carry out statistical analysis using the Review Manager software (RevMan 2011).

We will use a random-effects meta-analysis for combining data, as we anticipate that there may be natural heterogeneity between studies attributable to the different doses, durations, populations, and implementation/delivery strategies.

Where different studies have reported the same outcomes using both continuous and dichotomous measures, we will re-express odds ratios as standardised mean differences or vice versa and combine the results using the generic inverse-variance method, as described in the Cochrane Handbook for Systematic Reviews of Interventions (Deeks 2011).

Subgroup analysis and investigation of heterogeneity

We will perform the following subgroup analyses only on the primary outcomes:

  1. by age: adolescents (12-18 years), adults (19+ years);

  2. by nutrient: iron alone, iron plus folic acid, iron plus vitamin C;

  3. by baseline anaemia status (as defined by trial authors): anaemic, non anaemic, mixed or unknown;

  4. by baseline iron status (as defined by trial authors): iron deficient, non iron deficient, mixed or unknown;

  5. by baseline iron deficiency anaemia status (as defined by trial authors): iron deficient with anaemia, iron deficient without anaemia, non iron deficient/unknown status of deficiency;

  6. by daily dose of elemental iron supplementation: less than 30 mg, 30 to 60 mg, 61 to 100 mg, 101 mg elemental iron or more;

  7. by duration of iron supplementation: 30 days (one month) or less, more than one month to three months inclusive, more than three months;

  8. by malaria endemicity of the setting in which the study was performed: endemic, not endemic, not reported/unknown.

For meta-analysis including both endpoint and change scores data, we will also conduct a subgroup analysis to separate the effects of the two outcome measures.

We will not conduct subgroup analyses in those outcomes with three or less trials. We will explore the forest plots visually and identify where confidence intervals do not overlap to identify differences between subgroup categories. We will also formally investigate differences between two or more subgroups (Borenstein 2008).

Sensitivity analysis

Sensitivity analysis is planned as follows:

  1. to examine the effects of removing studies at high risk of bias from (studies with poor or unclear allocation concealment and either inadequate blinding or high/imbalanced loss to follow-up) from the analysis;

  2. to examine the effects of different intra cluster correlation values for cluster studies;

  3. to examine the risk of publication bias by excluding unpublished studies;

Acknowledgements

We would like to thank the staff at the editorial office of the Cochrane Developmental, Psychosocial and Learning Problems Group for their support in the preparation of this protocol.

Appendices

Appendix 1. MEDLINE search strategy

  1. Iron/ or Anemia, Iron-Deficiency/ or Iron, Dietary/

  2. Folic Acid/

  3. micronutrients/

  4. Dietary Supplement/

  5. iron$.tw.

  6. (folic$ or folate$ or folvite$ or folacin$ or pteroylglutamic$).tw.

  7. Trace Elements/

  8. (diet$ adj3 supplement$).tw.

  9. (micro-nutrient$ or micronutrient$ or multi-nutrient$ or multinutrient$).tw.

  10. Ferric Compounds/

  11. Ferrous Compounds/

  12. (ferrous$ or ferric$ or fe).tw.

  13. or/1-12

  14. Drug Administration Schedule/

  15. Dose-Response Relationship, Drug/

  16. Time Factors/

  17. (day or daily or week$ or biweek$ or bi-week$ or intermittent$ or alternat$).tw.

  18. or/14-17

  19. 13 and 18

  20. (iron adj3 (dose$ or dosage or administer$ or administration or frequency or regimen$)).tw.

  21. 19 or 20

  22. adult/

  23. middle aged/

  24. adolescent/

  25. (teen$ or adoles$ or pubert$ or pubescen$).tw.

  26. 22 or 23 or 24 or 25

  27. (girl$ or wom#n$ or female$).tw.

  28. female/

  29. 27 or 28

  30. 26 and 29

  31. Menstruation/

  32. (menstruat$ or menstrual$).tw.

  33. or/31-32

  34. 30 or 33

  35. randomized controlled trial.pt.

  36. controlled clinical trial.pt.

  37. randomi#ed.ab.

  38. placebo$.ab.

  39. drug therapy.fs.

  40. randomly.ab.

  41. trial.ab.

  42. groups.ab.

  43. or/35-42

  44. exp animals/ not humans.sh.

  45. 43 not 44

  46. 21 and 34 and 45

Contributions of authors

SRP drafted the background and LMD provided feedback. Both authors contributed to the methods and approved the final manuscript.

Declarations of interest

Sant-Rayn Pasricha - none known.
Luz Maria De-Regil - none known.

Disclaimer: Luz Maria De-Regil is a full-time staff member of the World Health Organization (WHO). The authors alone are responsible for the views expressed in this publication and they do not necessarily represent the official position, decisions, policy or views of this organisation.

Sources of support

Internal sources

  • Evidence and Programme Guidance, Department of Nutrition for Health and Development, World Health Organization, Switzerland.

External sources

  • Dr Sant-Rayn Pasricha is supported by a Victoria Fellowship (Government of Victoria, Australia), a CRB Blackburn Travelling Scholarship (Royal Australasian College of Physicians) and a University of Melbourne Overseas Research Experience Scholarship, Australia.

Ancillary