Effect of iron supplementation on maximal oxygen uptake in female athletes

Effects of Oral Iron Supplementation on Blood Iron Status in Athletes: A Systematic Review, Meta-Analysis and Meta-Regression of Randomized Controlled Trials

BACKGROUND

Iron deficiency in athletes is initially treated with a nutritional intervention. If negative iron balance persists, oral iron supplementation (OIS) can be used. Despite the recent proposal for a refinement of treatment strategies for iron-deficient athletes, there is no general consensus regarding the actual efficiency, dosage, or optimal regimen of OIS.

OBJECTIVE

The aim of this meta-analysis was to evaluate to what extent OIS affects blood iron parameters and physical performance in healthy adult athletes.

METHODS

PubMed, Web of Science, PEDro, CINAHL, SPORTDiscus, and Cochrane were searched from inception to 2 November 2022. Articles were eligible if they satisfied the following criteria: recruited subjects were healthy, adult and physically active individuals, who used exclusively OIS, irrespective of sex and sports discipline.

EXCLUSION CRITERIA

simultaneous supplementation with iron and any other micronutrient(s), intravenous iron supplementation or recent exposure to altitude acclimatisation. The methodological quality of included studies was assessed with the PEDro scale, the completeness of intervention reporting with the TIDieR scale, while the GRADE scale was used for quality of evidence synthesis. The present study was prospectively registered in PROSPERO online registry (ID: CRD42022330230).

RESULTS

From 638 articles identified through the search, 13 studies (n = 449) were included in the quantitative synthesis. When compared to the control group, the results demonstrated that OIS increases serum ferritin (standardized mean difference (SMD) = 1.27, 95% CI 0.44-2.10, p = 0.006), whereas blood haemoglobin (SMD = 1.31, 95% CI - 0.29 to 2.93, p = 0.099), serum transferrin receptor concentration (SMD = - 0.74, 95% CI - 1.89 to 0.41, p = 0.133), and transferrin saturation (SMD = 0.69, 95% CI - 0.84 to 2.22, p = 0.330) remained unaltered. Following OIS, a trend of small positive effect on VO2max (SMD = 0.49, 95% CI - 0.09 to 1.07, p = 0.086) was observed in young healthy athletes. The quality of evidence for all outcomes ranged from moderate to low.

CONCLUSIONS

Increase in serum ferritin concentration after OIS was evident in subjects with initial pre-supplementation serum ferritin concentration ≤ 12 µg/l, while only minimal, if any effect, was observed in subjects with higher pre-supplementation serum ferritin concentration. The doses of OIS, that induced a beneficial effect on hematological parameters differed from 16 to 100 mg of elementary iron daily, over the period between 6 and 8 weeks. Shorter supplementation protocols have been shown to be ineffective.

Association of red blood cell size and physical fitness in a military male cohort: The CHIEF study

Anemia manifested as reduced red blood cell (RBC) amounts or hemoglobin levels has been associated with lower cardiorespiratory fitness. However, the relationship of smaller RBC with physical fitness was unknown. We included 2933 non-anemic military males (hemoglobin levels: 11.1-15.9 g/dL and mean corpuscular volume (MCV) <100 fL) in Taiwan during 2014. Aerobic fitness was assessed by time for a 3000-meter run, and anaerobic fitness was evaluated by numbers of sit-ups and push-ups, each performed within 2 minutes. Multiple linear and logistic regression models adjusting for age, service specialty, lipid profiles, and hemoglobin levels were used to determine the associations. Microcytosis and normocytosis were defined as MCV ≤ 70 fL (n = 190) and MCV > 70 fL (n = 2743), respectively. The linear regression shows that as compared with microcytosis, normocytosis was associated with more numbers of sit-ups performed within 2 minutes (β = 1.51, P-value = 0.02). The logistic regression also reveals that those males with microcytosis had higher probability as the worst 10% performers in the 2-minute push-up test (odds ratio: 1.91, 95% confidence intervals: 1.18-3.12). By contrast, there was no association of microcytosis with 3000-meter running time. Our study suggests that non-anemic microcytosis was associated with lower anaerobic fitness but not with aerobic fitness. Whether the causative factors for microcytosis such as iron deficiency status and thalassemia trait unavailable in the study might account for the relationship needs further investigations.

Effects of dietary arginine on intestinal antioxidant status and immunity involved in Nrf2 and NF-κB signaling pathway in juvenile blunt snout bream, Megalobrama amblycephala

The present study assessed the effects of dietary arginine on intestinal antioxidant status and immunity involved in Nrf2 and NF-κB signaling pathway in juvenile blunt snout bream. Fish were fed three practical diets with graded arginine levels (0.87%, 1.62% and 2.70%) for 8 weeks. Compared with the control group (0.87%), the counts of white blood cell (WBC), red blood cell (RBC) and hemoglobin (HGB) content were significantly improved at dietary arginine levels of 1.62% (P<0.05). Plasma albumin (ALB) levels and alkaline phosphatase (ALP) activities were significantly improved at dietary arginine levels of 1.62% and 2.70% (P < 0.05). Alanine transaminase (ALT) activity was decreased in fish fed with 1.62% dietary arginine level (P<0.05). Plasma glutathione peroxidase (GPx) activities, copper-zinc superoxide dismutase (Cu/Zn-SOD) activities, total antioxidant capacity (T-AOC) activities and glutathione (GSH) levels were significantly increased at dietary arginine levels of 1.62% and 2.70% (P<0.05). Plasma total superoxide dismutase (T-SOD) activities and catalase (CAT) activities were significantly improved in fish fed with 1.62% dietary arginine level. Significantly higher manganese superoxide dismutase (Mn-SOD) activity was observed in fish fed with 1.62% dietary arginine level compared with 2.70% dietary arginine level (P<0.05). 1.62% and 2.70% dietary arginine levels significantly lowered malondialdehyde (MDA) levels. The relative expression of nuclear factor erythroid 2-related factor 2 (Nrf2) was significantly increased in fish fed with 1.62% dietary arginine level, inversely, the relative expression of Kelch-like ECH-associated protein 1 (Keap1) showed a converse trend. 1.62% and 2.70% dietary arginine levels significantly improved the relative expressions of Cu/Zn-SOD, GPx and CAT. Furthermore, 2.70% dietary arginine level significantly lowered the relative expression of Mn-SOD compared with the control group and 1.62% dietary arginine levels. The relative expressions of Interleukin 1β (IL-1β), tumour necrosis factor-α (TNF-α) and nuclear factor-kappa B (NF-κB) were lowered in fish fed with 1.62% dietary arginine level. 1.62% and 2.70% dietary arginine levels significantly improved the relative expressions of transforming growth factor-β (TGF-β). Hematocrit (HCT), aspartate aminotransferase (AST) activities, interleukin 8 (IL-8) and interleukin 10 (IL-10) expressions were not significantly affected by the graded dietary arginine levels. These results suggest that the optimal dietary arginine level plays an important role in enhancing antioxidant and immune status to maintain the intestinal health of juvenile blunt snout bream.

Iron balance and iron supplementation for the female athlete: A practical approach

Maintaining a positive iron balance is essential for female athletes to avoid the effects of iron deficiency and anaemia and to maintain or improve performance. A major function of iron is in the production of the oxygen and carbon dioxide carrying molecule, haemoglobin, via erythropoiesis. Iron balance is under the control of a number of factors including the peptide hormone hepcidin, dietary iron intake and absorption, environmental stressors (e.g. altitude), exercise, menstrual blood loss and genetics. Menstruating females, particularly those with heavy menstrual bleeding are at an elevated risk of iron deficiency. Haemoglobin concentration [Hb] and serum ferritin (sFer) are traditionally used to identify iron deficiency, however, in isolation these may have limited value in athletes due to: (1) the effects of fluctuations in plasma volume in response to training or the environment on [Hb], (2) the influence of inflammation on sFer and (3) the absence of sport, gender and individually specific normative data. A more detailed and longitudinal examination of haematology, menstrual cycle pattern, biochemistry, exercise physiology, environmental factors and training load can offer a superior characterisation of iron status and help to direct appropriate interventions that will avoid iron deficiency or iron overload. Supplementation is often required in iron deficiency; however, nutritional strategies to increase iron intake, rest and descent from altitude can also be effective and will help to prevent future iron deficient episodes. In severe cases or where there is a time-critical need, such as major championships, iron injections may be appropriate.

Daily iron supplementation for improving anaemia, iron status and health in menstruating women

BACKGROUND

Iron-deficiency anaemia is highly prevalent among non-pregnant women of reproductive age (menstruating women) worldwide, although the prevalence is highest in lower-income settings. Iron-deficiency anaemia has been associated with a range of adverse health outcomes, which restitution of iron stores using iron supplementation has been considered likely to resolve. Although there have been many trials reporting effects of iron in non-pregnant women, these trials have never been synthesised in a systematic review.

OBJECTIVES

To establish the evidence for effects of daily supplementation with iron on anaemia and iron status, as well as on physical, psychological and neurocognitive health, in menstruating women.

SEARCH METHODS

In November 2015 we searched CENTRAL, Ovid MEDLINE, EMBASE, and nine other databases, as well as four digital thesis repositories. In addition, we searched the World Health Organization International Clinical Trials Registry Platform (WHO ICTRP) and reference lists of relevant reviews.

SELECTION CRITERIA

We included randomised controlled trials (RCTs) and quasi-RCTs comparing daily oral iron supplementation with or without a cointervention (folic acid or vitamin C), for at least five days per week at any dose, to control or placebo using either individual- or cluster-randomisation. Inclusion criteria were menstruating women (or women aged 12 to 50 years) reporting on predefined primary (anaemia, haemoglobin concentration, iron deficiency, iron-deficiency anaemia, all-cause mortality, adverse effects, and cognitive function) or secondary (iron status measured by iron indices, physical exercise performance, psychological health, adherence, anthropometric measures, serum/plasma zinc levels, vitamin A status, and red cell folate) outcomes.

DATA COLLECTION AND ANALYSIS

We used the standard methodological procedures of Cochrane.

MAIN RESULTS

The search strategy identified 31,767 records; after screening, 90 full-text reports were assessed for eligibility. We included 67 trials (from 76 reports), recruiting 8506 women; the number of women included in analyses varied greatly between outcomes, with endpoint haemoglobin concentration being the outcome with the largest number of participants analysed (6861 women). Only 10 studies were considered at low overall risk of bias, with most studies presenting insufficient details about trial quality.Women receiving iron were significantly less likely to be anaemic at the end of intervention compared to women receiving control (risk ratio (RR) 0.39 (95% confidence interval (CI) 0.25 to 0.60, 10 studies, 3273 women, moderate quality evidence). Women receiving iron had a higher haemoglobin concentration at the end of intervention compared to women receiving control (mean difference (MD) 5.30, 95% CI 4.14 to 6.45, 51 studies, 6861 women, high quality evidence). Women receiving iron had a reduced risk of iron deficiency compared to women receiving control (RR 0.62, 95% CI 0.50 to 0.76, 7 studies, 1088 women, moderate quality evidence). Only one study (55 women) specifically reported iron-deficiency anaemia and no studies reported mortality. Seven trials recruiting 901 women reported on 'any side effect' and did not identify an overall increased prevalence of side effects from iron supplements (RR 2.14, 95% CI 0.94 to 4.86, low quality evidence). Five studies recruiting 521 women identified an increased prevalence of gastrointestinal side effects in women taking iron (RR 1.99, 95% CI 1.26 to 3.12, low quality evidence). Six studies recruiting 604 women identified an increased prevalence of loose stools/diarrhoea (RR 2.13, 95% CI 1.10, 4.11, high quality evidence); eight studies recruiting 1036 women identified an increased prevalence of hard stools/constipation (RR 2.07, 95% CI 1.35 to 3.17, high quality evidence). Seven studies recruiting 1190 women identified evidence of an increased prevalence of abdominal pain among women randomised to iron (RR 1.55, 95% CI 0.99 to 2.41, low quality evidence). Eight studies recruiting 1214 women did not find any evidence of an increased prevalence of nausea among women randomised to iron (RR 1.19, 95% CI 0.78 to 1.82). Evidence that iron supplementation improves cognitive performance in women is uncertain, as studies could not be meta-analysed and individual studies reported conflicting results. Iron supplementation improved maximal and submaximal exercise performance, and appears to reduce symptomatic fatigue. Although adherence could not be formally meta-analysed due to differences in reporting, there was no evident difference in adherence between women randomised to iron and control.

AUTHORS' CONCLUSIONS

Daily iron supplementation effectively reduces the prevalence of anaemia and iron deficiency, raises haemoglobin and iron stores, improves exercise performance and reduces symptomatic fatigue. These benefits come at the expense of increased gastrointestinal symptomatic side effects.

Iron supplementation prevents a decline in iron stores and enhances strength performance in elite female volleyball players during the competitive season

The primary aim of this study was to examine the effects of 11 weeks of iron supplementation on hematological and strength markers in elite female volleyball players. Twenty-two volleyball players (aged 27.0 ± 5.6 years) from 2 Spanish First National League teams participated and were counterbalanced into 1 of 2 groups based upon iron status: (i) control group (CG, n = 11); or (ii) iron treatment group (ITG, n = 11), which received 325 mg/day of ferrous sulphate daily. Subjects performed their team's regimen of training or match play every day. Both groups were tested for hematological and strength levels at 2 points: (i) baseline (T0, before preseason) and (ii) 11 weeks later (T11, post-testing). Hematological parameters were serum iron (sFe), serum ferritin (FER), transferrin saturation index (TSI), and hemoglobin (Hb); strength assessments were bench press, military press, half-squat, power clean, clean and jerk, and pull-over. CG experienced a significant decrease (p < 0.05) for sFe (T0, 112.7 ± 31.5; T11, 69.0 ± 20.5 μg·dL(-1); -33.9%), FER (T0, 60.2 ± 28.6; T11, 38.2 ± 16.4 ng·mL(-1); -34.6%), TSI (T0, 29.4% ± 9.5%; T11, 17.4% ± 5.1%; -35.3%), and Hb (T0, 14.1 ± 1.0; T11, 13.0 ± 0.8 g·L(-1); -7.44%); however, ITG experienced no changes (p > 0.05). Consequently, in ITG all hematological parameters were significantly greater (p < 0.05) than CG at T11. There was greater (p < 0.05) percent increase in the clean and jerk (CG: +5.1% ± 20.9 vs. ITG: +29.0% ± 21.3%), power clean (CG: -5.8% ± 30.3% vs. ITG: +44.6% ± 56.6%), and total mean strength (CG: +10.9% ± 3.2% vs. ITG: +26.2% ± 3.6%) in ITG. Our findings suggest that oral iron supplementation prevents iron loss and enhances strength in female volleyball players during the competitive season.

Iron supplementation benefits physical performance in women of reproductive age: a systematic review and meta-analysis

Animal and human observational studies suggest that iron deficiency impairs physical exercise performance, but findings from randomized trials on the effects of iron are equivocal. Iron deficiency and anemia are especially common in women of reproductive age (WRA). Clear evidence of benefit from iron supplementation would inform clinical and public health guidelines. Therefore, we performed a systematic review and meta-analysis to determine the effect of iron supplementation compared with control on exercise performance in WRA. We searched the Cochrane Central Register of Clinical Trials, MEDLINE, Scopus (comprising Embase and MEDLINE), WHO regional databases, and other sources in July 2013. Randomized controlled trials that measured exercise outcomes in WRA randomized to daily oral iron supplementation vs. control were eligible. Random-effects meta-analysis was used to calculate mean differences (MDs) and standardized MDs (SMDs). Risk of bias was assessed using the Cochrane risk-of-bias tool. Of 6757 titles screened, 24 eligible studies were identified, 22 of which contained extractable data. Only 3 studies were at overall low risk of bias. Iron supplementation improved both maximal exercise performance, demonstrated by an increase in maximal oxygen consumption (VO2 max) [for relative VO2 max, MD: 2.35 mL/(kg ⋅ min); 95% CI: 0.82, 3.88; P = 0.003, 18 studies; for absolute VO2 max, MD: 0.11 L/min; 95% CI: 0.03, 0.20; P = 0.01, 9 studies; for overall VO2 max, SMD: 0.37; 95% CI: 0.11, 0.62; P = 0.005, 20 studies], and submaximal exercise performance, demonstrated by a lower heart rate (MD: -4.05 beats per minute; 95% CI: -7.25, -0.85; P = 0.01, 6 studies) and proportion of VO2 max (MD: -2.68%; 95% CI: -4.94, -0.41; P = 0.02, 6 studies) required to achieve defined workloads. Daily iron supplementation significantly improves maximal and submaximal exercise performance in WRA, providing a rationale to prevent and treat iron deficiency in this group. This trial was registered with PROSPERO (http://www.crd.york.ac.uk/PROSPERO/prospero.asp) as CRD42013005166.

Control of iron deficiency anemia in low- and middle-income countries

Despite worldwide economic and scientific development, more than a quarter of the world’s population remains anemic, and about half of this burden is a result of iron deficiency anemia (IDA). IDA is most prevalent among preschool children and women. Among women, iron supplementation improves physical and cognitive performance, work productivity, and well-being, and iron during pregnancy improves maternal, neonatal, infant, and even long-term child outcomes. Among children, iron may improve cognitive, psychomotor, and physical development, but the evidence for this is more limited. Strategies to control IDA include daily and intermittent iron supplementation, home fortification with micronutrient powders, fortification of staple foods and condiments, and activities to improve food security and dietary diversity. The safety of routine iron supplementation in settings where infectious diseases, particularly malaria, are endemic remains uncertain. The World Health Organization is revising global guidelines for controlling IDA. Implementation of anemia control programs in developing countries requires careful baseline epidemiologic evaluation, selection of appropriate interventions that suit the population, and ongoing monitoring to ensure safety and effectiveness. This review provides an overview and an approach for the implementation of public health interventions for controlling IDA in low- and middle-income countries, with an emphasis on current evidence-based recommendations.