Iron considerations for the athlete: a narrative review

The estimated prevalence of iron deficiency in the world suggests that there should be widespread negative consequences of this nutrient deficiency in both developed and developing countries. In considering the reality of these estimates, the Belmont Conference seeks to reconsider the accepted relationships of iron status to physiological, biochemical and neurological outcomes. This review focuses on the biological processes that we believe are the basis for alterations in the immune system, neural systems, and energy metabolism and exercise. The strength of evidence is considered in each of the domains and the large gaps in knowledge of basic biology or iron-dependent processes are identified. Iron is both an essential nutrient and a potential toxicant to cells; it requires a highly sophisticated and complex set of regulatory approaches to meet the demands of cells as well as prevent excess accumulation. It is hoped that this review of the more basic aspects of the biology of iron will set the stage for subsequent in-depth reviews of the relationship of iron to morbidity, mortality and functioning of iron-deficient individuals and populations.

Background The tolerability of oral iron supplementation for the treatment of iron deficiency anemia is disputed. Objective Our aim was to quantify the odds of GI side-effects in adults related to current gold standard oral iron therapy, namely ferrous sulfate. Methods Systematic review and meta-analysis of randomized controlled trials (RCTs) evaluating GI side-effects that included ferrous sulfate and a comparator that was either placebo or intravenous (IV) iron. Random effects meta-analysis modelling was undertaken and study heterogeneity was summarised using I2 statistics. Results Forty three trials comprising 6831 adult participants were included. Twenty trials (n = 3168) had a placebo arm and twenty three trials (n = 3663) had an active comparator arm of IV iron. Ferrous sulfate supplementation significantly increased risk of GI side-effects versus placebo with an odds ratio (OR) of 2.32 [95% CI 1.74–3.08, p<0.0001, I2 = 53.6%] and versus IV iron with an OR of 3.05 [95% CI 2.07-4.48, p<0.0001, I2 = 41.6%]. Subgroup analysis in IBD patients showed a similar effect versus IV iron (OR = 3.14, 95% CI 1.34-7.36, p = 0.008, I2 = 0%). Likewise, subgroup analysis of pooled data from 7 RCTs in pregnant women (n = 1028) showed a statistically significant increased risk of GI side-effects for ferrous sulfate although there was marked heterogeneity in the data (OR = 3.33, 95% CI 1.19-9.28, p = 0.02, I2 = 66.1%). Meta-regression did not provide significant evidence of an association between the study OR and the iron dose. Conclusions Our meta-analysis confirms that ferrous sulfate is associated with a significant increase in gastrointestinal-specific side-effects but does not find a relationship with dose.

This review updates and complements the review of energy balance and body composition in the Proceedings of the 2003 IOC Consensus Conference on Sports Nutrition. It argues that the concept of energy availability is more useful than the concept of energy balance for managing the diets of athletes. It then summarizes recent reports of the existence, aetiologies, and clinical consequences of low energy availability in athletes. This is followed by a review of recent research on the failure of appetite to increase ad libitum energy intake in compensation for exercise energy expenditure. The review closes by summarizing the implications of this research for managing the diets of athletes.