Consequences of anaemia
Much of the knowledge pertaining to the health consequences of anaemia comes from cross-sectional, case-control, and prospective studies examining the association between anaemia or haemoglobin on health
outcomes such as maternal mortality, perinatal mortality, and cognitive outcomes, with much of this evidence relating speciﬁ cally to iron-deﬁ ciency anaemia. As such, the causal role and attributable fraction of anaemia toward various outcomes, although highly suggestive, remain to be fully documented.
Maternal and perinatal consequences although the causal evidence for adverse consequences is strong for severe anaemia and maternal outcomes, it remains inconclusive for mild-to-moderate anaemia.
Assimilation of the evidence from six observational studies of anaemia and maternal mortality used to estimate the magnitude of the association found a combined odds ratio (OR) of 0·75 (95% CI 0·62–0·89)
associated with a 10 g/L increase in haemoglobin. relation between anaemia and perinatal mortality also remains inconclusive; on the basis of a meta-analysis of ten studies, the estimated combined OR for perinatal
mortality associated with a 10 g/L increase in haemoglobin was 0·72 (95% CI 0·65–0·81). In a subgroup analysis, the risk in P falciparum malaria endemic areas was greater, with a point estimate of 0·65 (0·56–0·75).
Yet, more recently, evidence from a large prospective cohort study in China of more than 160 000 singleton births did not show an association of maternal anaemia with neonatal mortality.
Several studies have investigated the association between anaemia and adverse birth outcomes, namely preterm birth and low birthweight. These studies have had varied results, with heterogeneity in study designs,
settings, and populations.
These heterogeneous ﬁndings relating maternal anaemia to perinatal outcomes might also be aﬀ ected by the dynamics of haemodilution from ﬁ rst to third trimester, and the timing of haemoglobin measurements.
Several studies have investigated the eﬀ ectiveness of iron supplementation (with or without folic acid) in pregnant women; systematic review of 49 randomised and quasirandomised trials covering 23 200 women showed that treatment with iron or iron and folic acid supplementation during pregnancy was associated with increased haemoglobin concentrations at term, and reduced risk of anaemia or iron deﬁciency at term.
However, there was no signiﬁ cant reduction in infant or maternal outcomes, such as preterm birth and low birthweight.
Despite substantial research into the association between iron deﬁ ciency and cognitive development in children, and several plausible physiological mechanisms, the ability to infer causality from existing studies is limited.
Although observational studies have reported associations between iron-deﬁ ciency anaemia and poor cognitive and motor development, the evidence from randomised trials has again been inconclusive.
In an attempt to quantify this association, a meta-analysis of ﬁ ve studies estimated that a 10 g/L increase in haemoglobin was associated with a 1·73 (95% CI 1·04–2·41) increase in IQ points. However, whether poor cognitive development in irondeﬁ cient children is compounded by other factors aﬀecting social disadvantage, or factors relating to the timing of iron deﬁciency during cognitive development, is unclear.
The association between iron deﬁ ciency and productivity has been extensively investigated. Iron’s role in oxygen transport to muscles and other tissues, and its role in other metabolic pathways, show the direct route by which iron deﬁ ciency can reduce aerobic work capacity.
This link has been supported by randomised ﬁ eld trials of iron supplementation and work productivity in developing countries, including rubber plantation workers in Indonesia, female tea-plantation workers in
Sri Lanka, and female cotton-mill workers in China.
In countries in which physical labour is prevalent, reduced work performance due to anaemia has substantial economic consequences.
Attempts to quantify the economic burden of iron deﬁ ciency have focused on the loss of work productivity in adults and cognitive eﬀ ect in children. The present value of the median physical and cognitive losses
associated with anaemia and iron deﬁ ciency have been estimated at US$3·64 per head, or 0·81% of gross domestic product in selected developing countries.
Although these estimates are based on several assumptions and should be interpreted with caution, they give an idea of the scale of the potential economic consequences of anaemia and iron deﬁ ciency. The
aggregate eﬀ ect of small individual losses, especially in developing economies in which physical labour is dominant, accrues to billions of dollars of human capital—for example, in south Asia, the productivity loss is estimated at $4·2 billion annually.