Two studies, both published in July of this year, have linked high consumption of heme iron (the form of iron found in animal products) with an increased risk of developing gestational diabetes.
The first study was conducted by researchers from the Center for Perinatal Studies at the Swedish Medical Center in Washington, USA, and involved the study of 3,158 pregnant women who were followed over the course of their pregnancy. During the study, 158 of the women developed gestational diabetes. The researchers found that women who reported the highest intake of heme iron, more than 1.5mg per day, were 3.3 times more likely to develop gestational diabetes than women who consumed less than 0.48mg per day. The researchers calculated that each 1mg per day increase in heme iron intake increased the risk of gestational diabetes by 51%. For comparison, a serving of porterhouse steak contains around 2mg of heme iron.
Interestingly, intake of non-heme iron, which is found in plants, was negatively correlated with gestational diabetes risk although this was not statistically significant.
The second study was published in the journal Diabetes Care and involved 13,475 from the Nurses Health Study II. Researchers in that study found that women in the highest quintile for heme iron intake (more than 1.6mg per day) were 58% more likely to develop gestational diabetes than women in the lowest quintile (less than 0.66mg per day). Neither dietary non-heme iron nor supplemental iron intake were associated with gestational diabetes risk in the study.
Iron is a potent catalyst for the production of reactive oxygen species which cause damage to cells in the body. Beta cells located in the pancreas, which are responsible for the production and release of insulin, are particularly susceptible to oxidative damage. Furthermore, iron appears to accumulate readily in the pancreas due to high expression of DMT-1, which is a protein involved in the transportation of several metal ions in the body including iron. This suggests a mechanism linking excessive iron intake to diabetes where-by high levels of iron accumulate in the pancreas leading to iron induced oxidative damage of pancreatic beta-cells and a subsequent drop in the ability of the pancreas to secrete insulin.
Heme iron is absorbed more readily than non-heme iron which might explain why only heme iron intake appears to increase the risk of developing gestational diabetes.
Gestational diabetes typically occurs during the third trimester of pregnancy. Although the condition usually resolves itself following birth, women who have suffered gestational diabetes have a greater risk of developing type-2 diabetes in later life. One study found that mothers who had gestational diabetes were 7.43 times more likely to subsequently develop type-2 diabetes than mothers who had normal blood sugar levels during pregnancy. Both pre-term delivery and complications during birth are also marginally more common in mothers with gestational diabetes. The prevalence of gestational diabetes is estimated to be around 5% in the United States however the true figure may be higher as asymptomatic women often go undiagnosed. Symptoms of gestational diabetes are similar to those of regular diabetes and include excessive thirst and urination, fatigue, and nausea.
The results above suggest that women should exercise caution before beginning iron supplementation during pregnancy. While anaemia is a risk during, and immediately after pregnancy due to increased blood loss, it is not typically a life threatening condition and the risks of iron supplementation may well outweigh any benefits.
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