Experts have warned against some common mistakes when taking iron supplements, stressing that the timing of taking them and the accompanying foods and drinks may affect their absorption and effectiveness.
Iron supplements are used to treat iron-deficiency anemia, but they can cause side effects in some people, such as nausea, constipation, diarrhea, and stomach pain. Taking the supplement with food may help alleviate these symptoms, although iron absorption is generally better on an empty stomach.
Rachel Woods, an associate professor of medical education at the Universities of Nottingham and Lincoln, wrote on The Conversation that iron deficiency should not be treated by simply taking supplements indiscriminately, as its causes can include blood loss or malabsorption of iron, including conditions affecting the intestines. Therefore, it is important to diagnose iron deficiency and identify its cause before starting treatment.
Woods explained that certain drinks, foods, and other supplements can affect the amount of iron the body absorbs, pointing specifically to coffee.
A small study of 34 women with iron deficiency showed that drinking coffee with a 100 mg iron supplement reduced iron absorption by 54% compared to taking it with water. Absorption was also reduced by 66% when the supplement was taken with breakfast, even though the breakfast included orange juice.
In contrast, the study showed that taking 80 mg of vitamin C increased iron absorption by 30%, while raising the dose to 500 mg did not achieve any additional improvement.
The results also indicated that iron absorption was 37% lower in the afternoon compared to the morning, but Woods explained that this result was close to the usual lower bound for statistical significance, and therefore cannot be considered a general rule recommending iron intake in the morning.
Improving iron absorption does not necessarily mean better treatment outcomes, according to Woods. A randomized trial involving 440 adults with iron-deficiency anemia showed that iron alone was just as effective as iron with vitamin C in improving hemoglobin levels and iron stores.
Calcium may also affect iron absorption, especially when taken together in large amounts. However, a systematic review of human studies found that the long-term effect of calcium on iron levels in the body was limited.
Therefore, Woods advises those taking calcium and iron supplements together to consult a pharmacist about the possibility of separating the times when taking the two supplements.
Iron is generally absorbed better when taken on an empty stomach, but this may increase side effects in some people. The UK's National Health Service (NHS) recommends taking ferrous sulfate about 30 minutes before or two hours after meals, if possible. If it causes stomach upset, it can be taken with or after food.
Woods believes that adhering to the method of taking the supplement and avoiding missing doses is more important than striving for the best possible absorption, especially if this leads to irregularity in treatment.
Woods warned against taking dietary supplements without a clear need or without consulting a specialist, stressing that high doses of some supplements may cause health problems.
She explained that excessive intake of vitamin B12 has been linked to nerve damage, while some fat-soluble vitamins, most notably vitamin A, can accumulate in the body and reach toxic levels when consumed in large quantities.
Therefore, the safe use of iron supplements depends not only on taking them, but also on knowing the cause of the iron deficiency, adhering to the recommended dosage, and paying attention to foods, drinks, and supplements that may affect their absorption.
