Iron supplements are used to treat anemia resulting from iron deficiency, but taking them may cause some people side effects such as nausea, constipation, diarrhea, and stomach pain. Taking the supplement with food may help relieve these symptoms, although iron absorption is usually better on an empty stomach.
Rachel Woods, associate professor of medical education at the Universities of Nottingham and Lincoln, wrote on the Conversation website that iron deficiency should not be treated by taking supplements indiscriminately, because its causes may include blood loss or malabsorption of iron, including conditions that affect the intestines. Therefore, it is important to diagnose iron deficiency and determine its cause before starting treatment.
Coffee may reduce iron absorption
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 that included 34 women with iron deficiency showed that consuming coffee with a supplement containing 100 mg of iron resulted in a 54% decrease in iron absorption compared to taking it with water. Absorption also decreased by 66% when taking the supplement with breakfast, even though the meal contained orange juice.
On the other hand, 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 limit for statistical significance, and therefore cannot be considered a general rule recommending iron intake in the morning.
Does iron need vitamin C?
Improving iron absorption does not necessarily mean better treatment outcomes, according to Woods. A randomized trial that included 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.
What about calcium?
Calcium may also affect iron absorption, especially when taken together and in large quantities. However, a systematic review of human studies found that the effect of calcium on iron levels in the body in the long term was limited.
Therefore, Woods advises those who take calcium and iron supplements together to consult a pharmacist about the possibility of separating the dates of taking the two supplements.
The best time to take iron
The body usually absorbs iron better when taken on an empty stomach, but this may increase side effects in some people. The British National Health Service (NHS) advises taking ferrous sulfate about 30 minutes before food or two hours after it, 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 to achieve the best possible absorption, especially if this leads to irregularity in treatment.
Excessive supplementation may be harmful
Woods warned against taking nutritional supplements without a clear need or without consulting a specialist, stressing that high doses of some supplements may cause health harm.
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 does not depend on taking them only, but on knowing the cause of iron deficiency, adhering to the recommended dose, and paying attention to foods, drinks, and supplements that may affect their absorption.
