Can calcium and iron supplements be taken together? On the Internet, rumor has it that taking calcium and iron together will interfere with iron absorption, and the two will have a competitive effect. Therefore, they should not be taken at the same time. It would be better to have at least 2 hours apart when supplementing the two. Many professionals or institutions also claim that iron cannot be consumed with calcium. Is it true? Is it completely ineffective to take calcium while supplementing iron? Let's take a look at the scientific part of the evidence.

Many short-term studies have pointed out that calcium will affect the absorption of iron, but those studies mainly focus on the results of simultaneous consumption of a single taken. In fact, according to the research under the state of long-term consumption, in which the investigation aimed on different dietary composition and other factors, the result showed that calcium supplements does not have a significant effect on the absorption rate of iron supplements.

The accuracy of these studies indicated that calcium and iron will interfere with each other's absorption has actually been questioned by many. The magnitude of the influence of the absorption rate seems to vary according to different research designs, including the time point of measuring the absorption rate and the method of measuring the absorption rate.

In addition, there were some studies investigated whether dairy foods affect iron absorption. In a randomized crossover study of a four-day diet, in which it focused on drinking a glass of milk at the same time in each meal of three meals, or eating calcium-fortified foods with the same calcium content. The result discovered that the doing did not affect the absorption of non-heme iron. In another diet study based on plant and vegetables, the additional consumption of milk or yogurt at the same time didn’t affect the bioavailability of iron.

In a 2010 study, it was found that the absorption rate of calcium and iron may have a slight impact on the short-term. However, as a matter of fact, the human colonic mucosal cells have a so-called rebound effect in their gene expression; mucosal cells will adapt and further increase the absorption rate of iron. Thus, the long-term consumption will not cause insufficient iron absorption or even deficiency. To conclude, can we take calcium and iron supplements at the same time? The answer is “yes” according to the results of many studies. No need to worry at all.

《 References 》

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9. Rosado JL et al. The addition of milk or yogurt to a plant-based diet increases zinc bioavailability but does not affect iron bioavailability in women. J Nutr 2005;135(3):465-8.