Calcium and iron deficiency are common in both developed and developing countries. Calcium deficiency can lead to abnormal growth and remodeling of the skeleton, while iron deficiency has profound effects on energy metabolism, work performance, immunity and cognitive function. Supplementation with calcium or iron, or the development of calcium- and iron-fortified foods, can be effective strategies for augmenting low calcium and iron intakes.
However, earlier work had indicated that relatively low levels of dietary calcium (~ 200 mg) could markedly reduce the efficiency of iron absorption from single meals. Surprisingly, it was also shown that calcium could inhibit both heme (meat) iron and non-heme (primarily plant-based) iron, even though they are absorbed in the intestine by different mechanisms. Thus, it has been prudent to try and limit calcium intake in an iron-rich meal to facilitate iron absorption. However, the dose-response relation between calcium intake and inhibition of iron absorption in the fasted state had not been previously explored.
A recently published human absorption study by investigators from Chile and California has now investigated the effects of supplemental calcium (as calcium chloride) on the absorption of iron (as either ferrous sulfate or heme iron). In this study, after an overnight fast, 54 women participated and received various dose of calcium (0, 200, 400, 500, 600, 800, 1000, 1250 or 1500 mg) with either radioactive heme or radioactive non-heme iron at a total iron dose of 5 mg – a typical amount present in a single meal.
The findings of this study were that doses of calcium up to 800 mg had no effect on the absorption of non-heme iron. However, when 1000 mg or more of calcium was ingested along with the iron dose, there was a ~50% reduction in non-heme iron absorption. The investigators did observe that non-heme iron absorption was ~38% lower when the 800 mg calcium dose was consumed, but this difference was not statistically different, and indicates that the 800 mg calcium dose could be detrimental to optimal non-heme iron absorption. This notion was confirmed in a study of calcium effects on heme iron absorption. In that study, the investigators found that 800 mg calcium caused a significant 38% reduction of heme iron absorption.
Thus, it appears that doses around 800 mg or more of calcium will have a negative effect on both heme- and non-heme iron absorption in humans when they are consumed together in the fasted state. Additional studies are needed, however, to determine whether higher doses of iron can overcome the negative effects of calcium.
Source from: Gaitan D et al. Journal of Nutrition. 141:1652-1656;2011.
