If you have read some of my previous articles you will be aware that for large portions of the population, the intake of many minerals, such as calcium and zinc, is inadequate for optimum health. This is due to depletion of minerals from the soils because of over farming. Subsequently, the foods that that are grown in these soils are deficient in minerals and when we eat these foods we too become mineral deficient. Zinc in an important trace mineral and deficiencies are widely reported in the scientific literature. Supplementation of zinc is popular and many people, particularly athletes, choose to augment their diet with zinc tablets. However, mineral absorption is complex and evidence suggests that calcium and zinc may compete for absorption. This interaction between calcium and zinc may therefore be problematic in terms of nutrient absorption and optimal mineral status.
For example, a study in the American Journal of Nutrition in 1997 reported that feeding healthy subjects 468 mg of dicalcium phosphate a day, or an equivalent amount of calcium from milk, reduced net zinc absorption by around 2mg. In the low calcium diet, only 2 of 18 subject had a negative zinc balance, but this number increased to 10 with addition of the calcium supplement. Increased faecal excretion confirmed that reduced absorption in the gut was the cause of the negative zinc balance. In a second experiment, the researchers fed subjects a single beef based meal containing 7.3 mg of zinc. Absorption from the meal was 1.47 mg, but this fell to 0.75 mg with addition of 600 mg of calcium (as carbonate). This reduction was reversed with a 7.8 mg zinc supplement.
Normal zinc absorption from the gut is around 20 % of the ingested zinc. From this study it would appear that calcium inhibits zinc absorption substantially, and the authors recommended supplementation with 10 mg of extra zinc to counteract the high calcium intake. Supplements that contain zinc often also contain dicalcium phosphate as a binder in the tablets, and most multivitamins will contain both calcium in the ingredients and dicalcium phosphate as a binder. It is therefore recommended that this is taken this into account when calculating zinc requirements, and that taking additional zinc to counteract the reduced absorption is considered. It would also seem sensible to take zinc supplements away from calcium containing meals, especially milk or food that contains milk.
RdB
