Zinc: Interactions

Interactions of zinc with other micronutrients (vital substances):

Folic acid

The relationship between folic acid and zinc is controversial: Folate bioavailability may be increased by a zinc-dependent enzyme. In some studies, it was clear that low zinc intake decreased folate absorption; other studies show that supplemental folic acid impaired zinc utilization in individuals with low zinc status.

A more recent study, on the other hand, showed that neither the additional administration of 800 µg folic acid/day for 25 days affected zinc status nor did supplemental zinc intake affect folate utilization.

Calcium

Consumption of 468 mg calcium in the form of milk or as calcium phosphate-in addition to a diet containing 890 mg calcium and 17.6 mg zinc-reduced zinc absorption and affected zinc balance in postmenopausal women. Again, there are also studies that showed no effect on zinc absorption in postmenopausal women. In young women, young as well as older men, and also breastfeeding women, it has also been shown that increased calcium intake (between 230 mg to 2,000 mg daily) decreases zinc absorption. However, this had no effect on zinc excretion and zinc balance. Therefore, the interaction between calcium and zinc may be compensated in the long term.

Iron

In contrast to normal dietary iron intake, the additional administration of iron by dietary supplementation at the dose of 38-65 mg elemental iron/day may decrease zinc absorption. This interaction is of particular concern during pregnancy and lactation, so some experts advise women who take more than 60 mg of supplemental elemental iron during this time to also use a zinc supplement. On the subject of intake, see the “Intake” category of this encyclopedia.

Copper

Consuming large amounts of zinc (more than 50 mg/day) for several weeks can decrease the bioavailability of copper. Increased zinc consumption results in increased intestinal synthesis of a copper-binding protein called metallothionein. Metallothionein traps copper within intestinal cells, preventing its absorption. In contrast, normal zinc intake does not affect copper absorption; increased copper consumption also does not affect zinc absorption.

Further

Foods with a high content of phytic acid (phytates) – e.g. cereal products, legumes, nuts – reduce the absorption of minerals and trace elements such as calcium, magnesium, iron and zinc. The cause is the formation of insoluble phytate complexes. For tannins, for example present in green and black tea, comparable effects have been demonstrated in some scientific studies. In contrast, this does not seem to apply to oxalates – rhubarb, for example, has a high content of oxalic acid. In a balanced diet (mixed diet), the intake of phytates and tannins has no significant effect on zinc absorption and zinc supply.