Most nutrients work well in pairs, but some refuse to play nice, according to Harvard University researchers. Zinc and copper compete to be absorbed in your small intestine. Too much zinc forfeits copper—which leads to copper deficiency. (Daily recommended zinc intake is 11 milligrams for men and 8 mg for women. And adults need 900 micrograms of copper daily.)

In children, too much calcium and not enough iron is cause for concern. When these two minerals overlap, it interferes with the body’s ability to absorb them, says Jenna Bell-Wilson, PhD, RD, coauthor of Energy to Burn.

In addition, it’s important to know that children’s calcium and iron intake varies by age. (Translation: Parents should discuss their child’s diet with a pediatrician.)

Worried whether you get enough nutrients? Don’t be.

“This is a greater concern if you are focusing on supplements and taking more than you require,” Wilson says. “If your diet is varied and you eat an assortment of foods daily, this shouldn’t be an issue.”