Humans absorb most minerals in the small intestine, and both active and passive proc-esses transport them into the blood for distribution and use throughout the body. Mineral absorption is influenced by their bioavailability, the ability of nutrients to be absorbed and utilized in the body, which is itself affected by various factors. One such factor is nutritional status. When a person is deficient in a mineral or the needs for that mineral have increased, the absorption and bioavailability of that mineral tends to increase. For instance, during pregnancy, a woman’s body absorbs calcium more efficiently than usual. Likewise, people absorb less of minerals if they already get enough. It’s important to note, however, that although absorption of minerals slows during overconsumption, it doesn’t stop—so it is still possible to consume excess, or even toxic, amounts of minerals. When mineral levels in the body increase, the excess is typically excreted in the urine.

The presence of dietary elements called binders can also influence mineral absorption. Binders such as phytates, found in whole cereal grains; oxalates, found in spinach and some vegetables; and polyphenols, present in coffee and tea, can limit bioavailability by chemically binding to minerals. Minerals can also compete with one another for absorption. For example, excess iron consumption from supplements can interfere with zinc absorption. Finally, the presence of certain vitamins can also affect bioavailability. Vitamin D, for instance, actually boosts absorption of calcium and phosphorus.