Because of their similarities, strontium and calcium compete in the body. For example, strontium competes with calcium for absorption, notably in the intestines and renal tubules.[1] Calcium tends to be preferred physiologically, though, so taking the two minerals together may reduce the absorption and retention of strontium. Strontium absorption is reduced by phosphate and increased by vitamin D.[2] For these reasons, supplement labels will often recommend taking these supplements separately and also ensuring that adequate calcium is consumed.[3][4][1]
As we age, how the body differentiates between strontium and calcium can vary. In early childhood, during bone development, excess exposure to strontium can impede bone growth and cause strontium-induced rickets. Though these risks are not as concerning for adults, strontium can still interfere with normal bone development when taken in circumstances where vitamin D, phosphorus, and calcium intakes are insufficient.[2][5]
In observational evidence on hypertension in pregnancy, higher blood strontium levels were associated with hypertensive disorders, but a clear cause-and-effect relationship could not be determined.[6]