Recommendations for calcium intakes during pregnancy and lactation differ around the world, reflecting the inadequacy of knowledge about calcium requirements in human reproduction. In theory, insufficient calcium supply during pregnancy and lactation could result in maternal bone loss, reduced breast-milk calcium secretion or impaired infant bone development. However, although calcium intakes vary widely, no specific problems associated with dietary calcium deficiency have been identified. Alterations in absorption, metabolism, and excretion may conserve calcium when requirements increase. Bone changes have been observed in pregnancy and lactation, but the relationship with diet is unknown. Similarly, the effects of maternal calcium intake on breast-milk calcium and infant bone growth are not understood. Calcium salts (1-2 g Ca/d) may reduce hypertensive disorders in pregnancy, but the role of dietary calcium needs exploration. More research is required before we can be confident about advising women to increase their calcium intakes during pregnancy and lactation.