Calcium

About Calcium

Calcium is the most abundant mineral in the body, with about 99 percent stored in bones and teeth as hydroxyapatite. Official recommended intakes vary by age, sex and life stage, and are higher for older adults. Blood calcium is held within a narrow range by parathyroid hormone, calcitonin and active vitamin D, and when dietary intake falls short the body draws on bone reserves, so chronic low intake contributes to bone loss and osteoporosis. Beyond its structural role, calcium ions act as a universal intracellular signal and are essential for muscle contraction, nerve transmission, blood clotting, hormone secretion and enzyme activation. Absorption is enhanced by vitamin D and inhibited by phytates in bran and oxalates in foods such as spinach, and absorption efficiency declines with age. The Womens Health Initiative found that calcium plus vitamin D supplements modestly improved hip bone density without clearly reducing overall fractures, and they increased kidney stone risk. Food sources include dairy products, sardines with bones, kale and fortified plant milks.