What you need to know about calcium

Calcium is billed as the bone-building nutrient. But some experts argue that we should pay more attention to exercise and vitamin D.

Starting on your 51st birthday, current government guidelines say you're supposed to consume 1,200 milligrams (mg) of calcium daily. With advancing years, both men and women begin to experience a decline in the density of bones that makes them weaker and more likely to break. In essence, your bone becomes more porous, and calcium supposedly fills in the holes.

But the amount of calcium adults need continues to be debated. The critics say there's little evidence that high intake has more than a marginal effect on bone density and fracture prevention. They say exercise and reversing vitamin D deficiency are not promoted enough and are more important for bone health. Professor Walter Willett, chair of the nutrition department at the Harvard School of Public Health, is one of the leading lights in the critical camp.