To evaluate the relative benefits of calcium with or without vitamin D on bone health, Dr Richard Prince, at the University of Western Australia, Perth, assigned 120 women to take 1200 milligrams of calcium daily along with an inactive placebo pill or a vitamin D tablet, or two placebo tablets.

The women were between 70 and 80 years old. After 1 year, bone mineral density at the hip was preserved in the calcium group and the calcium+vitamin D group, but not in the double-placebo 'control' group.

However, at 3 and 5 years, only the group that got calcium plus vitamin D group maintained hip bone density, the investigators report in the Journal of Clinical Endocrinology and Metabolism.

They conclude that adequate levels of vitamin D are necessary for calcium to do its job in keeping bones healthy. --REUTERS