The study, published online ahead of print in the Journal of Clinical Endocrinology & Metabolism, found that calcium therapy alone may be successful at preventing bone loss initially but was no different from using a placebo in preventing bone loss after three to five years.

"In the long-term, calcium alone loses its effectiveness in preventing bone loss, but there is good news," study author Richard Prince, of the University of Western Australia in Perth said in a statement. "Our five-year study has shown that a combination of calcium and vitamin D prevented bone loss for the duration of the study."

Prince and fellow researchers evaluated the relative benefits of five years of calcium supplementation with or without vitamin D2 compared to placebo on hip bone mineral density and bone related biochemistry in ambulatory elderly women ages 70 to 80 years.

The study found the combination of 1,200 mg of calcium a day and vitamin D 1,000 IU maintained hip bone mineral density constant for five years, while calcium alone was no different than the placebo after three to five years.