A report in this week's edition of The Lancet sheds new light on that question.
That protection rate doubles when calcium supplements are taken correctly, report the researchers, who included Benjamin Tang, MD, of the Centre for Complementary Medicine Research at Australia's University of Western Sydney.
"For best therapeutic effect, we recommend minimum doses of 1200 milligrams [mg] of calcium, and 800 IU [international units] of vitamin D (for combined calcium plus vitamin D supplementation)," Tang's team writes.
Tang and colleagues reviewed 29 studies on the use of calcium supplements and vitamin D supplements in people aged 50 and older. Together, the studies included nearly 64,000 people who were almost 68 years old, on average.
Participants were followed for 3.5 years, on average.
During that time, people who took calcium supplements were not only less likely to fracture their bones, they also slightly reduced their rate of bone loss from their hip and spine, compared with people who didn't take calcium supplements.
Taking vitamin D supplements along with calcium supplements didn't budge the numbers much. But that may be because few studies used higher doses of vitamin D, according to the report.
People aged 70 and older, those who didn't get much calcium from their diets, thin people, and those at high risk of bone fractures were particularly likely to benefit from taking calcium supplements.
Weight-bearing exercise, which helps strengthen bones, wasn't covered in the study.