Taking vitamin D together with calcium has been found to reduce the risk of bone fractures while vitamin D alone was not.
The analysis of seven separate studies published in the British Medical Journal found that taking 10 micrograms of vitamin D together with calcium reduced the risk of overall fractures, as well as hip fractures.
The analysis of 68,517 participants with an average age of 69.9 years, however, did not find any reduction in fracture risk from vitamin D supplements alone, whether in 10 microgram or 20 microgram doses.
"Conflicting evidence exists on the role of vitamin D, either alone or in combination with calcium, in reducing fractures," Opinder Sahota, professor of orthogeriatric medicine at Queen's Medical Centre, Nottingham, UK, wrote in an accompanying editorial.
"Some studies have shown a reduction in the risk of fractures, others have shown no effect, and one recent study found an increased risk of hip fracture.
"The best dose to use, which patients benefit most, and which fractures are most amenable to such treatment remain a clinical dilemma.
"These findings are important because this is one of the few individual patient data analyses to show that vitamin D alone, irrespective of dose, does not reduce the risk of fracture.
"In contrast, it found that combined calcium and vitamin D reduced the overall risk of fracture, but that only low dose vitamin D with calcium reduced the risk of hip fracture."