#374 Vitamin D and Fracture Prevention: Not what it’s cracked up to be?
CLINICAL QUESTION
Does vitamin D prevent fragility fractures?
BOTTOM LINE
Vitamin D alone does not prevent fractures regardless of dose, vitamin D status or previous fracture. The combination of calcium and vitamin D might reduce the risk of total fractures from 11.5% to 10.9% and hip fractures from 1.8% to 1.5% over 9-84 months, but this benefit may be limited to women in long-term care. Adding calcium increases risk of renal calculi (2.1% to 2.5%).
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EVIDENCE
- Eight systematic reviews1-8 of 7-36 randomized controlled trials (RCTs); 34,000-76,000 mostly community-dwelling women: some with previous fracture, established osteoporosis or metabolic bone disease, followed 9-84 months.
- Vitamin D versus placebo/no treatment:
- Total fracture:1-8 No difference.
- Hip fracture:1-5,8 No difference. One systematic review7 (varying high doses) suggested slightly higher risk in women (1.2% versus 0.9%).
- Total or hip fractures:
- High dose (>800 IU): Three systematic reviews1,4,8 showed no difference, one7 showed increased risk (described above) and one6 showed benefit, but no absolute numbers reported.
- Baseline vitamin D level <50 nmol/L1 or previous fracture:2 No difference.
- Vitamin D-calcium combination versus placebo:
- Total fracture: 10.9% versus 11.5% (placebo), number needed to treat (NNT)=167.2 Others showed similar.3,5,6 One systematic review did not report largest RCT.1
- Removing two RCTs of women in long-term care: Results no longer statistically different.2
- Hip fracture:25% versus 1.8% (placebo), NNT=333.
- Two systematic reviews found similar; 3,5 one found no difference.8
- Total or hip fracture:
- Baseline vitamin D <50 nmol/L1 or previous fracture:1,2 No difference.
- Total fracture: 10.9% versus 11.5% (placebo), number needed to treat (NNT)=167.2 Others showed similar.3,5,6 One systematic review did not report largest RCT.1
- Adverse events:
- Vitamin D alone: None.2
- Combination: No difference in mortality or gastrointestinal effects;2 renal calculi increased (2.5% versus 2.1% placebo).7
- Limitations: Disproportionate number of smaller positive studies, skewing results towards favouring vitamin D.2,4 Randomization process and concealment uncertain.2
CONTEXT
- Calcium alone has no effect on the risk of total or hip fracture.1,8
- Osteoporosis Canada: Supplementation with vitamin D and calcium is unlikely to have clinically important benefit if diet contains adequate calcium.9
- Measuring vitamin D levels routinely is unnecessary. No RCTs have evaluated treating to a target vitamin D level to prevent fractures.10
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