36,282 women aged 50 to 79 years old were recruited to this study from the Women's Health Initiative (WHI). They were randomised to Calcium and Vitamin D or placebo and followed up for 7 years. Data were collected on fracture events. A sub-group of 2,431 had bone mineral density (BMD) assessments periodically.
Despite a statistically significant rise in BMD in the group receiving Calcium and Vitamin D there was no difference in the rate of hip fractures or all fractures. A benefit was apparent in those patients who continued to take the medication and in 'higher risk' patients although women in the active arm of the study also had a greater risk of kidney stones.
There were confounders in this study; the fracture rate in the placebo arm was half the expected number, 24% stopped the study medication, only 59% were taking more than 4 in 5 doses and the dose of Vitamin D was inadequate by current standards (400IU per day rather than 800IU per day).
Action: Calcium and Vitamin D supplementation may be unsuitable for otherwise healthy postmenopausal women if fracture prevention is the aim of treatment. In women at higher risk of fractures supplementation has a positive effect and should be offered as part of a comprehensive treatment plan.
- Women's Health Initiative Investigators. Calcium plus Vitamin D Supplementation and the Risk of Fractures. NEJM 2006;354:669-83