Vitamin D and Bone: Take It or Break It Says New Study
Studies telling people to take enough vitamin D to help prevent fractures are nothing new, since it's well established that vitamin D is necessary for bone health. However, now a new meta-analysis has zoomed in on a key issue: it's not the amount of vitamin D people are assigned to take but the amount actually taken and regularly that matters. In other words, take it or break it (your bones, that is).
The problem with other vitamin D studies
People often have good intentions, which may be completely harmless in some situations, but not so when it concerns health issues, such as compliance in taking medications or supplements. For example, it's not uncommon for individuals to "intend" to take their vitamin D supplement or their blood pressure medication every day, but then they forget or procrastinate and miss doses.
According to the authors of the recent meta-analysis, reported in the July 5 issue of the New England Journal of Medicine, many previous studies and meta-analyses of vitamin D and bone health have tended to look at how much of the vitamin people were told to take rather than how much they actually took. The gap between intention and actual can be significant.
Therefore, the investigators, under direction of Heike Bischoff-Ferrari, MD, DrPH, of University Hospital in Zurich, evaluated only controlled studies of oral vitamin D use among individuals age 65 and older. The meta-analysis included 12 studies with a total participant level of 30,011.
The investigators found an insignificant 10 percent reduction in the risk of experiencing hip fracture and a significant 7 percent reduction in the risk of nonvertebral fracture when they did an intention-to-treat analysis; in other words, what the study subjects were told to take.
However, when they considered the amount of vitamin D the participants actually consumed, they found a 30 percent reduced risk of hip fracture among those who took the most vitamin D: 792 IU to 2,000 IU per day. Among this same group of participants who took the high doses of vitamin D, the investigators also saw a 14 percent reduced risk of nonvertebral fractures.
One factor that can have an impact on the effect of taking vitamin D supplements is a person's vitamin D level at the beginning of a study (baseline level). In fact, the authors noted that they had baseline levels of vitamin D (hydroxyvitamin D) for only 4,383 of the participants. However, they also pointed out that the results of this subgroups of subjects were similar to those of the entire study population.
Another factor in this meta-analysis is that all the subjects who were taking high amounts of vitamin D were also taking calcium. It's been well established that both calcium and vitamin D are necessary for bone health and helping reduce the risk of fracture.
One of the largest studies to come to this conclusion was DIPART (Vitamin D Individual Patient Analysis of Randomized Trials) group, which evaluated data from seven major randomized trials (68,517 participants) of vitamin D with calcium or vitamin D alone. The reviewers found that vitamin D alone (400-800 IU) was not effective in preventing fractures, but that calcium and vitamin D together reduced hip fractures and total fractures.
The take-home message from the current meta-analysis appears to be that vitamin D can help reduce the risk of fractures when individuals take a high amount (about 800 IU or more; the Institute of Medicine recommends 600 IU for adults up to age 70). The other message: you need to really take vitamin D for it to work: take it or break it.
Bischoff-Ferrari HE t al. A pooled analysis of vitamin D dose requirements for fracture prevention. N Engl J Med 2012; DOI:10.1056/NEJMoa1109617
DIPART (Vitamin D Individual Patient Analysis of Randomized Trials) Group. Patient level pooled analysis of 68,500 patients from seven major vitamin D fracture trials in US and Europe. BMJ 2010 Jan 12; 340:b5463
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