Men's Osteoporosis Support Group
How much vitamin D to take?
Osteoporos Int. 2011 Sep 10. [Epub ahead of print]. The effect of high-dose vitamin D on bone mineral density and bone turnover markers in postmenopausal women with low bone mass-a randomized controlled 1-year trial. Grimnes G and others. PMID: 21909730. This 1-year study involved 297 women aged 50-80 who took either 800 IU vitamin D3 per day or the equivalent of 6,500 IU/day. All women also took 1000 mg elemental calcium/day. Total hip and lumbar spine bone mineral density (BMD) was done at baseline and after one year, and bone turnover markers were also tested.
Note that most standards consider 70 nmol/l to be adequate vitamin D, meaning the women were vitamin D replete going into the study. Thus the study was testing to see if additional vitamin D beyond the normal range would improve the BMD and bone turnover parameters that were tested.
The results showed that in the high-dose group serum vitamin D increased from a mean of 71 nmol/l to 185 nmol/l. In low-dose group it increased from a mean of 71 nmol/l to 89 nmol/l. There was no significant change in BMD in either group. Bone turnover was reduced in both groups, but more so in the standard-dose group for the bone formation marker P1NP. The authors concluded this means the standard-dose treatment was more efficient. The study concluded, “One year treatment with 6,500 IU vitamin D(3)/day was not better than 800 IU/day regarding BMD in vitamin D-replete postmenopausal women with reduced bone mass and was less efficient in reducing bone turnover.”
Editor's comments. These results are interesting and imply that more vitamin D, if testing shows serum vitamin D levels are in the normal range, doesn't appear to help improve BMD or bone turnover markers. The Osteoporosis Issues article concerning vitamin D notes that several studies show correlation between serum vitamin D levels and several types of cancer, so there might be other reasons to maintain a high serum vitamin D level. Further research will hopefully clarify these issues.
This was only a one-year study, and there were some non-significant improvements in BMD during the study. Perhaps longer studies would demonstrate even greater improvements in BMD that might reach statistical significance by increased vitamin D intake even if testing shows normal serum levels before starting the high-dose vitamin D.
Bottom line. These results show little reason to take high doses of vitamin D if your serum vitamin D is in the normal range if the goal is to improve BMD or bone turnover markers. The most important finding that I see would be to have your serum vitamin D level tested occasionally to be sure it is in the normal range. Unless further studies show some reason to increase it above the normal range, there appears to be no reason to do so to improve BMD.