Researchers Examine Optimal Vitamin D Dose for Osteoporosis

Even though vitamin D is quite frequently used to treat osteoporosis, the medical community does not know its optimal dose.
The standard dose is 800 IU/day, but is that the most effective dose?  In 2011, researchers from Norway published an article in Osteoporosis International (the online version appeared September 10, 2011) on their vitamin D study—which centered around the question “Does a daily dose of 6,500 IU of vitamin D3 improve bone mineral density in the hip and spine when compared to a daily dose of 800 IU?”

The study, which was a 1-year randomized double-blind controlled trial, involved 297 postmenopausal women with a bone mineral density (BMD) T-score ≤-2.0 in either the lumbar spine (L2-L4) or total hip.  The women were randomized to 6,500 IU vitamin D3/day (20,000 IU twice/week + 800 IU/day) or 800 IU vitamin D3/day (placebo twice/week + 800 IU/day).  Women in both groups received 1,000 mg elemental calcium every day.

The primary endpoint of the study was a change in BMD in lumbar spine and total hip.

At the end of the study, serum 25-hydroxyvitamin D (25(OH)D) was measured in both groups.  In the high-dose group, 25(OH)D increased [mean (SD)] from 71 (23) to 185 (34) nmol/L.  In the standard-dose group, 25(OH)D increased [mean (SD)] from 71 (22) to 89 (17) nmol/L.

BMD in lumbar spine and total hip was unchanged or slightly improved; there were no significant differences between the dose groups.

Bone turnover was reduced in both groups.  However, the standard-dose group showed a more pronounced reduction in serum levels of P1NP, a bone formation marker; this may indicate that this treatment was more efficient.

Between the groups, there was no difference in adverse events.

The researchers concluded in this study that 1-year treatment with 6,500 IU/day of vitamin D3 was not better than 800 IU/day in terms of BMD in vitamin D-replete postmenopausal women with reduced bone mass.  The higher dose was less efficient in reducing bone turnover.