Based on the reports of a 2-year, randomized, double-dummy VERO trial, women with baseline 25(OH)D sufficiency and those with 25(OH)D insufficiency showed no notable difference in fracture risk reduction with Teriparatide versus Risedronate and the serum 25(OH)D levels reduces during Teriparatide treatment.

Postmenopausal females with osteoporosis obtained 35 mg oral Risedronate weekly or 20 μg subcutaneous Teriparatide daily along with concomitant 400–800 IU/day of vitamin D supplements and 500–1000 mg of elemental calcium. Predefined subgroups of 25(OH)D sufficient and insufficient patients used to assess the fracture endpoints. Logistic and Cox proportional hazards regression models were applied to investigate the heterogeneity of the treatment effect on fractures.

The levels of mean serum 25(OH)D among Teriparatide and Risedronate groups was 31.9 and 31.5 ng/mL, and 16.8% and 17.9% of patient were 25(OH)D insufficient, respectively. At month six, the patients of the Teriparatide group exhibited reduced mean serum 25(OH)D concentration; whereas, in the Risedronate group, it remained constant. The ratio of 25(OH)D insufficient patients at six months noticed in the Teriparatide, and Risedronate groups were 26.7% and 5.6%, respectively. With nonsignificant treatment by 25(OH)D interactions in all fracture investigations, no significant difference in the risk reduction for any of the fracture endpoints was noticed between subgroups by 25(OH)D sufficiency status at baseline. With the implementation of Teriparatide, a decline was seen the serum 25(OH)D concentrations.