The same annual dose of 292000 IU of vitamin D3 (cholecalciferol) on either daily or four monthly basis for elderly women: 1-year comparative study of the effects on serum 25(OH)D3 concentrations and renal function

P>Objective Daily dosing of vitamin D supplements may be difficult among older people. Infrequent administration of 'megadoses' controlled by health care personnel may overcome adherence problem. We compared the efficacy and safety of two oral dosages (800 IU daily or 97333 IU four monthly) of vitamin D-3 resulting in the equal annual dose of 292000 IU. Design Randomized, double-blind, double-dummy parallel group comparison. Patients Forty women aged 69 center dot 3-78 center dot 8 years. Interventions Vitamin D-3 400 IU twice daily (D group) or vitamin D-3 oil 97333 IU every 4 months (4 M group) for 1 year. All received 1 g of calcium daily. Measurements Serum 25-hydroxyvitamin D-3 [25(OH)D-3] in relation to the target levels of 50-75 nmol/l, PTH, serum type I procollagen aminoterminal propeptide (PINP), serum and urine calcium, renal function. Results A quantity of 25OHD(3) increased more in D group than in 4 M group (P < 0 center dot 0001). All participants in D group and 67% in 4 M group had 25(OH)D-3 above 50 nmol/l at 12 months; the target level of 75 nmol/l was reached by 47% and 28% respectively. PTH did not show any seasonal perturbation in either group. PINP declined and urinary calcium rose similarly in the study groups over time (P < 0 center dot 0001). Renal function did not worsen in either group. Conclusions In terms of serum 25(OH)D-3 concentrations, 800 IU daily was more efficient than a 97333 IU every 4 months. However, to increase adherence, the latter is still worth developing. Both treatments increased urinary excretion of calcium, but did not worsen renal function.