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 69.3-78.8 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 < 0.0001). 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 < 0.0001). 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.