Efficacy of daily and monthly high-dose calciferol in vitamin D-deficient nulliparous and lactating women

Background: We previously found a high prevalence of vitamin D deficiency and low medication regimen compliance in Arab and East Indian women residing in the United Arab Emirates (UAE). The appropriate dosing regimen for improving vitamin D status in this population is not known. Objective: We aimed to determine the efficacy of daily and monthly supplementation with vitamin D ₂, the only high-dose calciferol available in the UAE, in lactating and nulliparous women. Design: Healthy lactating (n = 90) and nulliparous (n = 88) women were randomly assigned to consume 2000 IU vitamin D₂/d or 60 000 IU vitamin D₂/mo for 3 mo. Serum 25-hydroxyvitamin D [25(OH)D] concentrations were measured by radioimmunoassay at baseline and every month. Results: Most women had vitamin D deficiency [ie, 25(OH)D < 50 nmol/L] at study entry. Mean ± SD 25(OH)D concentrations at 3 mo were significantly higher than baseline in both lactating (39.8 ± 12.4 and 25.2 ± 10.7 nmol/L, respectively) and nulliparous (40.4 ± 23.4 and 19.3 ± 12.2 nmol/L, respectively) women (P < 0.001 for both). In total, vitamin D supplementation was effective in achieving serum 25(OH)D concentrations of ≥50 nmol/L in 21 (30%) of 71 women at endpoint. Conclusions: Oral vitamin D₂ supplementation with 2000 IU/d or 60 000 IU/mo for 3 mo was safe, and it increased serum 25(OH)D concentrations significantly; however, only a small proportion of the women studied achieved concentrations of ≥50 nmol/L. This suggests that, when sunlight exposure is limited, doses of vitamin D ₂ higher than those currently studied may be needed. Monthly dosing appears to be a safe and effective alternative to daily dosing.