Background/objectives: Middle Eastern female immigrants are at an increased risk of vitamin D deficiency and their response to prescribed vitamin D dosages may not be adequate and affected by other factors. The objectives were to determine vitamin D deficiency and its determinants in Middle Eastern women living in Auckland, New Zealand (Part-I), and to determine serum 25-hydroxyvitamin D (serum-25(OH)D) response to two prescribed vitamin D dosages (Part-II) in this population.
Participants/methods: Women aged ⩾20 (n=43) participated in a cross-sectional pilot study during winter (Part-I). In Part-II, women aged 20-50 years (n=62) participated in a randomised, double-blind placebo-controlled trial consuming monthly either 50,000, 100,000 IU vitamin D3 or placebo for 6 months (winter to summer).
Results: All women in Part-I and 60% women in Part-II had serum-25(OH)D<50 nmol/l. Serum-25(OH)D was higher in prescribed vitamin D users than nonusers (P=0.001) and in Iranians than Arab women (P=0.001; Part-I). Mean (s.d.) serum-25(OH)D increased in all groups (time effect, P<0.001) and differed between groups (time × dosage interaction, P<0.001; 50,000 IU: from 44.0±16.0 to 70.0±15.0 nmol/l; 100,000 IU: 48.0±11.0 to 82.0±17.0 nmol/l; placebo: 45.0±18.0 to 54.0±18.0 nmol/l). Only 32% and 67% achieved serum-25(OH)D⩾75 nmol/l with 50,000 and 100,000 IU/month, respectively. Predictors of 6-month change in serum-25(OH)D were dose (B-coefficient±s.e.; 14.1±2.4, P<0.001), baseline serum-25(OH)D (-0.6±0.1, P<0.001) and body fat percentage (-0.7±0.3, P=0.01).
Conclusions: Vitamin D deficiency/insufficiency is highly prevalent in this population. Monthly 100,000 IU vitamin D for 6 months is more effective than 50,000 IU in achieving serum-25(OH)D ⩾75 nmol/l; however, a third of women still did not achieve these levels.