Abstract:
Vitamin D insufficiency is a widespread phenomenon globally, affecting all
ages. In Malaysia, despite being a tropical country, there are increasing
reports of vitamin D insufficiency among women. Vitamin D intake
adequacy in child-bearing age women is important for reproductive health
including in fertility, conception and birth outcomes. In line with
international guidelines, the Malaysian recommended nutrient intake for
vitamin D is 600 IU/day. However, the efficacy of the recommended
vitamin D intake for healthy child-bearing age women to achieve sufficient
plasma 25-hydroxyvitamin D [25(OH)D] levels (≥50 nmol/L) is currently
unknown. This study aimed to investigate the efficacy of a 16 weeks
vitamin D supplementation on plasma 25(OH)D and intact parathyroid
hormone (PTH) concentrations in Malaysian women of child-bearing age.
In this double blind, randomised controlled trial, 106 healthy women aged
20-45 years were randomised into four groups receiving daily 500 mg of
calcium with either 0, 600 IU, 1200 IU or 4000 IU vitamin D supplement
for 16 weeks. Questionnaires and anthropometric measurements were
collected at baseline and post 16 weeks supplementation trial. Primary
outcomes were plasma 25(OH)D and intact PTH measured at baseline and post 16 weeks trial. Baseline characteristics, including anthropometric
status, sun exposure, vitamin D intake, plasma 25(OH)D and intact PTH did not differ significantly between groups (p > 0.03). Half of the participants showed vitamin D deficiency (25(OH)D <30 nmol/L), while another 40% were in the insufficiency category (25(OH)D 30-49 nmol/L) at baseline. After 16 weeks of supplementation, mean plasma 25(OH)D concentrations increased significantly (p < 0.03) among the test groups in a dose-dependent manner, with the group receiving 4000 IU/day vitamin D showing the highest increase (p < 0.03). About 30% of the women receiving 4000 IU/day vitamin D attained plasma 25(OH)D sufficiency level by 16 weeks of supplementation. Plasma intact PTH showed no significant changes between baseline and post-supplementation in the test groups (p > 0.03). General linear model revealed a significant correlation between plasma 25(OH)D concentration and skin colour tone (F = 9.064, p = <0.001). No significant association was observed between plasma intact PTH and key covariates, namely sun exposure, dietary vitamin D intake and body mass index.
In conclusion, vitamin D supplementation of 4000 IU/day, compared
to 600 IU and 1200 IU/day, showed the highest efficacy for increasing
plasma 25(OH)D levels among women of child-bearing age. There was no
obvious suppression in plasma intact PTH with vitamin D supplementation.
Further investigations are recommended for a better understanding of the
inverse relationship between plasma 25(OH)D and PTH levels in childbearing age women.
