VITAMIN D SUPPLEMENTATION, PARATHYROID HORMONE (PTH) AND PLASMA VITAMIN D RESPONSE AMONG MALAYSIAN FEMALE ADULTS: DOUBLE BLINDED, RANDOMISED CLINICAL TRIAL OF EFFICACY

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.