An investigation of the association between maternal body weight and vitamin D status during pregnancy

  • Raghad Alhomaid

Student thesis: Doctoral Thesis

Abstract

The combined effects of maternal obesity and low vitamin D status have adverse implications for maternal and fetal health. The overall aim of this PhD thesis was to investigate the association between maternal body weight and vitamin D status throughout pregnancy. From the systematic review, this thesis reports that few observational studies have assessed vitamin D status across BMI categories. Obese or obese class 2 pregnant women had lower vitamin D status compared to non-obese pregnant women. Maternal vitamin D status was negatively associated with maternal BMI and positively associated with infants vitamin D status. Vitamin D status was lower in infants born to obese mothers than infants born to normal weight mothers. When we examined data from a previous cohort of pregnant women in Northern Ireland (from 2006) who were not taking vitamin D supplements in pregnancy, we were able to examine the true association between BMI and vitamin D status in this unique cohort. Our results demonstrate that pregnant women with obesity had significantly lower vitamin D status than those who were normal weight, this was evident particularly during the winter months. There was a high prevalence of vitamin D insufficiency (<50 nmol/L) among pregnant women living in Northern Ireland in 2006. When we assessed the association between BMI and vitamin D status in early pregnancy in a cohort that were recruited for the purposes of this PhD work, we found that pregnant women with overweight and obesity had significantly lower vitamin D status compared to pregnant women of normal weight in early pregnancy despite 62% of women reporting to take a vitamin D supplement. Maternal BMI was found to be a significant negative predictor of vitamin D status and a high prevalence of vitamin D insufficiency still exists among pregnant women living in Northern Ireland in 2017. This insufficiency was highest among non-supplement users during winter months. We assessed the effect of supplementation with 10μg vs 20μg vitamin D3/d throughout pregnancy on vitamin D status of normal weight, overweight and obese pregnant women and on the cord blood of their infants. We report that vitamin D status increased throughout the pregnancy in both treatment groups, with a significantly higher increase observed in the 20µg group. In the 20µg group, maternal and cord vitamin D status reached and maintained sufficiency (≥50 nmol/L) throughout pregnancy, even in those who started pregnancy with an insufficient status. In obese women who started pregnancy with an insufficient vitamin D status, the related cord blood vitamin D status was deficient (<25 nmol/L) in both treatment groups (4). Overall, maternal obesity was negatively associated with maternal and infant vitamin D status and the current recommendation of 10µg/d is inadequate to reach and maintain sufficiency in those who start pregnancy with an insufficient status.
Date of AwardJul 2018
Original languageEnglish
SponsorsRoyal Embassy of Saudi Arabia
SupervisorMaria Mulhern (Supervisor) & Mary Mc Cann (Supervisor)

Keywords

  • Maternal obesity
  • Pregnancy
  • Vitamin D
  • Body mass index

Cite this

An investigation of the association between maternal body weight and vitamin D status during pregnancy
Alhomaid, R. (Author). Jul 2018

Student thesis: Doctoral Thesis