Development and Validation of a Vitamin D Status Prediction Model in Danish Pregnant Women: A Study of the Danish National Birth Cohort

Abstract

Vitamin D has been hypothesized to reduce risk of pregnancy complications such as preeclampsia, gestational diabetes mellitus, and preterm delivery. However, many of these outcomes are rare and require a large sample size to study, representing a challenge for cohorts with a limited number of preserved samples. The aims of this study were to (1) identify predictors of serum 25-hydroxy-vitamin D (25(OH)D) among pregnant women in a subsample (N = 1494) of the Danish National Birth Cohort (DNBC) and (2) develop and validate a score predicting 25(OH)D-status in order to explore associations between vitamin D and maternal and offspring health outcomes in the DNBC. In our study sample, 42.3% of the population had deficient levels of vitamin D (<50 nmol/L 25(OH)D) and average levels of 25(OH)D-status were 56.7(s.d. 24.6) nmol/L. A prediction model consisting of intake of vitamin D from diet and supplements, outdoor physical activity, tanning bed use, smoking, and month of blood draw explained 40.1% of the variance in 25(OH)D and mean measured 25(OH)D-level increased linearly by decile of predicted 25(OH)D-score. In total 32.2% of the women were placed in the same quintile by both measured and predicted 25(OH)D-values and 69.9% were placed in the same or adjacent quintile by both methods. Cohen's weighted kappa coefficient (Κ = 0.3) reflected fair agreement between measured 25(OH)D-levels and predicted 25(OH)D-score. These results are comparable to other settings in which vitamin D scores have shown similar associations with disease outcomes as measured 25(OH)D-levels. Our findings suggest that predicted 25(OH)D-scores may be a useful alternative to measured 25(OH)D for examining associations between vitamin D and disease outcomes in the DNBC cohort, but cannot substitute for measured 25(OH)D-levels for estimates of prevalence.

Vitamin D Status during Pregnancy in a Multi-Ethnic Population-Representative Swedish Cohort

“…Vitamin D deficiency among women born in Africa was also less common (50%) than previously indicated (90% among Swedish women born in Somalia) [15]. Risk factors for vitamin D deficiency (25(OH)D <30 nmol/L) in early pregnancy were in line with previous findings [13,17,27]. The determinants in the subgroup born in Africa and Asia were fewer, indicating less effect of season but could possibly also be explained by lower power due to a smaller group size.…”

“…These studies were of small sample size and not representative of the general pregnant population. Danish studies have found average concentrations between 57 and 76 nmol/L and that between 3% and 10% of pregnant women have 25(OH)D levels <25 nmol/L [16,17,18]. Findings from England indicate a mean 25(OH)D of 62 nmol/L [19], while Scottish data indicate a lower mean, 40 nmol/L [20].…”

Seasonal Epidemiology of Serum 25-Hydroxyvitamin D Concentrations among Healthy Adults Living in Rural and Urban Areas in Mongolia

“…The winter finding is likely the result of chance. UV monitoring may have provided more accurate measurements of sun-exposure duration, however our research also corroborates a need for more sensitive sun-exposure questionnaires, which may be less expensively administered in epidemiologic studies but which have as yet rarely succeeded in capturing more than 40% of variation in vitamin D status in other populations [25]. …”

Determinants of vitamin D status in pregnant women and neonates

“…In other observational studies, clinical trials examining women later in gestation, and the current study's examination of neonatal cord blood, significant differences over twice this magnitude have been found between supplement users and non-users. 3,7,8,17 In a recent clinical trial, a mean increase of 10.5 nmol/L from baseline (mean 14 weeks' gestation) to delivery was observed in pregnant women assigned to 400 IU/day. 21 Nevertheless, a substantial proportion of supplement users still have low vitamin D status.…”

“…4 Given the evidence suggesting a beneficial effect of vitamin D in pregnancy and fetal dependence on maternal 25(OH)D, it is important to determine which of these factors help to identify pregnant women at risk of low vitamin D status and to estimate the effect they could have on 25(OH)D levels to inform the nature of potential interventions. However, few large studies have been conducted, [6][7][8][9][10][11] and none were in Canada. Therefore, our objective in this study of over 1,500 pregnant Canadian women was to determine the association between maternal characteristics and vitamin D status.…”