TABLE 1

Characteristics of 922 Participants According to Cord-Blood Levels of 25(OH)D

CharacteristicSerum 25(OH)D ConcentrationP for Trenda
≥75 nmol/L25–74 nmol/L<25 nmol/L
25(OH)D, median (IQR), nmol/L100 (87–124)41 (34–53)19 (14–22)
n251491180
Season of birth, %
    Spring (September to November)193633
    Summer (December to February)40124
    Fall (March to May)33199
    Winter (June to August)93353<.001
Study site, %
    Wellington535246
    Christchurch474854.18
Parents and household
Maternal age at birth, mean (SD), y31 (5)30 (5)29 (5)<.001
New Zealand Deprivation Index, mean (SD)4.4 (2.8)4.8 (2.9)5.3 (3.0).002
Maternal history of asthma, %252627.72
Paternal history of asthma, %152325.009
Newborn and home environment
Gestational age at birth, median (IQR), wk40 (39–41)40 (39–40)40 (39–41).01
Male, %515246.38
Child's ethnicity, %
    European837463<.001
    Māori121616
    Pacific Islander3612
    Other358
Any smoking during pregnancy, %172126.03
Any passive smoke exposure at 3 mo of age, %263538.008
No. of children aged <16 y in the household when the child was 3 mo old, mean (SD)0.8 (0.9)0.7 (0.9)0.8 (1.0).97
Endotoxin on the bedroom floor when the child was 3 mo old, mean (SD), log EU/g9.1 (2.1)9.1 (2.1)9.2 (1.9).60
Damp, musty smell in any room when the child was 3 mo old, %413741.99
Duration of exclusive breastfeeding, mean (SD), mo2.2 (2.0)2.0 (2.0)1.8 (1.9).06
Potential intermediate factors
    Birth weight, mean (SD), kg3.6 (0.5)3.6 (0.5)3.6 (0.5).27
    Skin-prick test positivity at 15 mo of age, %263223.64
  • a P for trend is based on linear regression or the Kruskal-Wallis test for continuous variables and a nonparametric test for trend based on the Wilcoxon-Mann-Whitney test for categorical variables (for season of birth, we tested winter trend; for ethnicity, we tested European trend).