Table 1– Relative risks for self-reported respiratory symptoms and infections according to clinical serum 25-hydroxyvitamin D (25(OH)D) levels
Subjects n/N25(OH)Dp-value
<25 nmol·L−125–49 nmol·L−150–74 nmol·L−1≥75 nmol·L−1
0–6 months
 Subjects2025100 (4.9)666 (32.9)572 (28.2)687 (33.9)
 Wheezing525/20210.64 (0.44–0.95)0.72 (0.61–0.87)0.96 (0.81–1.15)Reference0.000
 Prolonged cough319/20190.33 (0.16–0.69)0.68 (0.53–0.88)0.80 (0.62–1.02)Reference0.000
 Croupy cough79/20240.13 (0.02–1.01)0.27 (0.14–0.53)0.68 (0.41–1.12)Reference0.000
 Diagnosed LRTI288/20210.45 (0.24–0.84)0.63 (0.49–0.81)0.76 (0.58–0.99)Reference0.000
 Diagnosed ear  infection123/20240.83 (0.41–1.69)0.64 (0.40–1.01)0.93 (0.61–1.93)Reference0.142
 Diarrhoea363/20240.99 (0.65–1.50)0.93 (0.73–1.18)1.05 (0.83–1.33)Reference0.484
 Vomiting215/20241.04 (0.60–1.81)0.86 (0.63–1.18)0.98 (0.71–1.35)Reference0.733
6–12 months
 Subjects194694 (4.8)628 (32.3)552 (28.4)672 (34.5)
 Wheezing601/19461.10 (0.80–1.52)1.21 (1.03–1.43)1.17 (0.98–1.39)Reference0.163
 Prolonged cough450/19451.09 (0.73–1.62)1.16 (0.95–1.42)1.09 (0.89–1.35)Reference0.196
 Croupy cough142/19461.62 (0.86–3.04)0.92 (0.62–1.36)0.87 (0.58–1.32)Reference0.773
 Diagnosed LRTI368/19461.11 (0.72–1.71)1.22 (0.97–1.54)1.12 (0.87–1.42)Reference0.155
 Diagnosed ear  infection386/19451.29 (0.87–1.92)1.13 (0.90–1.42)1.18 (0.93–1.48)Reference0.118
 Diarrhoea691/19440.91 (0.67–1.25)0.96 (0.83–1.12)1.00 (0.86–1.16)Reference0.670
 Vomiting415/19441.26 (0.85–1.88)1.18 (0.96–1.45)0.96 (0.76–1.20)Reference0.046
12–24 months
 Subjects187695 (5.1)601 (32.0)537 (28.6)643 (34.3)
 Wheezing484/18760.85 (0.58–1.25)1.01 (0.84–1.22)0.92 (0.75–1.12)Reference0.991
 Prolonged cough441/18750.82 (0.52–1.29)1.19 (0.97–1.45)1.07 (0.86–1.33)Reference0.328
 Croupy cough210/18760.79 (0.42–1.48)0.79 (0.58–1.08)0.76 (0.55–1.05)Reference0.288
 Diagnosed LRTI382/18750.69 (0.41–1.14)0.98 (0.79–1.22)0.92 (0.73–1.16)Reference0.929
 Diagnosed ear  infection506/18751.07 (0.77–1.50)0.95 (0.78–1.14)1.04 (0.86–1.25)Reference0.857
 Diarrhoea671/18751.23 (0.95–1.57)1.01 (0.87–1.18)0.96 (0.82–1.13)Reference0.680
 Vomiting467/18751.13 (0.79–1.61)1.07 (0.88–1.30)0.98 (0.80–1.20)Reference0.636
  • Data are presented as n, n (%) or relative risk (95% CI), unless otherwise stated. p-values were derived from Poisson regression analyses with the log-transformed 25(OH)D levels as a continuous variable. All analyses were adjusted for child’s sex, birthweight and gestational age, and for maternal age at childbirth, educational level, pre-pregnancy body mass index, parity, ethnicity, smoking in pregnancy and duration of breastfeeding. LRTI: lower respiratory tract infection.