We thank the midwives in Wellington, Porirua and Canterbury for their assistance with recruitment, and all the families and children for their participation. The New Zealand Asthma and Allergy Cohort Study Group consisted of J. C., M. Duignan, M. J. E., D. Fishwick, P. Fitzharris, T. I., V. Irvine, R. Kelly, P. Lampshire, J. Lane, P. Leadbitter, C. MacDonald, F. McCartin, S. McLeod, A. Nicholson, P. Pattemore, K. Roff, G. Sawyer, R. Siebers, G. I. T., K. W., H. Wilson and K. Withell. This work was supported by grants from the Health Research Council of New Zealand, the David and Cassie Anderson Bequest (Wellington, New Zealand), and the Massachusetts General Hospital Center for D-receptor Activation Research (Boston, MA, USA). None of the authors has any potential conflicts of interest. The authors' contributions are as follows: C. A. C. had full access to all the data in the study, and takes responsibility for the integrity of the data and the accuracy of the data analysis. C. A. C., G. I. T. and J. C. were involved in the study concept and design. C. A. C., T. I., K. W., R. I. T., M. J. E., G. I. T. and J. C. were involved in the acquisition of data. C. A. C., T. I., K. W., K. M. S., J. A. E. and J. C. were involved in the analysis and interpretation of data. C. A. C. was involved in the preparation of the manuscript. The critical revision of the manuscript for important intellectual content was done by C. A. C., T. I., K. W., R. I. T., K. M. S., M. J. E., G. I. T., J. A. E. and J. C. C.; A. C. and J. A. E. performed the statistical analysis. C. A. C., M. J. E. and J. C. were involved in the study supervision.
2 Hollis, BW & Wagner, CL (2004) Assessment of dietary vitamin D requirements during pregnancy and lactation. Am J Clin Nutr 79, 717–726.
3 Holick, MF (2007) Vitamin D deficiency. N Engl J Med 357, 266–281.
4 Javaid, MK, Crozier, SR, Harvey, NC, et al. (2006) Maternal vitamin D status during pregnancy and childhood bone mass at age 9 years: a longitudinal study. Lancet 367, 36–43.
5 Hypponen, E, Laara, E, Reunanen, A, et al. (2001) Intake of vitamin D and risk of type 1 diabetes: a birth-cohort study. Lancet 358, 1500–1503.
6 Camargo, CA Jr, Rifas-Shiman, SL, Litonjua, AA, et al. (2007) Maternal intake of vitamin D during pregnancy and risk of recurrent wheeze in children at 3 y of age. Am J Clin Nutr 85, 788–795.
7 Devereux, G, Litonjua, AA, Turner, SW, et al. (2007) Maternal vitamin D intake during pregnancy and early childhood wheezing. Am J Clin Nutr 85, 853–859.
8 Standing Committee on the Scientific Evaluation of Dietary Reference Intakes (1997) Dietary Reference Intakes for Calcium, Phosphorus, Magnesium, Vitamin D, and Fluoride. Washington, DC: Institute of Medicine.
9 Canadian Paediatric Society (2007) Vitamin D supplementation: recommendations for Canadian mothers and infants (Position Statement FNIM 2007-01). Paediatr Child Health 12, 583–589.
10 World Health Organization (2001) GLOBOCAN: Cancer Incidence, Mortality and Prevalence Worldwide, IARC Cancerbase No. 5, Version 1.0. Lyon: IARC.
11 Allan, W, Riedel, K, McKenzie, R, et al. (2009) Atmosphere – ozone and ultraviolet radiation. In Te Ara – Encyclopedia of New Zealand. http://www.TeAra.govt.nz/en/atmosphere/4 (accessed 11 January 2009).
12 Ministry of Health (2005) Food and Nutrition Guidelines for Healthy Pregnant and Breastfeeding Women: A Background Paper: Draft for Consultation. Wellington: Ministry of Health.
13 Watson, PE & McDonald, B (1999) Nutrition During Pregnancy: A Report to the Ministry of Health. Auckland: Massey University (Albany Campus).
14 Grant, CC, Wall, CR, Crengle, S, et al. (2009) Vitamin D deficiency in early childhood: prevalent in the sunny South Pacific. Public Health Nutr 12, 1893–1901.
15 Epton, MJ, Town, GI, Ingham, T, et al. (2007) The New Zealand Asthma and Allergy Cohort Study (NZA2CS): assembly, demographics and investigations. BMC Public Health 7, 26.
16 Salmond, C & Crampton, P (2001) NZDep2001 Index of Deprivation, User's Manual. Wellington: Department of Public Health, Wellington School of Medicine and Health Sciences.
17 Hanley, DA & Davison, KS (2005) Vitamin D insufficiency in North America. J Nutr 135, 332–337.
18 Rockell, JE, Green, TJ, Skeaff, CM, et al. (2005) Season and ethnicity are determinants of serum 25-hydroxyvitamin D concentrations in New Zealand children aged 5–14 y. J Nutr 135, 2602–2608.
19 Brot, C, Vestergaard, P, Kolthoff, N, et al. (2001) Vitamin D status and its adequacy in healthy Danish perimenopausal women: relationships to dietary intake, sun exposure and serum parathyroid hormone. Br J Nutr 86, Suppl. 1, S97–103.
20 Sachan, A, Gupta, R, Das, V, et al. (2005) High prevalence of vitamin D deficiency among pregnant women and their newborns in northern India. Am J Clin Nutr 81, 1060–1064.
21 Maghbooli, Z, Hossein-Nezhad, A, Shafaei, AR, et al. (2007) Vitamin D status in mothers and their newborns in Iran. BMC Pregnancy Childbirth 7, 1.
22 Bowyer, L, Catling-Paull, C, Diamond, T, et al. (2009) Vitamin D, PTH and calcium levels in pregnant women and their neonates. Clin Endocrinol (Oxf) 70, 372–377.
23 Bodnar, LM, Simhan, HN, Powers, RW, et al. (2007) High prevalence of vitamin D insufficiency in black and white pregnant women residing in the northern United States and their neonates. J Nutr 137, 447–452.
24 Lee, JM, Smith, JR, Philipp, BL, et al. (2007) Vitamin D deficiency in a healthy group of mothers and newborn infants. Clin Pediatr (Phila) 46, 42–44.
25 Nicolaidou, P, Hatzistamatiou, Z, Papadopoulou, A, et al. (2006) Low vitamin D status in mother–newborn pairs in Greece. Calcif Tissue Int 78, 337–342.
26 Wjst, M (2006) The vitamin D slant on allergy. Pediatr Allergy Immunol 17, 477–483.
27 Chen, TC, Chimeh, F, Lu, Z, et al. (2007) Factors that influence the cutaneous synthesis and dietary sources of vitamin D. Arch Biochem Biophys 460, 213–217.
28 Maghbooli, Z, Hossein-Nezhad, A, Karimi, F, et al. (2008) Correlation between vitamin D3 deficiency and insulin resistance in pregnancy. Diabetes Metab Res Rev 24, 27–32.
29 Erkkola, M, Kaila, M, Nwaru, BI, et al. (2009) Maternal vitamin D intake during pregnancy is inversely associated with asthma and allergic rhinitis in 5-year-old children. Clin Exp Allergy 39, 875–882.
30 Sidbury, R, Sullivan, AF, Thadhani, RI, et al. (2008) Randomized trial of vitamin D supplementation for winter-related atopic dermatitis in Boston: a pilot study. Br J Dermatol 159, 245–247.
31 Hillman, LS & Haddad, JG (1974) Human perinatal vitamin D metabolism. I. 25-Hydroxyvitamin D in maternal and cord blood. J Pediatr 84, 742–749.
32 Rifas-Shiman, SL, Rich-Edwards, JW, Willett, WC, et al. (2006) Changes in dietary intake from the first to the second trimester of pregnancy. Paediatr Perinat Epidemiol 20, 35–42.