Vitamin D deficiency in early childhood: prevalent in the sunny South Pacific

OBJECTIVE: To estimate the prevalence of and risk factors for vitamin D deficiency in young urban children in Auckland, New Zealand, where there is no routine vitamin D supplementation. DESIGN: A random sample of urban children. Vitamin D deficiency was defined as serum 25-hydroxyvitamin D <27.5 nmol/l (<11 ng/ml). Logistic regression analysis was used to calculate odds ratios and, from these, relative risks (RR) and 95% confidence intervals were estimated. SETTING: Auckland, New Zealand (36 degrees 52'S), where the daily vitamin D production by solar irradiation varies between summer and winter at least 10-fold. SUBJECTS: Children aged 6 to 23 months enrolled from 1999 to 2002. RESULTS: Vitamin D deficiency was present in forty-six of 353 (10%; 95% CI 7, 13%). In a multivariate model there was an increased risk of vitamin D deficiency associated with measurement in winter or spring (RR = 7.24, 95% CI 1.55, 23.58), Pacific ethnicity (RR = 7.60, 95% CI 1.80, 20.11), not receiving any infant or follow-on formula (RR = 5.69, 95% CI 2.66, 10.16), not currently receiving vitamin supplements (RR = 5.32, 95% CI 2.04, 11.85) and living in a more crowded household (RR = 2.36, 95% CI 1.04, 4.88). CONCLUSIONS: Vitamin D deficiency is prevalent in early childhood in New Zealand. Prevalence varies with season and ethnicity. Dietary factors are important determinants of vitamin D status in this age group. Vitamin D supplementation should be considered as part of New Zealand's child health policy.