Childhood pneumonia in New Zealand.

While deaths from pneumonia during childhood in New Zealand (NZ) are now infrequent, childhood pneumonia remains a significant cause of morbidity. In this viewpoint, we describe pneumonia epidemiology in NZ and identify modifiable risk factors. During recent decades, pneumonia hospitalisation rates decreased, attributable in part to inclusion of pneumococcal conjugate vaccine in NZ's immunisation schedule. Irrespective of these decreases, pneumonia hospitalisation rates are four times higher for Pacific and 60% higher for Maori compared with children of other ethnic groups. Consistent with other developed countries, hospitalisation rates for pneumonia with pleural empyema increased in NZ during the 2000s. Numerous factors contribute to childhood pneumonia acquisition, hospitalisation and morbidity in NZ include poor quality living environments, malnutrition during pregnancy and early childhood, incomplete and delayed vaccination during pregnancy and childhood and variable primary and secondary care management. To reduce childhood pneumonia disease burden, interventions should focus on addressing modifiable risk factors for pneumonia. These include using non-polluting forms of household heating; decreasing cigarette smoke exposure; reducing household acute respiratory infection transmission; improving dietary nutritional content and nutrition during pregnancy and early childhood; breastfeeding promotion; vaccination during pregnancy and childhood and improving the quality of and decreasing the variance in primary and secondary care management of pneumonia.

An index measuring adherence to New Zealand Infant Feeding Guidelines has convergent validity with maternal socio-demographic and health behaviours and with children's body size.

Using data from a nationally generalisable birth cohort, we aimed to: (i) describe the cohort's adherence to national evidence-based dietary guidelines using an Infant Feeding Index (IFI) and (ii) assess the IFI's convergent construct validity, by exploring associations with antenatal maternal socio-demographic and health behaviours and with child overweight/obesity and central adiposity at age 54 months. Data were from the Growing Up in New Zealand cohort (n 6343). The IFI scores ranged from zero to twelve points, with twelve representing full adherence to the guidelines. Overweight/obesity was defined by BMI-for-age (based on the WHO Growth Standards). Central adiposity was defined as waist-to-height ratio > 90th percentile. Associations were tested using multiple linear regression and Poisson regression with robust variance (risk ratios, 95 % CI). Mean IFI score was 8·2 (sd 2·1). Maternal characteristics explained 29·1 % of variation in the IFI score. Maternal age, education and smoking had the strongest independent relationships with IFI scores. Compared with children in the highest IFI tertile, girls in the lowest and middle tertiles were more likely to be overweight/obese (1·46, 1·03, 2·06 and 1·56, 1·09, 2·23, respectively) and boys in the lowest tertile were more likely to have central adiposity (1·53, 1·02, 2·30) at age 54 months. Most infants fell short of meeting national Infant Feeding Guidelines. The associations between IFI score and maternal characteristics, and children's overweight/obesity/central adiposity, were in the expected directions and confirm the IFI's convergent construct validity.

Multimorbidity in Early Childhood and Socioeconomic Disadvantage: Findings From a Large New Zealand Child Cohort.

OBJECTIVE: In contrast with multimorbidity during adulthood, the relationship of childhood multimorbidity with socioeconomic position (SEP) is poorly understood. We aimed to describe early childhood multimorbidity and investigate the relationship of this with SEP. METHODS: Within a diverse prospective child cohort study, we determined associations of SEP with multimorbidity (defined as the presence of 2 or more chronic conditions) at age 2 years. Maternal SEP was ranked into 5 categories using an index constructed from variables collected antenatally describing maternal education, employment, financial stress, beneficiary status, housing tenure, overcrowding, and residential mobility. Missing values were handled using multiple imputation with chained equations. Independent associations of SEP with multimorbidity were described using adjusted odds ratios (OR) and 95% confidence intervals (CI). RESULTS: Of the 6822 women and 6853 children who were enrolled into the cohort study, 5737 (84%) mother-child dyads had complete antenatal data and were interviewed at age 2 years. Of these 5737, for 3826 (67%) dyads, there were complete data for all variables. Multimorbidity was present in 374/3838 (9.7%) of the cohort children. After multiple imputation and adjustment for maternal ethnicity, smoking, poor health, depressive symptoms, and child gender, the odds of multimorbidity being present were increased for children of mothers in the most (OR 1.74, 95% CI 1.16-2.59) and second most (OR 1.43, 95% CI 1.00-2.04) versus the least disadvantaged group. CONCLUSION: The odds of multimorbidity are increased for children whose mothers have lower SEP. Cumulative socioeconomic disadvantage increases the potential for a chronic illness trajectory to develop in early childhood.

Compared with Cow Milk, a Growing-Up Milk Increases Vitamin D and Iron Status in Healthy Children at 2 Years of Age: The Growing-Up Milk-Lite (GUMLi) Randomized Controlled Trial.

Background: Iron deficiency (ID) and vitamin D deficiency (VDD) are significant pediatric health issues in New Zealand and Australia and remain prevalent micronutrient deficiencies in young children globally. Objective: We aimed to investigate the effect of a micronutrient-fortified, reduced-energy growing-up milk (GUMLi) compared with cow milk (CM) consumed for 1 y on dietary iron and vitamin D intakes and the status of New Zealand and Australian children at 2 y of age. Methods: The GUMLi Trial was a multicenter, double-blind, randomized controlled trial in 160 healthy 1-y-old New Zealand and Australian children conducted in 2015-2017. Participants were randomly assigned 1:1 to receive GUMLi (1.7 mg Fe/100 mL; 1.3 µg cholecalciferol/100 mL) or CM (0.02 mg Fe/100 mL; 0.06 µg cholecalciferol/100 mL) for 12 mo. Secondary outcomes, reported here, included change in dietary iron and vitamin D intakes, iron status, and 25-hydroxyvitamin D [25(OH)D] concentrations from blood samples at age 2 y. All regression models were adjusted for baseline outcome and study center. Results: GUMLi was a large contributor to dietary intakes of iron and vitamin D after 12 mo when compared with intakes from food and CM. The adjusted mean difference between groups for serum ferritin concentrations was 17.8 µg/L (95% CI: 13.6, 22.0 µg/L; P < 0.0001), and for 25(OH)D it was 16.6 nmol/L (95% CI: 9.9, 23.3 nmol/L; P < 0.0001). After 12 mo, ID was present in 16 (24%) participants in the CM group and 5 (7%) participants in the GUMLi group (P = 0.009), and the prevalence of VDD in the CM group increased to 14% (n = 10) and decreased to 3% (n = 2) (P = 0.03) in the GUMLi group. Conclusion: In comparison with CM, GUMLi significantly improved dietary iron and vitamin D intakes and the iron and vitamin D status of healthy children at 2 y of age. This trial was registered with the Australian New Zealand Clinical Trials Registry (www.anzctr.org.au) as ACTRN12614000918628.

Determinants of folic acid supplement use outside national recommendations for pregnant women: results from the Growing Up in New Zealand cohort study.

OBJECTIVE: To evaluate the sociodemographic and lifestyle factors associated with insufficient and excessive use of folic acid supplements (FAS) among pregnant women. DESIGN: A pregnancy cohort to which multinomial logistic regression models were applied to identify factors associated with duration and dose of FAS use. SETTING: The Growing Up in New Zealand child study, which enrolled pregnant women whose children were born in 2009-2010. SUBJECTS: Pregnant women (n 6822) enrolled into a nationally generalizable cohort. RESULTS: Ninety-two per cent of pregnant women were not taking FAS according to the national recommendation (4 weeks before until 12 weeks after conception), with 69 % taking insufficient FAS and 57 % extending FAS use past 13 weeks' gestation. The factors associated with extended use differed from those associated with insufficient use. Consistent with published literature, the relative risks of insufficient use were increased for younger women, those with less education, of non-European ethnicities, unemployed, who smoked cigarettes, whose pregnancy was unplanned or who had older children, or were living in more deprived households. In contrast, the relative risks of extended use were increased for women of higher socio-economic status or for whom this was their first pregnancy and decreased for women of Pacific v. European ethnicity. CONCLUSIONS: In New Zealand, current use of FAS during pregnancy potentially exposes pregnant women and their unborn children to too little or too much folic acid. Further policy development is necessary to reduce current socio-economic inequities in the use of FAS.

Maternal health in pregnancy and associations with adverse birth outcomes: Evidence from Growing Up in New Zealand.

OBJECTIVE: To examine prospectively multiple indicators of pregnancy health and associations with adverse birth outcomes within a large, diverse sample of contemporary women. DESIGN: A cohort of pregnant women who gave birth during 2009-10. POPULATION: We enrolled a sample of 6822 pregnant New Zealand (NZ) women: 11% of all births in NZ during the recruitment period. METHODS: We analysed a number of maternal health indicators and behaviours during pregnancy in relation to birth outcomes using multivariable logistic regression. Associations were described using adjusted odds ratios and 95% confidence intervals. MAIN OUTCOME MEASURES: Three birth outcomes, low birth weight (LBW), pre-term birth (PTB) and delivery type, were measured via linkage with maternity hospital perinatal databases. Small for gestational age (SGA) was then defined as below the 10th percentile by week of gestation. RESULTS: Modelling of birth outcomes after adjusting for confounders indicated patterns of increased risk of LBW and PTB for women who smoke, have elevated pre-pregnancy body mass index (BMI), or with insufficient pregnancy weight gain. SGA was associated with maternal smoking, alcohol use, insufficient weight gain and nausea and vomiting during pregnancy. Risk of caesarean section was associated with having a diagnosed illness before pregnancy, elevated BMI, greater pregnancy weight gain and less pregnancy exercise. Number of risk factor variables were then used to model birth outcomes. Women with multiple risk factors were at increased risk compared with those who had no risk factors. CONCLUSIONS: Women with multiple health risks are at particular risk of adverse birth outcomes.

Ethnic disparities in infectious disease hospitalisations in the first year of life in New Zealand.

AIM: Infectious disease (ID) hospitalisation rates are increasing in New Zealand (NZ), especially in pre-school children, and Maori and Pacific people. We aimed to identify risk factors for ID hospitalisation in infancy within a birth cohort of NZ children, and to identify differences in risk factors between ethnic groups. METHODS: We investigated an established cohort of 6846 NZ children, born in 2009-2010, with linkage to a national data set of hospitalisations. We used multivariable logistic regression to obtain odds ratios (OR) for factors associated with ID hospitalisation in the first year of life, firstly for all children, and then separately for Maori or Pacific children. RESULTS: In the whole cohort, factors associated with ID hospitalisation were Maori (OR: 1.49, 95% CI: 1.17-1.89) or Pacific (2.51; 2.00-3.15) versus European maternal ethnicity, male gender (1.32; 1.13-1.55), low birthweight (1.94, 1.39-2.66), exclusive breastfeeding for <4 months (1.22, 1.04-1.43), maternal experience of health-care racism (1.60, 1.19-2.12), household deprivation (most vs. least deprived quintile of households (1.50, 1.12-2.02)), day-care attendance (1.43, 1.12-1.81) and maternal smoking (1.55, 1.26-1.91). Factors associated with ID hospitalisation for Maori infants were high household deprivation (2.16, 1.06-5.02) and maternal smoking (1.48, 1.02-2.14); and for Pacific infants were delayed immunisation (1.72, 1.23-2.38), maternal experience of health-care racism (2.20, 1.29-3.70) and maternal smoking (1.59, 1.10-2.29). CONCLUSIONS: Maori and Pacific children in NZ experience a high burden of ID hospitalisation. Some risk factors, for example maternal smoking, are shared, while others are ethnic-specific. Interventions aimed at preventing ID hospitalisations should address both shared and ethnic-specific factors.

Internal living environment and respiratory disease in children: findings from the Growing Up in New Zealand longitudinal child cohort study.

BACKGROUND: The incidence of early childhood acute respiratory infections (ARIs) has been associated with aspects of the indoor environment. In recent years, public awareness about some of these environmental issues has increased, including new laws and subsequent changes in occupant behaviours. This New Zealand study investigated current exposures to specific risk factors in the home during the first five years of life and provided updated evidence on the links between the home environment and childhood ARI hospitalisation. METHODS: Pregnant women (n = 6822) were recruited in 2009 and 2010, and their 6853 children created a child cohort that was representative of New Zealand births from 2007-10. Longitudinal data were collected through face-to-face interviews and linkage to routinely collected national datasets. Incidence rates with Poisson distribution confidence intervals were computed and Cox regression modelling for repeated events was performed. RESULTS: Living in a rented dwelling (48%), household crowding (22%) or dampness (20%); and, in the child's room, heavy condensation (20%) or mould or mildew on walls or ceilings (13%) were prevalent. In 14% of the households, the mother smoked cigarettes and in 30%, other household members smoked. Electric heaters were commonly used, followed by wood, flued gas and unflued portable gas heaters. The incidence of ARI hospitalisation before age five years was 33/1000 person-years. The risk of ARI hospitalisation was higher for children living in households where there was a gas heater in the child's bedroom: hazard ratio for flued gas heater 1.69 (95% CI: 1.21-2.36); and for unflued gas heater 1.68 (95% CI: 1.12-2.53); and where a gas heater was the sole type of household heating (hazard ratio: 1.64 (95% CI: 1.29-2.09)). The risk was reduced in households that used electric heaters (Hazard ratio: 0.74 (95% CI: 0.61-0.89)) or wood burners (hazard ratio: 0.79 (95% CI: 0.66-0.93)) as a form of household heating. The associations with other risk factors were not significant. CONCLUSIONS: The risk of early childhood ARI hospitalisation is increased by gas heater usage, specifically in the child's bedroom. Use of non-gas forms of heating may reduce the risk of early childhood ARI hospitalisation.

Dietary Intake and Eating Behaviours of Obese New Zealand Children and Adolescents Enrolled in a Community-Based Intervention Programme.

OBJECTIVES: The aim of this study was to describe dietary intake and eating behaviours of obese children and adolescents, and also to determine how these differ in Indigenous versus non-Indigenous children at enrolment in an obesity programme. METHODS: Baseline dietary intake and eating behaviour records were assessed from those enrolled in a clinical unblinded randomised controlled trial of a multi-disciplinary intervention. The setting was a community-based obesity programme in Taranaki, New Zealand. Children or adolescents who were enrolled from January 2012 to August 2014, with a BMI ≥98th percentile or >91st centile with weight-related comorbidities were eligible. RESULTS: 239 participants (45% Maori, 45% NZ Europeans, 10% other ethnicities), aged 5-17 years were assessed. Two-thirds of participants experienced hyperphagia and half were not satiated after a meal. Comfort eating was reported by 62% of participants, and daily energy intake was above the recommended guidelines for 54%. Fruit and vegetable intake was suboptimal compared with the recommended 5 servings per day (mean 3.5 [SD = 1.9] servings per day), and the mean weekly breakfasts were less than the national average (5.9 vs 6.5; p<0.0001). Median sweet drink intake amongst Maori was twice that of NZ Europeans (250 vs 125 ml per day; p = 0.0002). CONCLUSIONS: There was a concerning prevalence of abnormal eating behaviours and significant differences in dietary intake between obese participants and their national counterparts. Ethnic differences between Indigenous and non-Indigenous participants were also present, especially in relation to sweet drink consumption. Eating behaviours, especially sweet drink consumption and fruit/vegetable intake need to be addressed.

Dietary Patterns in Pregnancy in New Zealand-Influence of Maternal Socio-Demographic, Health and Lifestyle Factors.

Exploration of dietary pattern associations within a multi-ethnic society context has been limited. We aimed to describe dietary patterns of 5664 pregnant women from the Growing Up in New Zealand study, and investigate associations between these patterns and maternal socio-demographic, place of birth, health and lifestyle factors. Participants completed a food frequency questionnaire prior to the birth of their child. Principal components analysis was used to extract dietary patterns and multivariable analyses used to determine associations. Four dietary components were extracted. Higher scores on, 'Junk' and 'Traditional/White bread', were associated with decreasing age, lower educational levels, being of Pacific or Maori ethnicity and smoking. Higher scores on, 'Health conscious' and 'Fusion/Protein', were associated with increasing age, better self-rated health, lower pre-pregnancy body mass index (BMI) and not smoking. Higher scores on 'Junk' and 'Health conscious' were associated with being born in New Zealand (NZ), whereas higher scores on 'Fusion/Protein' was associated with being born outside NZ and being of non-European ethnicity, particularly Asian. High scores on the 'Health conscious' dietary pattern showed the highest odds of adherence to the pregnancy dietary guidelines. In this cohort of pregnant women different dietary patterns were associated with migration, ethnicity, socio-demographic characteristics, health behaviors and adherence to dietary guidelines.

Maternal and perinatal predictors of newborn iron status.

AIM: To describe iron status at birth in a population sample of children. METHOD: Cord blood samples were obtained at birth from 131 infants enrolled in the cohort study Growing Up in New Zealand. Cord blood serum ferritin (SF) and haemoglobin (Hb) concentrations were measured and associations of SF and Hb with maternal and birth characteristics were determined. RESULTS: Demographics were comparable to the larger cohort, except for having a higher pre-pregnancy body mass index (26.9 vs. 25.4 kg/m2, P=0.005), lower frequency of cigarette smoking during pregnancy (2% vs. 11%, P=0.0004), and smaller proportion with birth-weight <2500 g (0% vs. 5%, P=0.03). Median (interquartile range) SF was 135 (88-180) mcg/L and mean (plus or minus SD) Hb was 160 plus or minus 17 g/L. Eight newborns (7%) had cord SF levels indicative of iron deficiency (SF <35 mcg/L), two newborns were anaemic (Hb <130 g/L) and none had iron deficiency anaemia. Median SF was lower in newborns whose mothers consumed greater than or equal to 3 servings of milk/day during the pregnancy (131 vs. 151 mcg/L, P=0.04). No other associations with SF or Hb were observed. CONCLUSION: Iron deficiency is present in 7% of newborns in New Zealand. Newborns whose mothers consumed more milk during pregnancy had a lower median SF concentration.

Could vitamin d have a potential anti-inflammatory and anti-infective role in bronchiectasis?

Bronchiectasis is a chronic infective and inflammatory respiratory disease that causes significant morbidity and mortality. Patients with non-cystic-fibrosis bronchiectasis are frequently vitamin D deficient, and vitamin D levels correlate with disease severity. Infection-specific actions of vitamin D include the enhancement of innate immunity and the moderation of inflammation caused by the adaptive immune response. Potentially, vitamin D could influence the processes that lead to bronchiectasis and the frequency and severity of acute exacerbations. Randomized trials of vitamin D supplementation have shown effects that are likely to be protective against the development of bronchiectasis. Several issues need to be clarified before the development of clinical trials to investigate the role of vitamin D in bronchiectasis. These include an optimal vitamin D supplementation dose and appropriate and sensitive outcome measures that include assessment of exacerbation frequency and severity, lung function, and health-related quality of life.

Risk factors for community-acquired pneumonia in pre-school-aged children.

AIM: To identify risk factors for children developing and being hospitalised with community-acquired pneumonia. METHODS: Children <5 years old residing in urban Auckland, New Zealand were enrolled from 2002 to 2004. To assess the risk of developing pneumonia, children hospitalised with pneumonia (n= 289) plus children with pneumonia discharged from the Emergency Department (n= 139) were compared with a random community sample of children without pneumonia (n= 351). To assess risk of hospitalisation, children hospitalised with pneumonia were compared with the children discharged from the Emergency Department. Adjusted odds ratio (OR) with 95% confidence intervals (CIs) were used to estimate the risk of pneumonia and hospitalisation with pneumonia. RESULTS: After adjustment for season, age and ethnicity there was an increased risk of pneumonia associated with lower weight for height (OR 1.28, 95% CI 1.10-1.51), spending less time outside (1.96, 1.11-3.47), previous chest infections (2.31, 1.55-3.43) and mould in the child's bedroom (1.93, 1.24-3.02). There was an increased risk of pneumonia hospitalisation associated with maternal history of pneumonia (4.03, 1.25-16.18), living in a more crowded household (2.87, 1.33-6.41) and one with cigarette smokers (1.99, 1.05-3.81), and mould in the child's bedroom (2.39, 1.25-4.72). CONCLUSIONS: Lower quality living environments increase the risk of pneumonia and hospitalisation with pneumonia in New Zealand. Poorer nutritional status may also increase the risk of pneumonia. Improving housing quality, decreased cigarette smoke exposure and early childhood nutrition may reduce pneumonia disease burden in New Zealand.

Helicobacter pylori infection and iron deficiency in teenage females in New Zealand.

BACKGROUND: Iron deficiency is an important problem in New Zealand children and young adults. Iron deficiency and Helicobacter pylori (H. pylori) infection are each more common in Maori and Pacific Island ethnic groups. AIMS: This study seeks to determine if H. pylori infection is associated with iron deficiency. METHODS: 792 female students from 7 Auckland high schools (median age 16 years) had H. pylori serology and tests for iron deficiency assessed by a combination of serum ferritin, iron saturation and mean cell volume. RESULTS: The prevalence of positive H. pylori serology was highest for Pacific Island students (49.0%; CI 38.0-60.0), intermediate for Maori (26.7%; CI 16.9-36.4) and Asian (24.7%; CI 12.6-36.7) and lowest for European (13.7%; 6.0-21.4) p<0.0001. Students with positive H. pylori serology had lower mean levels of iron saturation (p=0.013), but not of ferritin (p=0.068), haemoglobin (p=0.08) or mean cell volume (p=0.16), compared to those with negative serology. Positive H. pylori serology was associated with increased risk of iron deficiency (RR 1.20; CI 1.08-1.34), but not anaemia (RR 1.01; CI 0.87-1.18), after adjusting for age, ethnicity and school SES decile. CONCLUSIONS: This study indicates that H. pylori infection is associated with iron deficiency in adolescent females. There are significant differences in H. pylori serology amongst different ethnic groups in New Zealand.

Ethnic variance in iron status: is it related to dietary intake?

OBJECTIVE: In New Zealand (NZ), Fe deficiency (ID) is present in 14% of children aged <2 years. Prevalence varies with ethnicity (NZ European 7%, Pacific 17%, Maori 20%). We describe dietary Fe intake, how this varies with ethnicity and whether intake predicts Fe status. DESIGN: A random sample of children aged 6-23 months. Usual Fe intake and dietary sources were estimated from 2 d weighed food records. Associations were determined between adequacy of Fe intake, as measured by the Estimated Average Requirement (EAR), and ID. SUBJECTS: Sampling was stratified by ethnicity. Dietary and blood analysis data were available for 247 children. RESULTS: The median daily Fe intake was 8.3 mg (age 6-11 months) and 6.3 mg (age 12-23 months). Breast milk and milk formulas (median 58%; age 6-11 months), and cereals (41%) and fruit and vegetables (17%; age 12-23 months), were the predominant dietary sources of Fe. Fe intake was below the EAR for 25% of the children. Not meeting the EAR increased the risk of ID for children aged 6-11 months (relative risk = 18.45, 95% CI 3.24, 100.00) and 12-23 months (relative risk = 4.95, 95% CI 1.59, 15.41). In comparison with NZ European, Pacific children had a greater daily Fe intake (P = 0.04) and obtained a larger proportion of Fe from meat and meat dishes (P = 0.02). CONCLUSIONS: A significant proportion of young NZ children have inadequate dietary Fe intake. This inadequate intake increases the risk of ID. Ethnic differences in Fe intake do not explain the increased risk of ID for Pacific children.

Policy statement on iron deficiency in pre-school-aged children.

AIM: We aimed to develop policy in relation to three areas: (i) the diagnosis of iron deficiency; (ii) maternal-infant issues and the prevention of iron deficiency; and (iii) the treatment of iron deficiency. METHODS: Within each of these topic areas we completed a literature review and developed recommendations to help direct activities of the Royal Australasian College of Physicians, update paediatricians and guide clinical practice. RESULTS: Iron deficiency can be defined using cut-off values for laboratory measures of iron status or, if an intercurrent infection is not present, by demonstrating a response to a therapeutic trial of iron. The appropriate measures of iron status vary depending upon the presence of intercurrent infection. Full-term babies are born with iron stores sufficient to meet their needs to age 4-6 months but premature infants are not. After age 6 months infants are dependent upon dietary iron from complementary foods even with continued breastfeeding. Infants <33 weeks gestation or <1800 g birthweight should receive iron from 4 weeks of age. In most settings recommended treatment of iron deficiency is with oral ferrous sulphate as a single or twice daily dose of between 3 and 6 mg/kg/day. CONCLUSIONS: Iron deficiency is prevalent and an important determinant of child health. Precise and accurate diagnosis remains challenging. Iron supplementation is required for premature and low-birthweight infants. Oral iron salts remain the recommended treatment of choice in most instances.

Population prevalence and risk factors for iron deficiency in Auckland, New Zealand.

AIM: Previous prevalence estimates of iron deficiency (ID) in young New Zealand children are inaccurate because of sampling bias and imprecise definition of ID. The aim of this study was to estimate the prevalence of ID in children aged 6-23 months and the factors associated with ID. METHODS: An ethnically stratified sample identified from random residential address start points. Children resident in Auckland, New Zealand were enrolled from 1999 to 2002. Children with elevated C-reactive protein (>4 mg/L) were excluded. Iron status was determined in 324 (78%) of 416 enrolled children. Analyses adjusted for clustering and weighted for ethnic stratification. ID defined as abnormal values for two or more of serum ferritin (<10 microg/L), iron saturation (<10%) and mean cell volume (<73 fl). RESULTS: ID was present in 14% (95% confidence interval (CI) 9-17%). ID prevalence varied with ethnicity (Maori 20%, Pacific 17%, other 27%, New Zealand European 7%, P = 0.005), but not with social deprivation. In a multivariate analysis that adjusted for low birthweight, there was an increased risk of ID associated with a body mass index >or= 18.5 kg/m(2) (RR = 4.34, 95% CI 1.08-10.67), and with receiving no infant or follow on formula (RR = 3.60, 95% CI 1.56-6.49). CONCLUSIONS: ID is prevalent in young New Zealand children. Variance in ID prevalence with ethnicity but not social deprivation implies that cultural practices influence iron status. Young children with more rapid growth are at increased risk of ID as are those receiving milk other than that specifically modified for them.