Predictors of vitamin D status and its association with parathyroid hormone in young New Zealand children.

BACKGROUND

Despite increased awareness of the adverse health effects of low vitamin D status, few studies have evaluated 25-hydroxyvitamin D [25(OH)D] status in young children.

OBJECTIVES

We aimed to assess vitamin D status on the basis of 25(OH)D and its relation with parathyroid hormone (PTH) and to identify possible predictors of 25(OH)D status in young children living in a country with minimal vitamin D fortification.

DESIGN

Serum 25(OH)D and PTH concentrations were measured in a cross-sectional sample of children aged 12-22 mo [n = 193 for 25(OH)D, n = 144 for PTH] living in Dunedin, New Zealand (latitude: 45 degrees S). Anthropometric, dietary, and sociodemographic data were collected.

RESULTS

The majority of children sampled in the summer (94%; 47 of 50) had 25(OH)D >50 nmol/L; however, nearly 80% of children sampled in the winter (43 of 55) had serum concentrations < or =50 nmol/L. In season-adjusted multivariate analysis, breastfeeding and higher levels of education were independently associated with lower 25(OH)D concentrations, whereas male sex and cigarette-smoke exposure were positively associated with 25(OH)D (all P < 0.05). Fractional polynomial regression was used to describe the nonlinear relation between serum PTH and 25(OH)D (P < 0.001). When 25(OH)D concentrations were >60-65 nmol/L, a plateau in PTH was evident.

CONCLUSIONS

Seasonal variation in 25(OH)D concentration implies that postsummer vitamin D stores were insufficient to maintain status >50 nmol/L year-round. Examination of the predictors of 25(OH)D in our model shows few modifiable risk factors, and thus effective dietary strategies may be required if future research determines that children with 25(OH)D concentrations <50 nmol/L are at significant health risk. This trial was registered at www.actr.org.au as ACTRN12605000487617.