Independent association between air pollutants and vitamin D deficiency in young children in Isfahan, Iran.

OBJECTIVES

To determine the association between air pollution and vitamin D status in young children living in a sunny region.

METHODS

This cross-sectional study of 100 children aged 4-10 years in Isfahan was conducted during 2011-2012. This industrial city has an arid climate and is the second most air-polluted city in Iran. Children were selected by random cluster sampling from various areas with different levels of air pollution. The air quality index (AQI) was recorded and demographic variables, dietary habits and levels of physical activity were determined by validated questionnaires. Serum concentrations of 25-hydroxyvitamin D [25(OH)D], calcium, phosphate, alkaline phosphatase and parathyroid hormone were measured. The P for trend for median (interquartile range) of variables was assessed across the AQI quartiles. The associations between AQI and biochemical values were assessed by multiple linear regression after adjustment for age, gender, BMI, diet and pattern of physical activity.

RESULTS

Ninety-seven children (46.4% boys) completed the study. The median (interquartile range, IQR) of serum 25(OH) D was 37.4 (22.5, 81.6) nmol/L. Median dietary vitamin D intake was 11.7 μg/day, i.e. 78% of the required daily amount. Vitamin D deficiency and insufficiency were detected in 37.9% and 46.3% of children, respectively. Median (IQR) exposure to ultraviolet B radiation in the AQI Quartile 4 area was significantly lower than in the Quartile 1 area [0.36 (0.35-0.38) watts per square metre (W/m(2)) vs 0.41 (0.39-0.44) W/m(2), respectively, P = 0.04]. Likewise, the corresponding figure for serum 25(OH)D was 35.2 (22.5-45.2) vs 52.7 (44.9-81.6) nmol/L, respectively, P = 0.04. AQI was inversely associated with serum 25(OH)D, which remained significant after adjustment for the above-mentioned confounding factors (β = 0.61, P = 0.01).

CONCLUSION

The independent inverse association of AQI with 25(OH)D explains the high prevalence of vitamin D deficiency in children in Isfahan. Dietary intake of vitamin D was not sufficiently low to explain the very low level of serum 25(OH)D. In regions with plenty of sunlight, air pollution should be considered to be a factor in the causation of hypovitaminosis D.