Healthy changes in some cardiometabolic risk factors accompany the higher summertime serum 25-hydroxyvitamin D concentrations in Iranian children: National Food and Nutrition Surveillance

Abstract

AbstractObjectiveTo investigate seasonal variations of vitamin D status at different latitudes and if these changes are accompanied by corresponding variations in certain health parameters in children living in a broad latitudinal range in Iran.DesignLongitudinal study.SubjectsIn total, 530 apparently healthy children aged 5–18 years were randomly selected from six regions of Iran with a latitudinal gradient from 29°N to 37·5°N. All anthropometric and biochemical assessments were performed twice during a year (summer, winter). High BMI (Z-score >1), low HDL cholesterol (<40 mg/dl, males; <50 mg/dl, females) and high TAG (>150 mg/dl) were considered cardiometabolic risk factors.ResultsSerum 25-hydroxyvitamin D (25(OH)D) showed between-season variation, with significantly higher concentrations (mean (sd)) in summer v. winter (43 (29) v. 27 (18) nmol/l; P<0·001). Change of circulating 25(OH)D between summer and winter was negatively correlated with change of BMI (r=−0·16; P<0·001), TAG (r=−0·09; P=0·04) and total cholesterol (r=−0·10; P=0·02) and directly correlated with change of height-for-age Z-score (r=0·09; P=0·04). Multiple stepwise linear regression analysis (β; 95 % CI) showed that winter serum 25(OH)D (−0·3; −0·4, −0·2; P<0·001), gender (boys v. girls: 9·7; 5·2, 14·1; P<0·001) and latitude (>33°N v. <33°N: 4·5; 0·09, 9·0; P=0·04) were predictors of change of serum 25(OH)D between two seasons.ConclusionsSummertime improvement of vitamin D status was accompanied by certain improved cardiometabolic risk factors, notably serum TAG, total cholesterol and BMI, in children.