Analysis of association between the height and sun exposure among Chinese children and adolescents

Objective To determine the association between height and the time of sun exposure in children and adolescents in China.Methods The data about children and adolescents aged 7-18 years of 31 provincial capital cities and municipalities was extracted from 2014 Chinese National Surveys on Students' Constitution and Health and environmental data was also collected from historical data.The sun exposure time was divided into five categories,including less than 1 000 hours,1 000-1 499 hours,1 500-1 999 hours,2 000-2 499 hours,and more than 2 500 hours.Height Z-score was calculated according to different ages and genders,and the change rules of the height of Z-score of boys and girls was analyzed according to different levels of sun exposure.Pearson correlation analysis and multilevel statistical models were used to evaluate the relationship between the height and the time of sun exposure.Results The correlation between height and average time of sun exposure has increasing trend along with the age in both sexes.The mean of height of Z-score gradually increase with the rising of time of sun exposure in the sun exposure grade of 1-4 level.In the fifth grade,the mean of height Z-score was lower than the fourth grade.There was the same trends in boys and girls.The stunting rate of children and adolescents was low in the region of high grade of sun exposure.According to the results of multilevel statistical models analysis,there was a positive relationship between the height Z-score and the time of sun exposure,and the risk of stunting of children and adolescents declined obviously in 2-5 levels of sun exposure compared with the lowest grade of sun exposure.Conclusion There is a positive association between time of sun exposure and height in children and adolescents aged 7-18 years.The influence of time of sun exposure on the height of students is higher in the region of high grade of sun exposure where the risk of stunting is lower compared to the region of lowest sun exposure.