Background: The changes in serum 25-hydroxyvitamin D (25(OH)D) in adolescents from summer to winter and optimal serum vitamin D levels in the summer to ensure adequate vitamin D levels at the end of winter are currently unknown. This study was conducted to address this knowledge gap. Methods: The study was conducted as a cohort study. Sixty-eight participants aged 7-18 years and who had sufficient vitamin D levels at the end of the summer in 2011 were selected using stratified random sampling. Subsequently, the participants' vitamin D levels were measured at the end of the winter in 2012. A receiver operating characteristic (ROC) curve was used to determine optimal cutoff points for vitamin D at the end of the summer to predict sufficient vitamin D levels at the end of the winter. Results:The results indicated that 89.7% of all the participants had a decrease in vitamin D levels from summer to winter: 14.7% of them were vitamin D-deficient, 36.8% had insufficient vitamin D concentrations and only 48.5% where able to maintain sufficient vitamin D. The optimal cutoff point to provide assurance of sufficient serum vitamin D at the end of the winter was 40 ng/mL at the end of the summer. Sex, age and vitamin D levels at the end of the summer were significant predictors of non-sufficient vitamin D at the end of the winter.

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Purpose: One of the modifiable risk factors for esophageal cancer(EC) is hot beverages, but different studies have reported conflicting results. We aimed to identify the role of drinking habits in the development of EC in Iranian people. Methods: This hospital-based case-control study was carried out on 96 people with EC and 187 subjects as controls in North Khorasan province, Iran. Socio-demographic factors and drinking habits were collected by using validated questionnaires. The association between EC and drinking habits was estimated after adjusting the effects of confounding factors such as ethnicity, education level and family history of cancer in STATA software with 95% CI. Results: The average temperature of tea drinking in case groups were significantly higher compared to the control groups (56.9±5.9 vs 52.9±4.6ÕC, P=0.001). The tea temperature above 65° C and consumption of tea more than four times in one day, increased the risk of EC (OR: 6.1, 95% CI: 1.4-26.2, P=0.01 and OR: 10.3, 95% CI: 3.9-27.5, P<0.001, respectively). There was no significant association between cooking methods of foods and the risk of EC. Conclusion: This study showed an association between tea temperature and the volume of tea consumption with the risk of EC. Avoiding hot food and drink may help prevent ESCC. It is suggested to design the appropriate educational intervention about prevention of these risk factors.