Arch Pediatr Infect Dis. 2017 July; 5(3):e57276. Published online 2017 July 15. doi: 10.5812/pedinfect.57276. Research Article Role of Vitamin D [25(OH) D] Deficiency in Development of Pneumonia in Children Houman Hashemian, 1,* and Abtin Heidarzadeh 2 1 Pediatric Growth Disorders Research Center, 17thShahrivar Hospital, Faculty of Medicine, Guilan University of Medical Sciences, Rasht, IR Iran 2 Department of Community Medicine, Faculty of Medicine, Guilan University of Medical Sciences, Rasht, IR Iran * Corresponding author: Houman Hashemian, 17th Shahrivar Training Hospital, Rasht, Guilan, IR Iran. E-mail: hashemian@gums.ac.ir Received 2016 September 30; Revised 2017 March 01; Accepted 2017 March 28. Abstract Background: Pneumonia is a leading cause of children’s morbidity and mortality worldwide. Some studies have reported that vitamin D deficiency is associated with an increased incidence of lower respiratory illness requiring hospitalization. Objectives: Due to the weather conditions of Guilan province, Iran, in this study, we aimed at determining the relationship between serum level of vitamin D and developing pneumonia in children who were hospitalized due to pneumonia. Methods: In this case-control study, children aged 3 months to 5 years admitted in 17 Shahrivar hospital of Rasht, Iran, with pneu- monia were compared with healthy children of the same age as the control group. Serum levels of vitamin D in both groups were measured by chemiluminescence method. Results: In this study, 40 children aged 3 months to 5 years with pneumonia (19 males and 21 females) and 40 healthy children of the same age (22 males and 18 females) were studied. The mean serum levels of vitamin D in the group with pneumonia and the control group was 26.16 ± 15.2 ng/mL and 30.45 ± 15.69 ng/mL, respectively. The difference between the 2 groups was not significant (t test, P value = 0.218). However, this difference was significant in the age group of 24 to 60 months (t test, P value = 0.015). Conclusions: In this study, a significant relationship was observed between children’s vitamin D serum levels and development of pneumonia, only at the age of 24 to 60 months, although high prevalence of vitamin D deficiency in healthy children (control group) must be considered. The difference in the serum vitamin D levels of children with pneumonia and healthy children in the age group of 24 to 60 months suggest the need for preventive measures of vitamin D deficiency after infancy period. Keywords: Child, Pneumonia, Vitamin D Deficiency 1. Background Pneumonia is an inflammation of the lung parenchyma, and it is a leading cause of children’s morbidity and mortality worldwide, and along with di- arrhea, is the most common cause of death in children in developing countries. Approximately 158 million cases of pneumonia occur worldwide, and 154 million are in developing countries. Pneumonia causes 29% of all deaths in children younger than 5 years worldwide (1). Most cases of pneumonia are caused by microorgan- isms, but some noninfectious causes including aspiration of food or gastric foreign bodies, hydrocarbons, and hyper- sensitivity reactions to drugs or radiation-induced pneu- monitis are also involved. Pneumonia and its causes are difficult to prove because lung tissue (biopsy) culture is an aggressive procedure and is rarely done. Streptococcus pneumoniae (pneumococcus) is the most common bacte- rial pathogen in children aged 3 months to 4 years, while Mycoplasma pneumoniae and Chlamydia pneumoniae are common pathogens in children older than 5 years. Viruses are the main causes of lower respiratory tract infections in children younger than 5 years (1). An insufficient vitamin D level in the umbilical cord is associated with an increased risk of respiratory infec- tion within the first 3 months of life and wheezing in early childhood (2). The prevalence of vitamin D deficiency is higher in patients with severe bronchiolitis (3). Also, insuf- ficient serum level of vitamin D increases the risk of aller- gic and atopic diseases (4). Studies over the past 20 years have shown the rela- tionship between serum levels of vitamin D and an in- creased incidence and severity of TB infection. Vitamin D metabolism leads to activation of macrophages and in- hibits intracellular growth of Mycobacterium tuberculosis (5). Banajeh has reported that in patients with severe pneu- monia, vitamin D deficiency is strongly related to neu- tropenia and hypoxia (oxygen saturation less than 88%) (6). In some studies, vitamin D deficiency was associated with an increased incidence of lower respiratory tract disease requiring hospitalization (severe pneumonia) (7). This is because vitamin D may play a role in activating the innate immune system. Innate immune system activates Katheli- Copyright © 2017, Archives of Pediatric Infectious Diseases. 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