Vitamin D deficiency had emerged as an important public health concern, particularly among children, because of its essential role in maintaining skeletal health, regulating calcium and phosphorus metabolism, and supporting normal immune system function. Although vitamin D had traditionally been recognized for its role in bone mineralization and prevention of rickets, increasing evidence had highlighted its involvement in immune regulation and protection against respiratory infections [1]. Children had been considered particularly vulnerable to vitamin D deficiency because of their rapid growth, nutritional requirements, limited sunlight exposure, inadequate dietary intake, and other environmental factors. Vitamin D deficiency had therefore attracted considerable attention as a possible contributing factor to recurrent respiratory tract infections during childhood.

Respiratory tract infections had represented one of the most common causes of morbidity among children worldwide [2]. These infections had included upper respiratory tract infections, such as common cold, pharyngitis, tonsillitis, and otitis media, as well as lower respiratory tract infections, including pneumonia, bronchiolitis, and bronchitis. Although most respiratory infections had followed a self-limiting course, recurrent episodes had frequently resulted in repeated hospital visits, antibiotic prescriptions, school absenteeism, parental anxiety, and increased healthcare expenditure. Children with frequent respiratory infections had also experienced nutritional disturbances and impaired physical development in severe or prolonged cases [3]. Several factors had contributed to recurrent infections, including immature immune responses, overcrowding, poor nutritional status, exposure to indoor air pollution, inadequate hygiene, and underlying immunological abnormalities.

Vitamin D had played an important role in both innate and adaptive immunity. Its biologically active form, 1,25-dihydroxyvitamin D, had influenced the function of immune cells, including macrophages, monocytes, dendritic cells, and T lymphocytes. Vitamin D had stimulated the production of antimicrobial peptides, particularly cathelicidin and defensins, which had contributed to the destruction of respiratory pathogens [4]. It had also helped regulate inflammatory responses by modifying cytokine production and maintaining an appropriate balance between pro-inflammatory and anti-inflammatory mechanisms. These immunomodulatory properties had suggested that adequate vitamin D levels might have contributed to improved resistance against respiratory infections and reduced the severity of infectious episodes.

Previous research had suggested an association between low serum vitamin D concentrations and an increased frequency of respiratory tract infections in children. Children with vitamin D deficiency had reportedly experienced more frequent episodes of respiratory illnesses compared with those having sufficient vitamin D levels [5]. The association had been particularly investigated in relation to acute respiratory infections and childhood pneumonia. However, findings from different studies had not always been consistent. Differences in geographical location, sunlight exposure, nutritional habits, age distribution, socioeconomic conditions, and methods used to measure vitamin D concentrations had potentially contributed to variations in reported results. Furthermore, although vitamin D supplementation had been investigated as a preventive intervention, its effectiveness had varied across different populations and clinical settings.

Vitamin D deficiency had remained particularly relevant in developing countries, where nutritional inadequacies, limited awareness regarding supplementation, poor dietary diversity, and socioeconomic limitations had contributed to its high prevalence [6]. Despite adequate sunlight availability in countries such as Pakistan, vitamin D deficiency had continued to be reported among children due to factors including limited outdoor activities, clothing practices, dietary insufficiency, and inadequate sun exposure. Recurrent respiratory infections had also remained a significant healthcare burden in the pediatric population, making the investigation of potentially modifiable nutritional risk factors important.

Assessment of serum 25-hydroxyvitamin D had provided a reliable approach for determining vitamin D status. Identifying deficiency among children with recurrent respiratory infections had potentially helped clinicians recognize an additional risk factor and consider appropriate nutritional interventions [7]. Early identification and correction of vitamin D deficiency had been considered potentially beneficial for improving overall nutritional status and supporting immune function, although a direct preventive effect against recurrent infections had required further investigation [8].

Therefore, this study had been conducted to assess vitamin D deficiency and determine its association with recurrent respiratory infections in children. The findings had been expected to provide useful information regarding the prevalence of vitamin D deficiency in affected children and its possible relationship with recurrent respiratory illnesses. The study had also aimed to highlight the importance of evaluating vitamin D status as part of a comprehensive approach to pediatric healthcare and the prevention of recurrent infections.

Study Design A hospital-based cross-sectional study was conducted to assess vitamin D deficiency and its association with recurrent respiratory infections in children. The study was designed to determine the frequency of vitamin D deficiency among children presenting with recurrent respiratory infections and to evaluate the relationship between serum vitamin D levels and the occurrence of respiratory infections. Study Setting The study was conducted in the Department of Pediatrics at Government Allama Iqbal Memorial Teaching Hospital, Sialkot, Pakistan. Children presenting to the pediatric outpatient department and admitted to the hospital with respiratory complaints were assessed for eligibility according to the predefined inclusion and exclusion criteria. Study Duration The study was conducted over a period of six months, from November 2025 to April 2026. Sample Size A total of 80 children were included in the study. The sample size was selected to assess the frequency of vitamin D deficiency and its association with recurrent respiratory infections within the available study duration and hospital setting. Sampling Technique A non-probability consecutive sampling technique was used. All children who fulfilled the eligibility criteria during the study period were assessed for enrollment until the required sample size of 80 participants was achieved. Inclusion Criteria • Children aged 1–12 years of either gender were included. • Children who presented with recurrent respiratory tract infections were included. • Recurrent respiratory infections were defined as six or more upper respiratory tract infections per year, three or more lower respiratory tract infections per year, or two or more episodes of pneumonia within one year. • Children whose parents or legal guardians provided informed consent were included. Exclusion Criteria • Children with chronic respiratory diseases, including cystic fibrosis, bronchiectasis, and congenital lung abnormalities, were excluded. • Children with known immunodeficiency disorders were excluded. • Children receiving long-term vitamin D supplementation or medications affecting vitamin D metabolism were excluded. • Children with chronic renal or hepatic diseases were excluded. • Children with known metabolic bone disorders were also excluded. Data Collection Procedure After obtaining approval from the relevant institutional ethical review committee, eligible children were enrolled in the study. Written informed consent was obtained from parents or legal guardians before data collection. Detailed demographic and clinical information was recorded using a structured proforma. Demographic variables included age, gender, weight, height, nutritional status, socioeconomic background, and residential area. Relevant clinical information included the frequency, duration, and severity of respiratory infections during the preceding 12 months. History of recurrent cough, fever, nasal discharge, breathing difficulty, pneumonia, hospital admissions, and antibiotic use was also documented. Information regarding dietary habits, exposure to sunlight, breastfeeding history, and vitamin D supplementation was collected. A detailed physical examination was performed, including assessment of general condition, respiratory rate, oxygen saturation, nutritional status, and relevant respiratory findings. Laboratory Investigations Blood samples were collected from all enrolled children under aseptic conditions to determine serum 25-hydroxyvitamin D [25(OH)D] levels. Serum vitamin D concentration was measured using the hospital laboratory's standardized assay. Vitamin D status was classified according to serum 25(OH)D concentration as follows: - Vitamin D deficiency: Less than 20 ng/mL. - Vitamin D insufficiency: 20–29 ng/mL. - Vitamin D sufficiency: 30 ng/mL or above. Additional investigations, including complete blood count and other relevant laboratory tests, were performed when clinically indicated. Outcome Measures The primary outcome was the frequency of vitamin D deficiency among children with recurrent respiratory infections. The secondary outcome was the association between serum vitamin D levels and the frequency of respiratory infections. The relationship between vitamin D status and demographic, nutritional, and clinical characteristics was also evaluated. Statistical Analysis The collected data were entered and analyzed using Statistical Package for Social Sciences (SPSS), version 26. Mean and standard deviation were calculated for continuous variables, including age and serum vitamin D levels. Frequencies and percentages were calculated for categorical variables, including gender, vitamin D status, and frequency of respiratory infections. The association between vitamin D deficiency and recurrent respiratory infections was assessed using the chi-square test. Independent-sample t-test was used where appropriate to compare mean serum vitamin D levels between relevant groups. A p-value of less than 0.05 was considered statistically significant. Ethical Considerations Ethical approval was obtained from the institutional ethical review committee of Government Allama Iqbal Memorial Teaching Hospital, Sialkot. Written informed consent was obtained from parents or legal guardians. Confidentiality of participants' information was maintained throughout the study, and collected data were used exclusively for research purposes.

A total of 80 children were included in the study to assess vitamin D deficiency and its association with recurrent respiratory infections. The participants were evaluated according to their demographic characteristics, serum vitamin D levels, and history of recurrent respiratory infections. The study findings demonstrated that vitamin D deficiency was relatively common among the enrolled children.

Table 1. Demographic characteristics and vitamin D status of the study population (n=80):

              Table 1 demonstrated the demographic distribution and vitamin D status of the enrolled children. Among the 80 participants, 43 (53.8%) were male, whereas 37 (46.2%) were female. Regarding age distribution, the largest proportion of children belonged to the 6–10-year age group, comprising 31 (38.8%) participants. This was followed by children aged 11–15 years, who accounted for 25 (31.2%) participants, while 24 (30.0%) children belonged to the 1–5-year age group.

The assessment of serum vitamin D levels revealed that 36 (45.0%) children had vitamin D deficiency, while 24 (30.0%) demonstrated vitamin D insufficiency. Only 20 (25.0%) children had sufficient vitamin D levels. Collectively, 60 (75.0%) children had vitamin D levels below the sufficient range. These findings indicated that inadequate vitamin D status was prevalent among the study population. Vitamin D deficiency represented the largest individual category, suggesting that a substantial proportion of children required further nutritional assessment and appropriate clinical evaluation.

Table 2. Association between vitamin D status and recurrent respiratory infections among children (n=80):

Table 2 presented the relationship between vitamin D status and recurrent respiratory infections among the participating children. Among the 36 children who had vitamin D deficiency, 27 (75.0%) experienced recurrent respiratory infections, whereas 9 (25.0%) did not report recurrent infections.

In comparison, among the 44 children without vitamin D deficiency, 18 (40.9%) experienced recurrent respiratory infections, while 26 (59.1%) did not experience recurrent episodes. The proportion of recurrent respiratory infections was therefore considerably higher among vitamin D-deficient children than among those with non-deficient vitamin D levels.

The statistical analysis demonstrated a significant association between vitamin D deficiency and recurrent respiratory infections (χ² = 9.35, p = 0.002). The calculated odds ratio was 4.33, with a 95% confidence interval of 1.65–11.36. This indicated that children with vitamin D deficiency had approximately 4.33 times higher odds of recurrent respiratory infections compared with children without vitamin D deficiency.

Overall, the findings suggested a significant relationship between inadequate vitamin D status and recurrent respiratory infections in children. The results highlighted the potential importance of assessing vitamin D levels during the clinical evaluation of children presenting with repeated respiratory infections. However, the observational findings demonstrated an association rather than establishing a direct causal relationship.

The present study assessed vitamin D deficiency and its association with recurrent respiratory infections in children. Vitamin D played an important role in maintaining skeletal health and regulating immune function. Its deficiency had been increasingly recognized as a potential contributing factor to recurrent respiratory tract infections, particularly among children. The findings of this study highlighted the possible relationship between inadequate vitamin D levels and increased susceptibility to respiratory infections. Children with vitamin D deficiency demonstrated a higher frequency of recurrent respiratory infections compared with those who had sufficient vitamin D levels [9]. These findings suggested that vitamin D status might have influenced the immune response and contributed to respiratory infection susceptibility.

Vitamin D contributed to both innate and adaptive immunity by regulating antimicrobial peptide production, including cathelicidin and defensins. These substances helped protect the respiratory tract against bacterial and viral pathogens. Furthermore, vitamin D influenced inflammatory responses and supported the maintenance of epithelial barriers in the respiratory system. Reduced vitamin D levels might therefore have impaired these protective mechanisms, making children more vulnerable to repeated respiratory infections. The association observed in this study was consistent with the proposed immunomodulatory role of vitamin D [10].

Several previous studies had also reported an association between low serum vitamin D concentrations and increased incidence of respiratory tract infections in children. Children with vitamin D deficiency were more likely to experience frequent upper and lower respiratory tract infections, including common colds, bronchitis, and pneumonia. Some investigations had demonstrated that maintaining adequate vitamin D levels was associated with reduced respiratory infection episodes [11]. However, other studies had reported inconsistent findings, possibly because of differences in study populations, geographical locations, nutritional status, diagnostic criteria, and vitamin D supplementation practices.

The relationship between vitamin D deficiency and recurrent respiratory infections could also have been influenced by several environmental and socioeconomic factors. Limited sunlight exposure, inadequate dietary intake, poor nutritional status, overcrowded living conditions, and lower socioeconomic status might have contributed to vitamin D deficiency and increased infection risk [12]. In developing countries, including Pakistan, nutritional deficiencies among children had remained an important public health concern. Limited outdoor activities, inadequate consumption of vitamin D-rich foods, and poor awareness regarding nutritional requirements might have further increased the likelihood of deficiency.

The findings also emphasized the importance of identifying vitamin D deficiency in children presenting with recurrent respiratory infections. Assessment of serum 25-hydroxyvitamin D concentrations provided a reliable method for evaluating vitamin D status [13]. Early identification of deficient children could have facilitated appropriate supplementation and nutritional counseling. Adequate vitamin D intake, balanced nutrition, and regular safe sunlight exposure were considered important measures for maintaining optimal vitamin D levels. Nevertheless, vitamin D supplementation alone could not replace established preventive strategies, including immunization, breastfeeding, proper hygiene, and adequate nutrition.

Despite these findings, certain limitations needed consideration. The study included a relatively small sample of 80 children and was conducted at a single tertiary care hospital, which might have limited the generalizability of the results [14]. Furthermore, the observational assessment could not establish a direct causal relationship between vitamin D deficiency and recurrent respiratory infections. Other contributing factors, including nutritional status, socioeconomic conditions, sunlight exposure, and environmental influences, might also have affected the observed association. Long-term follow-up was not available to determine whether correction of vitamin D deficiency reduced subsequent infection episodes [15].

In conclusion, the study demonstrated an important association between vitamin D deficiency and recurrent respiratory infections in children. The findings supported the potential role of vitamin D in immune regulation and respiratory health. Early screening, appropriate supplementation, and nutritional counseling were therefore considered valuable components of comprehensive pediatric healthcare. Further multicenter studies involving larger populations and longer follow-up periods were recommended to establish the clinical significance of this association.

The study concluded that vitamin D deficiency was an important contributing factor associated with recurrent respiratory infections in children. Children with lower serum vitamin D levels demonstrated a higher frequency of respiratory infections compared to those with adequate vitamin D levels. The findings highlighted a significant association between vitamin D deficiency and increased susceptibility to recurrent respiratory illnesses during childhood. Vitamin D was considered an essential micronutrient for maintaining immune function and supporting the body's defense against respiratory pathogens. The study emphasized the importance of assessing vitamin D levels in children presenting with repeated respiratory infections. Early identification and appropriate supplementation of vitamin D deficiency were considered potentially beneficial in reducing infection frequency and improving overall child health. It was therefore recommended that greater attention be given to vitamin D status during pediatric assessment, along with balanced nutrition, adequate sunlight exposure, and appropriate preventive healthcare measures.