Vitamin D Deficiency Associated With Increased Incidence of Gastrointestinal and Ear Infections in School-age Children

Post on January 15, 2013 by André Broussard, D.C.

Kathryn A. Thornton, DMD, MPH, Constanza Marín, RD, Mercedes Mora-Plazas, MSc, RD, Eduardo Villamor, MD, DrPH
Pediatr Infect Dis J. 2013;32(5):585-593.

Abstract

Background: Vitamin D deficiency (VDD) is highly prevalent among children worldwide. The effects of VDD include alterations of the immune response and increased risk of infection but little evidence exists in school-age children. We investigated the association of vitamin D status with morbidity in a prospective study of school-age children from Bogotá, Colombia.

Methods: We measured plasma 25-hydroxyvitamin D (25(OH)D) concentrations in a random sample of 475 children (mean ± standard deviation age: 8.9 ± 1.6 years) and followed them for an academic year. Caregivers were asked to record daily information on the incidence of morbidity episodes using pictorial diaries. Baseline vitamin D status was classified according to 25(OH)D concentrations as deficient (<50 nmol/L), insufficient (≥50 and <75 nmol/L) or sufficient (≥75 nmol/L). We used Poisson regression to estimate incidence rate ratios and 95% confidence intervals for days with diarrhea, vomiting, diarrhea with vomiting, cough with fever and earache or discharge with fever, comparing vitamin D-deficient with vitamin D-sufficient children. Estimates were adjusted for child’s age, sex and household socioeconomic status.

Results: The prevalence of VDD was 10%; an additional 47% of children were vitamin D-insufficient. VDD was associated with increased rates of diarrhea with vomiting (adjusted incidence rate ratio: 2.05; 95% confidence interval: 1.19, 3.53) and earache/discharge with fever (adjusted incidence rate ratio: 2.36; 95% confidence interval: 1.26, 4.44). VDD was not significantly related to cough with fever.

Conclusions: These results suggest that VDD is related to increased incidence of gastrointestinal and ear infections in school-age children. The effect of correcting VDD on reducing risk of these infections needs to be tested in supplementation trials.

Introduction

Inadequate vitamin D status is highly prevalent in children worldwide, even in equatorial regions where it had not been previously suspected. In Latin America, reported prevalence of vitamin D insufficiency and deficiency among children and adolescents ranges from 28% in Costa Rica[1] to 56% in Bogotá, Colombia[2] and 62% in São Paulo, Brazil.[3] Emerging evidence suggests that the consequences of vitamin D deficiency (VDD) extend beyond its well-known effects on bone metabolism and calcium homeostasis, and also include alterations of specific arms of immunity. The immunomodulatory properties of vitamin D may influence susceptibility to infection.[4] These effects are primarily mediated through the vitamin D receptor (VDR),[5] which is expressed in many cells of the immune system, including T and B lymphocytes, neutrophils, monocytes, macrophages and dendritic cells.[6–10]

Recent epidemiologic studies indicate that low plasma vitamin D concentrations are related to increased incidence of respiratory infections, including acute lower respiratory tract infections[11–14] and respiratory syncytial virus (RSV) disease[15] in infants and children less than 5 years of age. Furthermore, vitamin D supplementation in randomized controlled trials conducted among schoolchildren resulted in reduced incidence of influenza A infection[16] and acute respiratory infection.[17] In another trial among Afghan children less than 3 years of age, vitamin D supplementation decreased the risk of pneumonia;[18] nevertheless, a larger randomized controlled trial showed no effect among infants from the same setting.[19]

Infection is a significant cause of morbidity throughout childhood.[20] Among school-age children, respiratory and gastrointestinal infections account for increased school absenteeism and parental absenteeism from work,[21] as well as a sizeable proportion of physician visits.[22,23] However, relatively little is known about the effect of vitamin D on infection-related morbidity in children more than 5 years of age. We conducted a prospective study to investigate the association between VDD and morbidity among school-age children in Bogotá, Colombia. We hypothesized that vitamin D-deficient children are at increased risk of gastrointestinal and respiratory morbidity.

Materials and Methods

Study Population

This study was conducted in the context of the Bogotá School Children Cohort, an ongoing longitudinal investigation of health and nutrition in school-age children. Details on the cohort design[24] and vitamin D substudy[2] have been previously reported. Briefly, in February 2006, we recruited a randomly selected group of 3202 children aged 5–12 years who were enrolled in public primary schools in Bogotá. Because the public school system enrolls a majority of children from low-income and middle-income families in the city,[25] the sample is representative of children from these strata living in Bogotá. Information on sociodemographic characteristics and health habits of the children and their families was elicited from parents through a self-administered questionnaire at the time of enrollment (82% response). Anthropometric measurements and fasting blood samples were obtained from the children by trained research assistants who visited the schools in the following weeks. Using standardized techniques,[26] weight was measured to the nearest 0.1 kg with Tanita HS301 electronic scales (Tanita, Arlington Heights, IL), and height was measured to the nearest 1 mm with wall-mounted Seca 202 stadiometers (Seca, Hanover, MD).

During the academic year after enrollment into the cohort, parents or primary caregivers recorded daily information on the incidence of morbidity episodes using a pictorial diary that was distributed and returned weekly. The diaries have drawings that depict children with symptoms including vomiting, diarrhea, fever, stomach ache, cough and earache/discharge. Caregivers were asked to check each day the child demonstrated these symptoms. Recording in diaries does not require a high level of education, and previous studies suggest that they are adequate to capture incidence of morbidity in developing countries.[27–29]

The parents or primary caregivers of all children gave ritten informed consent prior to enrollment into the study. The study protocol was approved by the Ethics Committee of the National University of Colombia Medical School. The Institutional Review Board at the University of Michigan approved the use of data and samples from the study.

Laboratory Methods

Blood samples were collected by venipuncture in 2816 (88%) children at baseline, during the month of February 2006. This month is considered part of a slightly warmer time of year in Bogotá, but there is no substantial seasonal variation within the samples’ collection period. Packed in ice and protected from sunlight, the samples were transported to the National Institute of Health (Bogotá, Colombia) where plasma was separated from an ethylenediaminetetraacetic acid-coated aliquot and cryopreserved at -70°C until transportation to the United States. Quantification of plasma 25-hydroxyvitamin D (25(OH)D), a biomarker of vitamin D status,[30] was completed in 479 randomly selected samples at the Clinical and Epidemiologic Research Laboratory of Children’s Hospital Boston (Boston, MA). An enzyme immunoassay (Immunodiagnostics Systems Inc, Scottsdale, AZ) with a competitive binding technique was used to quantify concentrations of plasma 25(OH)D. The assay has a sensitivity of 5 nmol 25(OH)D/L, intraclass coefficient of variation (CV) of 5.3–6.7% and interclass CV of 4.6–8.7%. Samples were analyzed in duplicate.

Data Analysis

Vitamin D status, the main exposure of interest, was categorized according to plasma 25(OH)D concentrations as deficient (<50 nmol/L), insufficient (≥50 and <75 nmol/L) or sufficient (≥75 nmol/L).[31]The primary outcomes were rates of gastrointestinal and respiratory morbidity, including diarrhea, vomiting, diarrhea with vomiting, cough with fever and earache or ear discharge with fever. Report of these symptoms has been related to clinically diagnosed episodes of gastrointestinal and respiratory infections.[32–34] Rates were calculated as the number of days with each symptom or combination of symptoms divided by the number of days the child was under observation.

Four children without morbidity diaries were excluded from the analyses; thus, the final sample size was 475. To identify potential confounders of the association between vitamin D and morbidity, we first compared the distribution of baseline child and maternal characteristics according to vitamin D serostatus with the use of Cochran-Armitage and Wald tests for trend. Children’s height-for-age Z scores and body mass index-for-age Z scores were estimated according to the World Health Organization reference.[35] Maternal body mass index was calculated with measured height and weight in 26% of mothers and from self-reported data in the remaining. Household socioeconomic status corresponded to the government’s assigned stratum to each household for tax and planning purposes.

Next, we estimated incidence rate ratios (IRRs) and 95% confidence intervals (CIs) for morbidity among children with VDD and insufficiency compared with those who were vitamin D-sufficient using Poisson regression models with the log-link function. Adjusted estimates were obtained from multivariable models that included child’s age, sex and household socioeconomic status as covariates. We assessed whether the associations of vitamin D with morbidity differed between girls and boys by testing an interaction term between vitamin D status and sex with use of the likelihood ratio test. All analyses were conducted with Statistical Analysis System software (version 9.2; SAS Institute Inc, Cary, NC).

Results

The mean (± standard deviation) age of children at recruitment was 8.9 ± 1.6 years, and 52% of children were girls. The mean (± standard deviation) plasma concentration of 25(OH)D was 73.2 ± 19.8 nmol/L; 10.1% of children were vitamin D-deficient, whereas 46.7% of children were vitamin D-insufficient. Children contributed 62,642 days of observation with a median (interquartile range) 140 (91, 182) days per child; the distribution of total child-days did not vary significantly by vitamin D status. At baseline, vitamin D serostatus was inversely associated with female sex, age, body mass index-Z and single mother status (Table 1).

Children with VDD had higher rates of vomiting, diarrhea with vomiting and earache or ear discharge with fever than vitamin D-sufficient children (Table 2). Compared with children who were vitamin D-sufficient, those who were deficient had twice as many days with diarrhea and vomiting after adjustment for child’s age, sex and household socioeconomic status (P = 0.009). In addition, vitamin D-deficient children had 2.4 times as many days with earache or ear discharge with fever compared with vitamin D-sufficient children (P = 0.008). This association was particularly strong among boys (adjusted IRR: 5.74; 95% CI: 2.32, 14.18) compared with girls (adjusted IRR: 1.09; 95% CI: 0.46, 2.60; P test for interaction with sex = 0.001).

We noted that vitamin D-insufficient (25(OH)D ≥50 and <75 nmol/L) children had lower rates of earache or ear discharge with fever and cough with fever, compared with children with 25(OH)D ≥75 nmol/L. The relation with cough and fever was mainly apparent in girls; vitamin D-insufficient girls reported 66% fewer days of cough with fever than girls who were vitamin D-sufficient (adjusted IRR: 0.34; 95% CI: 0.26, 0.43), whereas no significant association was observed in boys (adjusted IRR: 1.10; 95% CI: 0.81, 1.50; P test for interaction with sex < 0.0001).Discussion

In this prospective study of school-age children, VDD was associated with increased rates of vomiting, diarrhea with vomiting and earache or ear discharge with fever. These associations persisted after adjustment for potential confounders, including age, sex and socioeconomic status.

The association of VDD with diarrhea and vomiting could represent an effect on incidence or severity of gastrointestinal infections. Diarrhea and vomiting are symptoms often present in children with acute viral and bacterial gastrointestinal infections.[36–40] Norovirus infection is a common cause of diarrhea with vomiting or vomiting alone in school-age children.[41–43] These symptoms are likely the result of the virus’s pathogenic effects on the intestinal epithelial barrier.[44] A protective effect of vitamin D in the course of norovirus infection could be related to VDR-mediated upregulation of tight junction proteins expressed in the intestinal epithelium.[45,46] Bacterial agents, such as Salmonella and Shigella, also cause diarrhea and vomiting in school-age children.[47,48] Animal and in vitro studies have demonstrated that VDR expression is associated with reduced Salmonella colonization and mucosal invasion.[49] Shigella can downregulate expression of antimicrobial peptides, a component of the innate immune system that serves as part of the first line of mucosal defense against invading pathogens.[50] On the contrary, vitamin D influences innate immunity through expression of the cathelicidin antimicrobial peptide gene as well as promotion of macrophage activity.[51,52] Thus, vitamin D-deficient children may be more susceptible to develop more severe symptoms or may be more likely to become infected with these microorganisms through different mechanisms that are likely pathogen-specific.

Few previous studies have reported on the potential effect of vitamin D on gastrointestinal infections in children (Table 3). Tanzanian children born to mothers with serum 25(OH)D <80 nmol/L during pregnancy had no increased risk of diarrhea over a median follow-up time of 58 months.[56] Vitamin D supplementation in a randomized controlled trial in school-age children did not reduce the incidence of gastroenteritis, a secondary outcome of the trial.[16] Consistent with our findings, a cross-sectional study of 458 Qatari children reported a significantly higher prevalence of gastroenteritis among those who were vitamin D-deficient.[65] However, in this cross-sectional study, vitamin D status was measured concurrently with disease diagnosis; thus, the potential for reverse causation in which infection may have affected 25(OH)D concentrations cannot be excluded. Immune cells are able to alter vitamin D metabolism in several diseases.[68]

We also found that VDD was associated with increased report of days with earache or ear discharge and fever, especially among boys. These symptoms are typical of otitis media, usually caused by bacteria including Haemophilus influenzae, Moraxella catarrhalis and Streptococcus pneumoniae.[69,70]Increased production of antimicrobial peptides that form part of the initial mucosal defense in the respiratory tract is one possible mechanism through which vitamin D might enhance resistance to infection by these pathogens.[71] Although an association of VDD with ear infection has not been documented before, previous investigations suggest a protective role of vitamin D against other respiratory tract infections. In infants and children, maternal or child 25(OH)D serum or plasma levels have been inversely associated with risk or severity of acute lower respiratory infection,[11–14,57,59]RSV[15] or tuberculosis.[67] In addition, a polymorphism of the VDR gene was associated with higher risk of severe RSV disease in case-control studies of hospitalized children with RSV infection in The Netherlands and South Africa.[72,73] By contrast, 1 case-control study of Yemeni children found an inverse relation between VDD and chronic suppurative otitis media.[62] This study may have been limited by reverse causation bias given that 25(OH)D levels were measured in children who had had ear discharge for at least 2 weeks before enrollment. Although VDD increased the risk of earache/discharge with fever in our cohort, vitamin D insufficiency was associated with a reduced incidence of these symptoms. Whether this might be due to heterogeneity in the etiology of ear disease deserves further investigation. Chronic suppurative otitis media involves a broader spectrum of bacterial pathogens than acute otitis media,[74] and the nonlinearity of the association of vitamin D status with ear symptoms in our study may represent a weaker or detrimental effect of vitamin D on chronic infection than on the acute forms of disease.

Although several previous studies have found increased risk of respiratory illness with VDD, we did not find an elevated rate of cough with fever among vitamin D-deficient school-age children. Most of the literature describing the effects of vitamin D on infection in children has been limited to age groups less than 5 years. It is possible that the effect of vitamin D on respiratory illness varies among children of different ages because the pathogens involved in the etiology of respiratory infection differ. For example, in a study of children hospitalized with lower respiratory tract infections, the proportion of infections due to viral agents was highest in infants, whereas the proportion of identifiable infections attributable to bacterial pathogens was greatest in children more than 5 years of age.[75] Cough and fever are nonspecific symptoms of respiratory infections, such that they cannot be used to differentiate among the potential etiologic agents of disease, including viruses, bacteria and atypical organisms.[76]We relied on self-reported symptoms of common childhood infections but it was not possible to establish clinical diagnoses or confirm an infectious etiology of the reported morbidities.

It is unclear why the association between vitamin D serostatus and rates of earache/discharge with fever and cough with fever varied by sex. Randomized trials show sex-differential effects of vitamin A supplementation administered with bacille Calmette-Guérin vaccine with respect to vaccine response, mortality and measles incidence.[77–80] While boys demonstrated a more prominent Th1 profile than girls, girls had a more robust Th2 profile. Data from in vitro and animal studies generally show that vitamin A enhances the Th2-type response to infection.[81] Vitamin D similarly dampens the Th1-type response in favor of a Th2-type response,[82] and this might help explain the differential effects of inadequate vitamin D status on morbidity in boys and girls.

One strength of our study is its longitudinal design, which largely precludes the possibility of reverse causation bias. In addition, prospective collection of information on the morbidity events prevents the occurrence of outcome misclassification bias due to differential recall. A possible limitation is the use of 1 measurement of 25(OH)D levels to ascertain exposure status at baseline. However, repeated measures of 25(OH)D concentrations over time indicate that within-subject correlation is high, suggesting that a single measurement could represent long-term exposure.[83]

In summary, VDD was associated with increased rates of ear and gastrointestinal morbidity in a cohort of school-age children. These results add to the growing body of evidence supporting a role for vitamin D in the susceptibility to infection-related illness in children. Randomized intervention trials are needed to ascertain whether vitamin D supplementation reduces the risk of otitis media and gastrointestinal morbidities experienced in children more than 5 years of age.

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