Vitamin D status and hospitalisation for childhood acute lower respiratory tract infections in Nigeria Patience Ahmed1, I. B. Babaniyi1, K. K. Yusuf1, Caitlin Dodd2, Gretchen Langdon2, Mark Steinhoff2, Adekunle Dawodu2 1
Department of Paediatrics, National Hospital Abuja, Abuja, Nigeria, 2Global Health Center, Cincinnati Children’s Hospital Medical Center/University of Cincinnati, Ohio, USA
Background: Acute lower respiratory tract infection (ALRTI) is the leading cause of childhood deaths in most developing countries, including Nigeria. Vitamin D is associated with innate immunity and may play a role in the control of infections. Case–control studies, including a small study from Nigeria, show inconsistent results for the association between vitamin D status and risk of ALRTI. Aims: To examine the relationship between vitamin D status and hospitalization for ALRTI in Nigerian children. Methods: Fifty children aged 2–60 months hospitalised with ALRTI were studied prospectively. ALRTI was diagnosed on the basis of modified WHO criteria. Each patient was matched with controls for age and gender. The controls were enrolled either from children attending well-child clinics or general clinics without evidence of respiratory infection or admitted to the hospital for elective surgery. A structured questionnaire collected data on demography, health, diet, duration of exposure to sunlight and percentage of body surface exposed to sunlight (according to type of clothing) while outdoors, and potential risk factors for ALRTI. Serum 25-hydroxyvitamin D [25(OH)D] concentration was measured using a chemiluminescenceimmuno-assay. The differences between cases and controls in serum 25(OH)D concentrations, association between vitamin D status and ALRTI and risk factors for vitamin D deficiency were assessed. Results: Mean (SD) 25(OH)D concentrations in patients and controls were similar [61.5 (25.8) vs 63.1 (22.9) nmol/L,P50.95].25% of all 100 subjects studied had serum 25(OH)D,50 nmol/L. In a multiple conditional logistic regression model, only lower percentage of body surface area exposed to sunlight was associated with increased risk of ALRTI. The percentage of body surface area exposed to sunlight while outdoors (P50.028) and vitamin D supplement use (P50.009) were independent determinants of vitamin D deficiency in the overall study population. Conclusions: ALRTI was not associated with vitamin D status, but was associated with less exposure to sunlight. Exposure to sunlight and vitamin D supplementation contributed to vitamin D status in this population. Keywords: Vitamin D, Lower respiratory infection, Children
Introduction The active metabolite of vitamin D (1,25-dihydroxyvitamin D) has been shown in both animal and invitro studies to be involved in innate immune responses.1 Recent in vitro studies demonstrate that vitamin D metabolites up-regulate the synthesis of intercellular antimicrobial peptide (cathelicidin) which is capable of killing micro-organisms and viruses.2 Vitamin D deficiency is linked to paediatric infections3 and a few case–control studies have reported associations
Correspondence to: P A Ahmed, Department of Paediatrics, National Hospital Abuja, Central District, PMB 425, Abuja, Nigeria. Email: [email protected]
ß W. S. Maney & Son Ltd 2014 DOI 10.1179/2046905514Y.0000000148
between vitamin D status and acute lower respiratory tract infections (ALRTI).4–8 A study from Bangladesh demonstrated an association between vitamin D deficiency and increased risk of ALRTI in early childhood.4 Other studies from India5 and Turkey6 linked vitamin D deficiency with severe ALRTI requiring hospitalisation. A study from Canada7 found no association between vitamin D status and the risk of hospitalisation for ALRTI, while another Canadian study found an association between serum 25-hydroxyvitamin D [25(OH)D],50 nmol/L (categorised as deficient) or ,75 nmol/L, (categorised as insufficient) and increased risk of severe pneumonia requiring intensive care.8 Together, these studies point
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to a possible contribution of vitamin D deficiency as a risk factor for ALRTI and support the theory that vitamin D supplementation could be a part of strategies to prevent childhood pneumonia. Acute lower respiratory tract infection, primarily pneumonia and bronchiolitis,9 is the leading cause of childhood deaths in most developing countries, including Nigeria.10 Although calcium deficiency has been suggested as an important cause of rickets in Nigerian children, vitamin D deficiency is the prevalent cause worldwide and also exists among Nigerian children with rickets.11,12 A study of children with rickets found an association with low calcium intake. However, 37% of the rachitic children had low vitamin D levels (serum 25(OH)D,30 nmol/L).12 Two studies from the Indian Sub-continent reported an increased risk of ARTI with low vitamin levels.4,5 Only one study with a small sample size has investigated the association between vitamin D status and ALRTI in Nigeria.13 The study compared 24 children hospitalized with pneumonia with ten controls and there was no significant difference in mean serum 25(OH)D concentrations between cases and controls. However, the authors reported that the two deaths and three cases of pneumonia complicated by empyema were associated with vitamin D insufficiency. The objective of this study was to examine the relationship between vitamin D status and the risk of hospitalisation for ALRTI.
At recruitment, each parent completed a structured questionnaire to collect data regarding parental education, religion, type of housing, exposure to smoke, immunisation, breastfeeding history, vitamin D supplementation, type of outdoor clothing and duration of exposure to sunlight in the week before interview or admission to hospital. Parents were asked about clothing covering the head, neck, face, arms, hands and legs while the child was outdoors. The total percentage of body surface area (BSA) exposed to sunlight was calculated using a formula for estimating BSA in children.15 The duration of skin exposure to sunlight and percentage BSA exposed to sunlight have been shown to correlate with vitamin D status in adults and children.16–18 Vitamin D supplement doses were calculated from the type and volume of vitamin syrup given to the infant. Weight and height were measured and each parameter was plotted on the WHO growth chart for children aged 0–5 years used by the institution, and a percentile recorded.19
Laboratory investigations On enrollment, 5 ml of venous blood was collected from each patient and control, and serum for measuring 25(OH)D concentrations was frozen at 220uC and shipped to Cincinnati Children’s Hospital, USA. The serum 25(OH)D concentration was determined using the DiaSorinLiaison 25(OH)D assay, according to manufacturer’s instructions. The intra- and inter-assay co-efficients of variation are ,8.5% and ,9.5%, respectively. Serum 25(OH)D concentration ,50 nmol/L, which is below the recommended target level for children, was categorized as vitamin D deficiency.20
Subjects and Methods This was a prospective study of 50 children aged 2– 60 months with ALRTI, recruited between November 2011 and September 2012 from the National Hospital, Abuja. There was a control for each case, matched for age and gender from the same location. Controls were enrolled either from children attending well-child clinics or general clinics without evidence of respiratory infections or admitted to the hospital for elective surgery. Controls were age-matched with cases to within 1 or 2 months. The admitting physicians diagnosed ALRTI on the basis of the modified WHO criteria which include a history of fever, cough, rapid breathing, lower chest-wall indrawing14 and/or abnormal auscultatory findings (crackles/crepitations or rhonchi, bronchial breath sounds), and radiological evidence of abnormal pulmonary parenchymal disease reported by a consultant radiologist. To exclude possible asthma, infants with bronchiolitis were those presenting with symptoms for the first time. Informed written or oral consent was obtained from the parents, and the study was approved by the National Hospital Abuja Ethics Committee.
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Sample size On the basis of the vitamin D status of Nigerian children with and without rickets12 and the reported higher rates of ALRTI in children with rickets,21 we extrapolated that children admitted with ALRTI would have a mean (SD) 25(OH)D of 34.8 (25.5) nmol/L, and that those without ALRTI would have a mean (SD) 25(OH)D of 51.3 (15.5) nmol/L. In order to detect this difference in means with a significance level of 0.05 and power of 90%, it was calculated that 36 children per group would be required. Allowing for a 30% rate of unexpected withdrawal or exclusion, 50 study subjects and 50 controls were enrolled.
Data analysis Summary descriptive socio-demographic, dietary and health statistics and vitamin D status of both groups were generated and all the variables were compared across cases and controls using a t-test if normally distributed. Continuous variables not normally distributed were compared across groups
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using a non-parametric test. Categorical variables were compared using x2 tests of association. The odds ratios for the association between ALRTI, serum 25(OH)D concentrations and other variables found to be significantly different between cases and controls were assessed using multiple conditional logistic regression. In a secondary analysis, the risk factors for vitamin D deficiency in the overall population of study children were investigated.
Results One hundred children aged between 2 and 60 months were recruited. Fifty children were admitted and treated for ALRTI (46 cases of pneumonia and four of bronchiolitis). Fifty children served as controls, as follows: 28 attending well-child clinics, 14 attending outpatient clinics with no history of respiratory disease, 7 with malarial fever, and one admitted for elective surgery. Mean (SD) age was similar between cases [12.9 (9.8) months] and controls [13.1 (10.5) months, P50.94]. Of the 100 infants enrolled, 56 were ,12 months, 28 were 12–24 months, 11 were 24–36 months, 4 were 36– 48 months and 2 were .48 months. Weight [8.4 (2.5) vs 9.1 (2.8) kg], months of exclusive breastfeeding [2.9 (2.6) vs 3.4 (2.3)], maternal post-secondary educational (62% vs 72%), western housing (94% vs 100%), hours of sunlight exposure per week [7.1 (9.1) vs 9.3 (13.4)], Islamic family religion (25% vs 34%), and use of vitamin D supplementation (20% vs 34%) were similar between cases and controls, respectively. Of the 27 infants who received vitamin D supplementation, 20 received 400 IU/day and 7 received 200 IU/day. Paternal post-secondary education (64% vs 80%), child’s mean (SD) weight for age [20.93 (1.39) vs 20.33 (1.43), P50.04] and weight for height [21.50 (2.15) vs 20.36 (2.24), P50.03] (Z-scores), and percentage BSA exposed to sunlight while outdoors [35% (16.0) vs 42% (13.0), P50.03] were significantly lower, respectively, in the cases than in the controls. Mean (SD) serum 25(OH)D concentrations were similar between cases and controls [61.5 (25.8) vs 63.1 (22.9) nmol/L, P50.95]. The difference in prevalence of vitamin D deficiency (serum 25(OH)D ,50 nmol/L) among cases (30%) and controls (20%) was not significant. The mean (SD) serum 25(OH)D concentration in samples (64) collected during the rainy season (April–October) and the dry season (36)
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(November–March) [64.4 (23.2) vs 58.5 (26.4)] were not significantly different. In multiple conditional logistic regression, the only variable that significantly influenced the odds of ALRTI was the percentage of BSA exposed to sunlight. A 10% decrease in body surface area exposed to sunlight was associated with approximately 1.8 increased odds of ALRTI (OR 1.79, 95% CI 1.02–3.16). Two of the cases died and two additional subjects with ALRTI had severe pneumonia with pleural empyema requiring chest tube drainage. The mean serum 25(OH)D concentration in these four severe cases was not significantly different than in other patients with ALRTI [65.9 (28.3)vs 63.1 (22.9)].
Predictors of vitamin D nutrition Although there were no significant differences in vitamin D status between cases and controls, 25 (25%) of all the children recruited had serum 25(OH)D levels ,50 nmol/L.20 Secondary analysis assessed the risk factors for vitamin D deficiency in the overall study population. Univariate analysis found that younger patient age [8.5 (7.2) vs 14.5 (10.6) months, P50.004], weekly hours of sunlight exposure [5.1 (10.0) vs 9.3 (11.8), P50.026] and vitamin D supplementation (5% vs 25%, P50.018] were associated with serum 25(OH)Dlevels ,50 nmol/L. The following variables were included in regression analyses: vitamin D supplementation, hours of exposure to sunlight, percentage BSA exposed outdoors, age, family religion, maternal education, paternal education and months of exclusive breastfeeding. Only percentage BSA exposed to sunlight while outdoors (P50.028) and vitamin D supplementation (P50.009) were independent predictors of serum 25(OH)D concentrations (Table 1). For each 10% increase in BSA exposed to sunlight, serum 25(OH)D concentrations increased by 3.5 nmol/L. Children who received vitamin D supplementation had serum 25(OH)D concentration almost 14 nmol/L higher than those who were not supplemented.
Discussion Vitamin D is known to play a role in the regulation of innate immune responses.1 Observational studies indicate that vitamin D deficiency may contribute to increased risk of ALRTI4–6,8 which is an important cause of morbidity and mortality in childhood,
Table 1 Regression model using serum 25(OH)D concentration as the dependent variable Variable
Co-efficient (b)
SE
t-value
P-value
Intercept % BSA exposed Vit. D supplements? No vs yes
58.64 0.35 213.97
7.64 0.16 5.24
7.68 2.23 22.66
,0.001 0.028 0.009
SE, standard error; BSA, body surface area.
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especially in developing countries.10 In this case– control study of the association between ALRTI and vitamin D status, there was no statistically significant difference in vitamin D status between cases and controls. Mean serum 25(OH)D concentration was . 50 nmol/L, the target level recommended by the American Academy of Pediatrics20 but ,75 nmol/L, which is considered insufficient by the USA’s Endocrine Society.22 Six previous case–control studies4–8 including one from Nigeria13 on the association between ALRTI and vitamin D status yielded different results, depending on the prevalence and severity of vitamin D deficiency in the study population (Table 2). The studies with low mean 25(OH)D concentrations in the range of 22.8–40.8 nmol/L and very high prevalence of vitamin D deficiency [serum 25(OH)D ,50 nmol/L] ranging from 79.4 to 87.5% found an increased risk of ALRTI in association with vitamin D deficiency.4–6 Studies with higher mean serum 25(OH)D concentrations ranging from 61.5 to 130.0 nmol/L and a lower prevalence of vitamin D deficiency (serum 25(OH)D ,50 nmol/L) ranging from 3.1 to 25% did not find an association between vitamin D status and the risk of ALRTI.7,8,13 The lack of association between ALRTI and vitamin D status in the latter studies relate to the lower prevalence of vitamin D deficiency compared with former studies which found an association.4–6 One Canadian study8 reported an association between severe ALRTI requiring admission to a paediatric intensive care unit and serum 25(OH)D concentrations ,50 nmol/L, categorised as deficient, or ,75 nmol/L, categorised as insufficient by the authors. In recent studies, vitamin D deficiency was
reported to be common in sick children admitted to paediatric intensive care units in Canada and the USA23,24 and was associated with greater disease severity.23 In a previous study from Nigeria13 with a smaller sample size, the authors found higher mean 25(OH)D concentrations in both cases (104 nmol/L) and controls (130 nmol/L) than in the present study. Among 25 subjects with ALRTI, three with pneumonia and empyema and two who had died from severe pneumonia had serum 25(OH)D concentrations ,70 nmol/L while none of the other patients with serum 25(OH)D concentrations .70 nmol/L died or developed empyema.13 In our study, there was no significant difference in mean 25(OH)D concentrations between four cases categorised as having severe disease and the other subjects with ALRTI requiring hospitalisation [65.9 (28.3) vs 63.1 (22.9) nmol/L]. Taken together, the number of cases categorised as severe disease in the two Nigerian studies was too small to investigate the association between severity of ALRTI and vitamin D status. In evaluating the factors associated with ALRTI, a lower percentage of BSA exposed to sunlight while outdoors was associated with increased odds of ALRTI by both univariate and logistic regression analysis. An Indian study5 which evaluated infant exposure to sunlight found by univariate analysis that not swaddling infants when exposed to sunshine outdoors was associated with a decreased risk of ALRTI. In that study, the percentage of cases not swaddled when exposed to outdoor sunlight among infants with ALRTI was 21% compared with 46% among controls without ALRTI (OR 0.31, CI 0.13– 0.73, P50.006). If confirmed by other studies, the findings will raise the interesting possibility of a direct
Table 2 Mean serum 25(OH)D concentration and risk of acute lower respiratory tract infection in infants and children in case–control studies Mean serum 25(OH)D concentration, nmol/L Country, ref. no.
Mean age, mths
India5
23.9 6
Turkey
0.3 (newborns)
Cases (n)
Controls (n)
22.8 (80)
38.4 (70)
22.8 (25)
40.8 (15)
Canada7
13.3
77.0 (64)
77.2 (65)
Canada8
13.6
81.0 (105)
83.0 (92)
4.2
29.2 (25)
39.2 (25)
20.5
104.0 (24)
130.0 (10)
13.0
61.5 (50)
63.1 (50)
Bangladesh4 Nigeria13
PICU, paediatric intensive care unit.
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Findings Severe ALRTI decreased by 99% if serum 25(OH)D .22.5 nmol/L 4-fold increased risk of ALRTI if serum 25(OH)D ,25 nmol/L Risk of admission for ALRTI not associated with vit. D status 8-fold increased risk of PICU admission with ALRTI if serum 25(OH)D ,50 nmol/L ALRTI decreased by 50% for each 10-nmol/L increase in serum 25(OH)D No significant difference in vit. D status between ALRTI cases and controls Vit. D status not associated with risk of admission for ALRTI
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biological effect of sunlight exposure on immune response and susceptibility to infection.25 This study also evaluated the risk factors for vitamin D deficiency in all the subjects to understand the factors which contribute to low vitamin D in the study population. Twenty-five per cent of all the subjects were vitamin D-deficient (serum 25(OH)D concentration ,50 nmol/L). Based on the reported risk factors for low vitamin D in childhood,26 the variables evaluated included gender, age, duration of exclusive breastfeeding, parental education and religion, type of housing, vitamin D supplementation, duration of exposure to sunlight and the percentage of BSA exposed while outdoors. Compared with children with serum 25(OH)D .50 nmol/L, younger age, lack of vitamin D supplementation and lower duration of sunlight exposure were independent factors by univariate analysis associated with serum 25(OH)D concentrations ,50 nmol/L. However, by multiple regression analysis, percentage BSA exposed to sunlight while outdoors and vitamin D supplementation were the only factors significantly associated with serum 25(OH)D concentration. Children who received vitamin D supplements had almost 14 nmol/L higher serum 25(OH)D concentrations than those who did not. Furthermore, there was a 3.5 nmol/L increase in serum 25(OH)D concentration for each 10% increase in BSA exposed to sunlight outdoors. This finding supports the role of adequate skin exposure to sunlight27 or vitamin D supplementation in preventing vitamin D deficiency when sun exposure is limited. The strength of this study is that adequate data were collected prospectively for all cases and controls to assess the association between ALRTI requiring hospitalisation and vitamin D status, taking other confounding variables into consideration. However, there are limiting factors. The wide age range enrolled could have affected the vitamin status of the study population. In addition, sunlight exposure was evaluated by sunlight exposure behaviour in the 7 days preceding the interview. This might not accurately reflect sun exposure in the children with ALRTI whose outdoor activities might have altered in the period leading up to admission with ALRTI. A history of the usual type of clothing before illness would have been more accurate. However, the mean duration of sunlight exposure was not significantly different between cases and controls. Also, the sample size was not adequate to assess the association between severity of ALRTI and vitamin D status. Although the vitamin D status of children requiring hospitalisation for ALRTI was not lower than that of controls, there was an association with sun exposure. There is vitamin D deficiency in this population, and sun exposure and vitamin D
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supplementation are important contributors to vitamin D status.
References 1 Bikle D. Nonclassic actions of vitamin D. J Clin Endocrinol Metab. 2009;94:26–34. 2 Liu PT, Stenger S, Li H, Wenzel L, Tan BH, Krutzik SR, et al. Toll-like receptor triggering of a vitamin D-mediated human antimicrobial response. Science. 2006;311:1770–3. 3 Walker VP, Modlin RL. The vitamin D connection to pediatric infections and immune function. Pediatr Res. 2009;65:106R–13R. 4 Roth DE, Shah R, Black RE, Baqui AH. Vitamin D status and acute lower respiratory infection in early childhood in Sylhet, Bangladesh. Acta Paediatr. 2010;99:389–93. 5 Wayse V, Yousafzai A, Mogale K, Filteau S. Association of subclinical vitamin D deficiency with severe acute lower respiratory infection in Indian children under 5 y. Eur J Clin Nutr. 2004;58:563–7. 6 Karatekin G, Kaya A, Salihoglu O, Balci H, Nuhoglu A. Association of subclinical vitamin D deficiency in newborns with acute lower respiratory infection and their mothers. Eur J Clin Nutr. 2009;63:473–7. 7 Roth DE, Jones AB, Prosser C, Robinson JL, Vohra S. Vitamin D status is not associated with the risk of hospitalization for acute bronchiolitis in early childhood. Eur J Clin Nutr. 2009;63:297–9. 8 McNally JD, Leis K, Matheson LA, Karuananyake C, Sankaran K, Rosenberg AM. Vitamin D deficiency in young children with severe acute lower respiratory infection. Pediatr Pulmonol. 2009;44:981–8. 9 Rudan I, Tomaskovic L, Boschi-Pinto C, Campbell H. Global estimate of the incidence of clinical pneumonia among children under five years of age. Bull WHO. 2004;82:895–903. 10 Black RE, Cousens S, Johnson HL, Lawn JE, Rudan I, Bassani DG, et al. Global, regional, and national causes of child mortality in 2008: a systematic analysis. Lancet. 2010;375:1969–87. 11 Oginni LM, Worsfold M, Oyelami OA, Sharp CA, Powell DE, Davie MW. Etiology of rickets in Nigerian children. J Pediatr. 1996;128:692–4. 12 Thacher TD, Fischer PR, Pettifor JM, Lawson JO, Isichei CO, Chan GM. Case-control study of factors associated with nutritional rickets in Nigerian children. J Pediatr. 2000;137: 367–73. 13 Oduwole AO, Renner JK, Disu E, Ibitoye E, Emokpae E. Relationship between vitamin D levels and outcome of pneumonia in children. West Afr J Med. 2010;29:373–8. 14 Lanata CF, Rudan I, Boschi-Pinto C, Tomaskovic L, Cherian T, Weber M, et al. Methodological and quality issues in epidemiological studies of acute lower respiratory infections in children in developing countries. Int J Epidemiol. 2004;33: 1362–72. 15 Dawodu A, Zalla L, Woo JG, Herbers PM, Davidson BS, Heubi JE, et al. Heightened attention to supplementation is needed to improve the vitamin D status of breastfeeding mothers and infants when sunshine exposure is restricted. Matern Child Nutr. 2012. DOI 10.1111/j.1740-8709.2012. 00422.x: 16 Barger-Lux MJ, Heaney RP. Effects of above average summer sun exposure on serum 25-hydroxyvitamin D and calcium absorption. J Clin Endocrinol Metab. 2002;87:4952–6. 17 Dawodu A, Absood G, Patel M, Agarwal M, Ezimokhai M, Abdulrazzaq Y, et al. Biosocial factors affecting vitamin D status of women of childbearing age in the United Arab Emirates. J Biosoc Sci. 1998;30:431–7. 18 Specker BL, Valanis B, Hertzberg V, Edwards N, Tsang RC. Sunshine exposure and serum 25-hydroxyvitamin D concentrations in exclusively breast-fed infants. J Pediatr. 1985;107:372–6. 19 World Health Organization Multicentre Growth Reference Study Group. WHO Child Growth Standards: length/heightfor-age, weight-for-age, weight-for-length, weight-for-height and body mass index-for-age: methods and development. Geneva: WHO, 2006. 20 Wagner CL, Greer FR. Prevention of rickets and vitamin D deficiency in infants, children, and adolescents. Pediatrics. 2008;122:1142–52. 21 Muhe L, Lulseged S, Mason KE, Simoes EA. Case-control study of the role of nutritional rickets in the risk of developing pneumonia in Ethiopian children. Lancet. 1997;349:1801–4.
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22 Holick MF, Binkley NC, Bischoff-Ferrari HA, Gordon CM, Hanley DA, Heaney RP, et al. Evaluation, treatment, and prevention of vitamin D deficiency: an Endocrine Society clinical practice guideline. J Clin Endocrinol Metab. 2011;96:1911–30. 23 McNally JD, Menon K, Chakraborty P, Fisher L, Williams KA, Al-Dirbashi OY, et al. The association of vitamin D status with pediatric critical illness. Pediatrics. 2012;130:429–36. 24 Madden K, Feldman HA, Smith EM, Gordon CM, Keisling SM, Sullivan RM, et al. Vitamin D deficiency in critically ill children. Pediatrics. 2012;130:421–8.
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25 Dowell SF. Seasonal variation in host susceptibility and cycles of certain infectious diseases. Emerg Infect Dis. 2001;7:369– 74. 26 Dawodu A, Wagner CL. Prevention of vitamin D deficiency in mothers and infants worldwide - a paradigm shift. Paediatr Int Child Health. 2012;32:3–13. 27 Dawodu A, Agarwal M, Hardy D, Kochiyil J. Contributions of sunshine deprivation and maternal vitamin D deficiency to rickets in the United Arab Emirates. Emirates Med J. 2006; 24:29–35.
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Department of Paediatrics, National Hospital Abuja, Abuja, Nigeria, 2Global Health Center, Cincinnati Children’s Hospital Medical Center/University of Cincinnati, Ohio, USA
Background: Acute lower respiratory tract infection (ALRTI) is the leading cause of childhood deaths in most developing countries, including Nigeria. Vitamin D is associated with innate immunity and may play a role in the control of infections. Case–control studies, including a small study from Nigeria, show inconsistent results for the association between vitamin D status and risk of ALRTI. Aims: To examine the relationship between vitamin D status and hospitalization for ALRTI in Nigerian children. Methods: Fifty children aged 2–60 months hospitalised with ALRTI were studied prospectively. ALRTI was diagnosed on the basis of modified WHO criteria. Each patient was matched with controls for age and gender. The controls were enrolled either from children attending well-child clinics or general clinics without evidence of respiratory infection or admitted to the hospital for elective surgery. A structured questionnaire collected data on demography, health, diet, duration of exposure to sunlight and percentage of body surface exposed to sunlight (according to type of clothing) while outdoors, and potential risk factors for ALRTI. Serum 25-hydroxyvitamin D [25(OH)D] concentration was measured using a chemiluminescenceimmuno-assay. The differences between cases and controls in serum 25(OH)D concentrations, association between vitamin D status and ALRTI and risk factors for vitamin D deficiency were assessed. Results: Mean (SD) 25(OH)D concentrations in patients and controls were similar [61.5 (25.8) vs 63.1 (22.9) nmol/L,P50.95].25% of all 100 subjects studied had serum 25(OH)D,50 nmol/L. In a multiple conditional logistic regression model, only lower percentage of body surface area exposed to sunlight was associated with increased risk of ALRTI. The percentage of body surface area exposed to sunlight while outdoors (P50.028) and vitamin D supplement use (P50.009) were independent determinants of vitamin D deficiency in the overall study population. Conclusions: ALRTI was not associated with vitamin D status, but was associated with less exposure to sunlight. Exposure to sunlight and vitamin D supplementation contributed to vitamin D status in this population. Keywords: Vitamin D, Lower respiratory infection, Children
Introduction The active metabolite of vitamin D (1,25-dihydroxyvitamin D) has been shown in both animal and invitro studies to be involved in innate immune responses.1 Recent in vitro studies demonstrate that vitamin D metabolites up-regulate the synthesis of intercellular antimicrobial peptide (cathelicidin) which is capable of killing micro-organisms and viruses.2 Vitamin D deficiency is linked to paediatric infections3 and a few case–control studies have reported associations
Correspondence to: P A Ahmed, Department of Paediatrics, National Hospital Abuja, Central District, PMB 425, Abuja, Nigeria. Email: [email protected]
ß W. S. Maney & Son Ltd 2014 DOI 10.1179/2046905514Y.0000000148
between vitamin D status and acute lower respiratory tract infections (ALRTI).4–8 A study from Bangladesh demonstrated an association between vitamin D deficiency and increased risk of ALRTI in early childhood.4 Other studies from India5 and Turkey6 linked vitamin D deficiency with severe ALRTI requiring hospitalisation. A study from Canada7 found no association between vitamin D status and the risk of hospitalisation for ALRTI, while another Canadian study found an association between serum 25-hydroxyvitamin D [25(OH)D],50 nmol/L (categorised as deficient) or ,75 nmol/L, (categorised as insufficient) and increased risk of severe pneumonia requiring intensive care.8 Together, these studies point
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to a possible contribution of vitamin D deficiency as a risk factor for ALRTI and support the theory that vitamin D supplementation could be a part of strategies to prevent childhood pneumonia. Acute lower respiratory tract infection, primarily pneumonia and bronchiolitis,9 is the leading cause of childhood deaths in most developing countries, including Nigeria.10 Although calcium deficiency has been suggested as an important cause of rickets in Nigerian children, vitamin D deficiency is the prevalent cause worldwide and also exists among Nigerian children with rickets.11,12 A study of children with rickets found an association with low calcium intake. However, 37% of the rachitic children had low vitamin D levels (serum 25(OH)D,30 nmol/L).12 Two studies from the Indian Sub-continent reported an increased risk of ARTI with low vitamin levels.4,5 Only one study with a small sample size has investigated the association between vitamin D status and ALRTI in Nigeria.13 The study compared 24 children hospitalized with pneumonia with ten controls and there was no significant difference in mean serum 25(OH)D concentrations between cases and controls. However, the authors reported that the two deaths and three cases of pneumonia complicated by empyema were associated with vitamin D insufficiency. The objective of this study was to examine the relationship between vitamin D status and the risk of hospitalisation for ALRTI.
At recruitment, each parent completed a structured questionnaire to collect data regarding parental education, religion, type of housing, exposure to smoke, immunisation, breastfeeding history, vitamin D supplementation, type of outdoor clothing and duration of exposure to sunlight in the week before interview or admission to hospital. Parents were asked about clothing covering the head, neck, face, arms, hands and legs while the child was outdoors. The total percentage of body surface area (BSA) exposed to sunlight was calculated using a formula for estimating BSA in children.15 The duration of skin exposure to sunlight and percentage BSA exposed to sunlight have been shown to correlate with vitamin D status in adults and children.16–18 Vitamin D supplement doses were calculated from the type and volume of vitamin syrup given to the infant. Weight and height were measured and each parameter was plotted on the WHO growth chart for children aged 0–5 years used by the institution, and a percentile recorded.19
Laboratory investigations On enrollment, 5 ml of venous blood was collected from each patient and control, and serum for measuring 25(OH)D concentrations was frozen at 220uC and shipped to Cincinnati Children’s Hospital, USA. The serum 25(OH)D concentration was determined using the DiaSorinLiaison 25(OH)D assay, according to manufacturer’s instructions. The intra- and inter-assay co-efficients of variation are ,8.5% and ,9.5%, respectively. Serum 25(OH)D concentration ,50 nmol/L, which is below the recommended target level for children, was categorized as vitamin D deficiency.20
Subjects and Methods This was a prospective study of 50 children aged 2– 60 months with ALRTI, recruited between November 2011 and September 2012 from the National Hospital, Abuja. There was a control for each case, matched for age and gender from the same location. Controls were enrolled either from children attending well-child clinics or general clinics without evidence of respiratory infections or admitted to the hospital for elective surgery. Controls were age-matched with cases to within 1 or 2 months. The admitting physicians diagnosed ALRTI on the basis of the modified WHO criteria which include a history of fever, cough, rapid breathing, lower chest-wall indrawing14 and/or abnormal auscultatory findings (crackles/crepitations or rhonchi, bronchial breath sounds), and radiological evidence of abnormal pulmonary parenchymal disease reported by a consultant radiologist. To exclude possible asthma, infants with bronchiolitis were those presenting with symptoms for the first time. Informed written or oral consent was obtained from the parents, and the study was approved by the National Hospital Abuja Ethics Committee.
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Sample size On the basis of the vitamin D status of Nigerian children with and without rickets12 and the reported higher rates of ALRTI in children with rickets,21 we extrapolated that children admitted with ALRTI would have a mean (SD) 25(OH)D of 34.8 (25.5) nmol/L, and that those without ALRTI would have a mean (SD) 25(OH)D of 51.3 (15.5) nmol/L. In order to detect this difference in means with a significance level of 0.05 and power of 90%, it was calculated that 36 children per group would be required. Allowing for a 30% rate of unexpected withdrawal or exclusion, 50 study subjects and 50 controls were enrolled.
Data analysis Summary descriptive socio-demographic, dietary and health statistics and vitamin D status of both groups were generated and all the variables were compared across cases and controls using a t-test if normally distributed. Continuous variables not normally distributed were compared across groups
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using a non-parametric test. Categorical variables were compared using x2 tests of association. The odds ratios for the association between ALRTI, serum 25(OH)D concentrations and other variables found to be significantly different between cases and controls were assessed using multiple conditional logistic regression. In a secondary analysis, the risk factors for vitamin D deficiency in the overall population of study children were investigated.
Results One hundred children aged between 2 and 60 months were recruited. Fifty children were admitted and treated for ALRTI (46 cases of pneumonia and four of bronchiolitis). Fifty children served as controls, as follows: 28 attending well-child clinics, 14 attending outpatient clinics with no history of respiratory disease, 7 with malarial fever, and one admitted for elective surgery. Mean (SD) age was similar between cases [12.9 (9.8) months] and controls [13.1 (10.5) months, P50.94]. Of the 100 infants enrolled, 56 were ,12 months, 28 were 12–24 months, 11 were 24–36 months, 4 were 36– 48 months and 2 were .48 months. Weight [8.4 (2.5) vs 9.1 (2.8) kg], months of exclusive breastfeeding [2.9 (2.6) vs 3.4 (2.3)], maternal post-secondary educational (62% vs 72%), western housing (94% vs 100%), hours of sunlight exposure per week [7.1 (9.1) vs 9.3 (13.4)], Islamic family religion (25% vs 34%), and use of vitamin D supplementation (20% vs 34%) were similar between cases and controls, respectively. Of the 27 infants who received vitamin D supplementation, 20 received 400 IU/day and 7 received 200 IU/day. Paternal post-secondary education (64% vs 80%), child’s mean (SD) weight for age [20.93 (1.39) vs 20.33 (1.43), P50.04] and weight for height [21.50 (2.15) vs 20.36 (2.24), P50.03] (Z-scores), and percentage BSA exposed to sunlight while outdoors [35% (16.0) vs 42% (13.0), P50.03] were significantly lower, respectively, in the cases than in the controls. Mean (SD) serum 25(OH)D concentrations were similar between cases and controls [61.5 (25.8) vs 63.1 (22.9) nmol/L, P50.95]. The difference in prevalence of vitamin D deficiency (serum 25(OH)D ,50 nmol/L) among cases (30%) and controls (20%) was not significant. The mean (SD) serum 25(OH)D concentration in samples (64) collected during the rainy season (April–October) and the dry season (36)
Respiratory infections and vitamin D
(November–March) [64.4 (23.2) vs 58.5 (26.4)] were not significantly different. In multiple conditional logistic regression, the only variable that significantly influenced the odds of ALRTI was the percentage of BSA exposed to sunlight. A 10% decrease in body surface area exposed to sunlight was associated with approximately 1.8 increased odds of ALRTI (OR 1.79, 95% CI 1.02–3.16). Two of the cases died and two additional subjects with ALRTI had severe pneumonia with pleural empyema requiring chest tube drainage. The mean serum 25(OH)D concentration in these four severe cases was not significantly different than in other patients with ALRTI [65.9 (28.3)vs 63.1 (22.9)].
Predictors of vitamin D nutrition Although there were no significant differences in vitamin D status between cases and controls, 25 (25%) of all the children recruited had serum 25(OH)D levels ,50 nmol/L.20 Secondary analysis assessed the risk factors for vitamin D deficiency in the overall study population. Univariate analysis found that younger patient age [8.5 (7.2) vs 14.5 (10.6) months, P50.004], weekly hours of sunlight exposure [5.1 (10.0) vs 9.3 (11.8), P50.026] and vitamin D supplementation (5% vs 25%, P50.018] were associated with serum 25(OH)Dlevels ,50 nmol/L. The following variables were included in regression analyses: vitamin D supplementation, hours of exposure to sunlight, percentage BSA exposed outdoors, age, family religion, maternal education, paternal education and months of exclusive breastfeeding. Only percentage BSA exposed to sunlight while outdoors (P50.028) and vitamin D supplementation (P50.009) were independent predictors of serum 25(OH)D concentrations (Table 1). For each 10% increase in BSA exposed to sunlight, serum 25(OH)D concentrations increased by 3.5 nmol/L. Children who received vitamin D supplementation had serum 25(OH)D concentration almost 14 nmol/L higher than those who were not supplemented.
Discussion Vitamin D is known to play a role in the regulation of innate immune responses.1 Observational studies indicate that vitamin D deficiency may contribute to increased risk of ALRTI4–6,8 which is an important cause of morbidity and mortality in childhood,
Table 1 Regression model using serum 25(OH)D concentration as the dependent variable Variable
Co-efficient (b)
SE
t-value
P-value
Intercept % BSA exposed Vit. D supplements? No vs yes
58.64 0.35 213.97
7.64 0.16 5.24
7.68 2.23 22.66
,0.001 0.028 0.009
SE, standard error; BSA, body surface area.
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especially in developing countries.10 In this case– control study of the association between ALRTI and vitamin D status, there was no statistically significant difference in vitamin D status between cases and controls. Mean serum 25(OH)D concentration was . 50 nmol/L, the target level recommended by the American Academy of Pediatrics20 but ,75 nmol/L, which is considered insufficient by the USA’s Endocrine Society.22 Six previous case–control studies4–8 including one from Nigeria13 on the association between ALRTI and vitamin D status yielded different results, depending on the prevalence and severity of vitamin D deficiency in the study population (Table 2). The studies with low mean 25(OH)D concentrations in the range of 22.8–40.8 nmol/L and very high prevalence of vitamin D deficiency [serum 25(OH)D ,50 nmol/L] ranging from 79.4 to 87.5% found an increased risk of ALRTI in association with vitamin D deficiency.4–6 Studies with higher mean serum 25(OH)D concentrations ranging from 61.5 to 130.0 nmol/L and a lower prevalence of vitamin D deficiency (serum 25(OH)D ,50 nmol/L) ranging from 3.1 to 25% did not find an association between vitamin D status and the risk of ALRTI.7,8,13 The lack of association between ALRTI and vitamin D status in the latter studies relate to the lower prevalence of vitamin D deficiency compared with former studies which found an association.4–6 One Canadian study8 reported an association between severe ALRTI requiring admission to a paediatric intensive care unit and serum 25(OH)D concentrations ,50 nmol/L, categorised as deficient, or ,75 nmol/L, categorised as insufficient by the authors. In recent studies, vitamin D deficiency was
reported to be common in sick children admitted to paediatric intensive care units in Canada and the USA23,24 and was associated with greater disease severity.23 In a previous study from Nigeria13 with a smaller sample size, the authors found higher mean 25(OH)D concentrations in both cases (104 nmol/L) and controls (130 nmol/L) than in the present study. Among 25 subjects with ALRTI, three with pneumonia and empyema and two who had died from severe pneumonia had serum 25(OH)D concentrations ,70 nmol/L while none of the other patients with serum 25(OH)D concentrations .70 nmol/L died or developed empyema.13 In our study, there was no significant difference in mean 25(OH)D concentrations between four cases categorised as having severe disease and the other subjects with ALRTI requiring hospitalisation [65.9 (28.3) vs 63.1 (22.9) nmol/L]. Taken together, the number of cases categorised as severe disease in the two Nigerian studies was too small to investigate the association between severity of ALRTI and vitamin D status. In evaluating the factors associated with ALRTI, a lower percentage of BSA exposed to sunlight while outdoors was associated with increased odds of ALRTI by both univariate and logistic regression analysis. An Indian study5 which evaluated infant exposure to sunlight found by univariate analysis that not swaddling infants when exposed to sunshine outdoors was associated with a decreased risk of ALRTI. In that study, the percentage of cases not swaddled when exposed to outdoor sunlight among infants with ALRTI was 21% compared with 46% among controls without ALRTI (OR 0.31, CI 0.13– 0.73, P50.006). If confirmed by other studies, the findings will raise the interesting possibility of a direct
Table 2 Mean serum 25(OH)D concentration and risk of acute lower respiratory tract infection in infants and children in case–control studies Mean serum 25(OH)D concentration, nmol/L Country, ref. no.
Mean age, mths
India5
23.9 6
Turkey
0.3 (newborns)
Cases (n)
Controls (n)
22.8 (80)
38.4 (70)
22.8 (25)
40.8 (15)
Canada7
13.3
77.0 (64)
77.2 (65)
Canada8
13.6
81.0 (105)
83.0 (92)
4.2
29.2 (25)
39.2 (25)
20.5
104.0 (24)
130.0 (10)
13.0
61.5 (50)
63.1 (50)
Bangladesh4 Nigeria13
PICU, paediatric intensive care unit.
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Findings Severe ALRTI decreased by 99% if serum 25(OH)D .22.5 nmol/L 4-fold increased risk of ALRTI if serum 25(OH)D ,25 nmol/L Risk of admission for ALRTI not associated with vit. D status 8-fold increased risk of PICU admission with ALRTI if serum 25(OH)D ,50 nmol/L ALRTI decreased by 50% for each 10-nmol/L increase in serum 25(OH)D No significant difference in vit. D status between ALRTI cases and controls Vit. D status not associated with risk of admission for ALRTI
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biological effect of sunlight exposure on immune response and susceptibility to infection.25 This study also evaluated the risk factors for vitamin D deficiency in all the subjects to understand the factors which contribute to low vitamin D in the study population. Twenty-five per cent of all the subjects were vitamin D-deficient (serum 25(OH)D concentration ,50 nmol/L). Based on the reported risk factors for low vitamin D in childhood,26 the variables evaluated included gender, age, duration of exclusive breastfeeding, parental education and religion, type of housing, vitamin D supplementation, duration of exposure to sunlight and the percentage of BSA exposed while outdoors. Compared with children with serum 25(OH)D .50 nmol/L, younger age, lack of vitamin D supplementation and lower duration of sunlight exposure were independent factors by univariate analysis associated with serum 25(OH)D concentrations ,50 nmol/L. However, by multiple regression analysis, percentage BSA exposed to sunlight while outdoors and vitamin D supplementation were the only factors significantly associated with serum 25(OH)D concentration. Children who received vitamin D supplements had almost 14 nmol/L higher serum 25(OH)D concentrations than those who did not. Furthermore, there was a 3.5 nmol/L increase in serum 25(OH)D concentration for each 10% increase in BSA exposed to sunlight outdoors. This finding supports the role of adequate skin exposure to sunlight27 or vitamin D supplementation in preventing vitamin D deficiency when sun exposure is limited. The strength of this study is that adequate data were collected prospectively for all cases and controls to assess the association between ALRTI requiring hospitalisation and vitamin D status, taking other confounding variables into consideration. However, there are limiting factors. The wide age range enrolled could have affected the vitamin status of the study population. In addition, sunlight exposure was evaluated by sunlight exposure behaviour in the 7 days preceding the interview. This might not accurately reflect sun exposure in the children with ALRTI whose outdoor activities might have altered in the period leading up to admission with ALRTI. A history of the usual type of clothing before illness would have been more accurate. However, the mean duration of sunlight exposure was not significantly different between cases and controls. Also, the sample size was not adequate to assess the association between severity of ALRTI and vitamin D status. Although the vitamin D status of children requiring hospitalisation for ALRTI was not lower than that of controls, there was an association with sun exposure. There is vitamin D deficiency in this population, and sun exposure and vitamin D
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supplementation are important contributors to vitamin D status.
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25 Dowell SF. Seasonal variation in host susceptibility and cycles of certain infectious diseases. Emerg Infect Dis. 2001;7:369– 74. 26 Dawodu A, Wagner CL. Prevention of vitamin D deficiency in mothers and infants worldwide - a paradigm shift. Paediatr Int Child Health. 2012;32:3–13. 27 Dawodu A, Agarwal M, Hardy D, Kochiyil J. Contributions of sunshine deprivation and maternal vitamin D deficiency to rickets in the United Arab Emirates. Emirates Med J. 2006; 24:29–35.
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