DESIGN: This is a cross-sectional study among Form 1 (year 7) students from 15 schools selected using a stratified random sampling design. Information regarding sociodemographic characteristics, clinical data and environmental factors was collected and blood samples were taken for total vitamin D. Descriptive and multivariable logistic regression was performed on the data.
SETTING: National secondary schools in Peninsular Malaysia.
PARTICIPANTS: 1361 students (mean age 12.9±0.3 years) (61.4% girls) completed the consent forms and participated in this study. Students with a chronic health condition and/or who could not understand the questionnaires due to lack of literacy were excluded.
MAIN OUTCOME MEASURES: Vitamin D status was determined through measurement of sera 25-hydroxyvitamin D (25(OH)D). Body mass index (BMI) was classified according to International Obesity Task Force (IOTF) criteria. Self-reported physical activity levels were assessed using the validated Malay version of the Physical Activity Questionnaire for Older Children (PAQ-C).
RESULTS: Deficiency in vitamin D was seen in 78.9% of the participants. The deficiency was significantly higher in girls (92.6%, p<0.001), Indian adolescents (88.6%, p<0.001) and urban-living adolescents (88.8%, p<0.001). Females (OR=8.98; 95% CI 6.48 to 12.45), adolescents with wider waist circumference (OR=2.64; 95% CI 1.65 to 4.25) and in urban areas had higher risks (OR=3.57; 95% CI 2.54 to 5.02) of being vitamin D deficient.
CONCLUSIONS: The study shows a high prevalence of vitamin D deficiency among young adolescents. Main risk factors are gender, ethnicity, place of residence and obesity.
OBJECTIVES: To investigate the hypothesis that vitamin D supplementation increases serum 25-hydroxyvitamin D level in children and adults with sickle cell disease.To determine the effects of vitamin D supplementation on general health such as growth status and health-related quality of life; on musculoskeletal health including bone mineral density, pain crises, bone fracture and muscle health; on respiratory health which includes lung function tests, acute chest syndrome, acute exacerbation of asthma and respiratory infections; and the safety of vitamin D supplementation in children and adults with sickle cell disease.
SEARCH METHODS: We searched the Cochrane Haemoglobinopathies Trials Register, compiled from electronic database searches and handsearching of journals and conference abstract books. We also searched database such as PubMed, clinical trial registries and the reference lists of relevant articles and reviews.Date of last search: 15 December 2016.
SELECTION CRITERIA: Randomised controlled studies and quasi-randomised controlled studies (controlled clinical studies) comparing oral administration of any form of vitamin D supplementation to another type of vitamin D or placebo or no supplementation at any dose and for any duration, in people with sickle cell disease, of all ages, gender, and phenotypes including sickle cell anaemia, haemoglobin sickle cell disease and sickle beta-thalassaemia diseases.
DATA COLLECTION AND ANALYSIS: Two authors independently extracted the data and assessed the risk of bias of the included study. They used the GRADE guidelines to assess the quality of the evidence.
MAIN RESULTS: One double-blind randomised controlled study including 46 people with sickle cell disease (HbSS, HbSC, HbSβ+thal and HbSβ0thal) was eligible for inclusion in this review. Of the 46 enrolled participants, seven withdrew before randomisation leaving 39 participants who were randomised. Only 25 participants completed the full six months of follow up. Participants were randomised to receive oral vitamin D3 (cholecalciferol) (n = 20) or placebo (n = 19) for six weeks and were followed up to six months. Two participants from the treatment group have missing values of baseline serum 25-hydroxyvitamin D, therefore the number of samples analysed was 37 (vitamin D n = 18, placebo n = 19).The included study had a high risk of bias with regards to incomplete outcome data (high dropout rate in the placebo group), but a low risk of bias for other domains such as random sequence generation, allocation concealment, blinding of participants, personnel and outcome assessors, selective outcome reporting; and an unclear risk of other biases.Compared to the placebo group, the vitamin D group had significantly higher serum 25-hydroxyvitamin D (25(OH)D) levels at eight weeks, mean difference 29.79 (95% confidence interval 26.63 to 32.95); at 16 weeks, mean difference 12.67 (95% confidence interval 10.43 to 14.90); and at 24 weeks, mean difference 15.52 (95% confidence interval 13.50 to 17.54). We determined the quality of the evidence for this outcome to be moderate. There was no significant difference of adverse events (tingling of lips or hands) between the vitamin D and placebo groups, risk ratio 3.16 (95% confidence interval 0.14 to 72.84), but the quality of the evidence was low. Regarding the frequency of pain, the vitamin D group had significantly fewer pain days compared to the placebo group, mean difference -10.00 (95% confidence interval -16.47 to -3.53), but again the quality of the evidence was low. Furthermore, the review included physical functioning PedsQL scores which was reported as absolute change from baseline. The vitamin D group had a lower (worse) health-related quality of life score than the placebo group but this was not significant at eight weeks, mean difference -2.02 (95% confidence interval -6.34 to 2.30). However, the difference was significant at both 16 weeks, mean difference -12.56 (95% confidence interval -16.44 to -8.69) and 24 weeks, mean difference -12.59 (95% confidence interval -17.43 to -7.76). We determined the quality of evidence for this outcome to be low.
AUTHORS' CONCLUSIONS: We included only one low-quality clinical study which had a high risk of bias with regards to incomplete outcome data. Therefore, we consider that the evidence is not of sufficient quality to guide clinical practice. Until further evidence becomes available, clinicians should consider the relevant existing guidelines for vitamin D supplementation (e.g. the Endocrine Society Clinical Practice Guidelines) and dietary reference intakes for calcium and vitamin D (e.g. from the USA Institute of Medicine). Evidence of vitamin D supplementation in sickle cell disease from high quality studies is needed. Well-designed, randomised, placebo-controlled studies of parallel design, are required to determine the effects and the safety of vitamin D supplementation in children and adults with sickle cell disease.