Table 2. Stud ies reporting on the relationship between obesity and vitamin D deficiency (n = 10).
| Author and publication year | Study design | Country | Sample size (n) | Age range or mean age | Obesity definition | Outcome definition | Outcome identification | Covariates | Results | Study quality (based on NOS score) |
|---|---|---|---|---|---|---|---|---|---|---|
| Dylag et al. | Cross-sectional | Poland | 100 (55 girls) | 1–5 years | WHO growth reference charts | Optimal vitamin D levels: >30 ≤ 50 ng ml−1; suboptimal vitamin D levels: ≤30 ≥ 20 ng ml−1; vitamin D Deficiency: <20 ng ml−1 | Blood test/assay | Age | Significantly lower mean difference in vitamin D concentrations: 23.6 ± 10.8 obese, 26.6 ± 9.8 non-obese. | High risk of bias (4/8) |
| Elizondo-Montemayor et al. | Cross-sectional | Mexico | 198 (98 girls) | 9 years | WHO growth reference charts | Optimal vitamin D levels: ≥30 ng ml−1; vitamin D insufficiency: 21–29 ng ml−1; vitamin D deficiency: <20 ng ml−1 | Overnight fasting blood sample assessed using competitive immunolumi nometric direct assay | Skin phototype, physical activity, screen time, vitamin use, diet | Obese status increased the odds of vitamin D deficiency (OR 2.679; 95% CI 1.245–5.765) | Low risk of bias (6/8) |
| Ghergherechi et al. | Case control | Iran | 109 | 8.9 years | >95% centile for age and gender | <20 ng dl−1 vitamin D deficiency; <10 ng dl−1 severe vitamin D deficiency | Blood test/assay | Age, sex, height | Vitamin D deficiency obese group = 76.9%; non-obese = 42.1%. Severe vitamin D deficiency obese group = 44.2%; non-obese = 17.5% | High risk of bias (4/9) |
| Jazar et al. | Cross-sectional | Jordan | 200 (100 girls) | 3.3 years | CDC growth charts | Vitamin D insufficiency, from 15 to 20 ng ml−1; vitamin D deficiency, ≤15 ng ml−1; severe vitamin D deficiency ≤ 5 ng ml−1 | Blood test/assay | Duration of breastfeeding, duration of formula feeding, duration of outdoor physical activity, calcium intake and dietary vitamin D intake | Significantly lower mean serum vitamin D levels in obese participants compared with controls (obese serum vit D levels = 13.0 ± 2.5 v normal weight 25.4 ±0.6) | High risk of bias (4/8) |
| Lee et al. | Cross-sectional | South Korea | 1660 (756 girls) | 9 years | BMI ≥ 95th percentile for age and sex | <20 ng ml−1 vitamin D deficient | Blood collected after overnight fasting and 25(OH)D concentrations measured by chemiluminescent immunoassay | - | Obese status increased odds of having lower mean serum vitamin D levels | Low risk of bias (5/8) |
| Rockell et al. | Cross-sectional | New Zealand | 1585 (784 girls) | 5–14 years | IOTF cut-offs | Vitamin D deficient <17.5 nmol L−1; vitamin D insufficient: <37.5 nmol L−1 | Blood sample/assay | Age, ethnicity, latitude (North vs. South Island), season (‘summer’ vs. ‘winter’ months) | Both vitamin D deficiency and insufficiency were significantly associated with obese status | Low risk of bias (7/8) |
| Senaprom et al. | Cross-sectional | Thailand | 477 (239 girls) | 7.8 years | BMI-for-age Z score (BAZ) >3 SD above the median for children aged 3–5.9 years (WHO, 2006) and as a BAZ > 2 SD above the median for children aged 6–13 years |
Vitamin D deficiency <50 nmol l−1 | Fasting blood sample analysed by chemiluminescence immunoassay | - | Obese status was significantly associated with vitamin D deficiency | Low risk of bias (5/8) |
| Tolppanen et al. | Prospective cohort | United Kingdom | 7555 (3744 girls) | 9.8 years | Cole et al. international BMI cut-off values | Vitamin D deficiency < 20 ng ml−1 | Non-fasting blood samples assayed using HPLC tandem mass spectrometry | - | Odds of vitamin D deficiency in obese participants was 1.49 (95% CI 1.01–2.20) | Low risk of bias (7/9) |
| Zhang et al. | Cross-sectional | China | 1488 (656 girls) | 8.8 years | Chinese obesity task force cut-off values | Vitamin D deficiency = <20 ng ml−1; vitamin D insufficiency = 20–30 ng ml−1: vitamin D sufficiency ≥ 30 ng ml−1 | Blood sample and liquid chromatography | Age, gender, dietary energy intake, energy expenditure | Significantly higher prevalence of vitamin D deficiency among obese participants compared with normal weight | Low risk of bias (7/8) |
| Zhou et al. | Cross-sectional | Australia | 221 (105 girls) | 1–5 years | WHO growth reference charts | Deficiency = vit D < 30 nmol L−1; insufficiency = Vit D ≥ 30 and <50 nmol L−1 | Non-fasting blood sample and assay | - | No significant difference between mean serum vitamin D levels in obese and normal weight individuals | Low risk of bias (6/8) |
Abbreviations: BMI, body mass index; CDC, Centers for Disease Control and Prevention; HPLC, high-performance liquid chromatography; IOTF, International Obesity Task Force; NOS, Newcastle–Ottawa Scale.