Table 2.
Environmental factors are associated with vitamin D status
| 25(OH)D levels (nmol/L)a | Unadjusted regression analyses of 25(OH)D levels | Adjusted regression analyses of 25(OH)D levels | Adjusted logistic regression analyses 25(OH)D < 50 nmol/L | ||||||
|---|---|---|---|---|---|---|---|---|---|
| Medians (IQR) | Means (95% CI) | Beta (95% CI) | P | R2 | Beta (95% CI) | P | OR (95% CI) | P | |
| Age in years | - | - | − 0.05 (− 0.06, − 0.04) | < 0.0001 | 0.045 | − 0.07 (− 0.08, − 0.07) | < 0.0001 | 1.69 (1.52, 1.89) | < 0.0001 |
| Sex | |||||||||
| Males | 77.7 (64.1, 94.5) | 77.50 (76.52, 78.49) | Ref. | – | Ref. | – | Ref. | – | |
| Females | 77.2 (63.0, 94.0) | 76.45 (75.43, 77.48) | − 0.01 (− 0.03, 0.01) | 0.15 | 0.0005 | − 0.02 (− 0.03, 0.001) | 0.066 | 1.32 (1.04, 1.68) | 0.021 |
| Country | |||||||||
| Kenya | 81.0 (66.3, 101.6) | 81.85 (80.42, 83.30) | Ref. | – | Ref. | – | Ref. | – | |
| Uganda | 78.6 (65.1, 94.5) | 78.27 (77.02, 79.54) | − 0.04(− 0.07, − 0.02) | 0.0002 | 0.029 | 0.01 (− 0.02, 0.03) | 0.51 | 0.50 (0.34, 0.74) | 0.001 |
| Burkina Faso | 78.4 (64.5, 91.3) | 77.26 (74.98, 79.61) | − 0.06 (− 0.10, − 0.02) | 0.003 | − 0.05 (− 0.08, − 0.01) | 0.012 | 0.81 (0.45, 1.44) | 0.47 | |
| The Gambia | 71.2 (59.1, 84.2) | 72.78 (71.15, 74.45) | − 0.15 (− 0.18, − 0.12) | < 0.0001 | 0.09 (0.05, 0.13) | < 0.0001 | 0.29 (0.17, 0.47) | < 0.0001 | |
| South Africa | 76.2 (60.6, 91.9) | 70.39 (68.95, 71.86) | − 0.12 (− 0.14, − 0.09) | < 0.0001 | − 0.15 (− 0.18, − 0.12) | < 0.0001 | 2.89 (1.94, 4.29) | < 0.0001 | |
| Seasonb | |||||||||
| Summer/short rains/dry | 78.8 (64.8, 95.8) | 78.77 (77.19, 80.39) | Ref. | – | Ref. | – | Ref. | – | |
| Autumn/dry | 83.6 (67.1, 101.1) | 82.72 (81.43, 84.02) | 0.05 (0.02, 0.07) | 0.0002 | 0.038 | 0.03 (0.01, 0.06) | 0.014 | 0.65 (0.40, 0.96) | 0.032 |
| Winter/long rains | 73.3 (60.1, 87.0) | 71.14 (69.96, 72.34) | − 0.10 (− 0.13, − 0.08) | < 0.0001 | − 0.10 (− 0.12, − 0.07) | < 0.0001 | 2.55 (1.75, 3.72) | < 0.0001 | |
| Spring/dry | 76.3 (63.1, 91.4) | 75.18 (73.55, 76.84) | − 0.05 (− 0.08, − 0.02) | 0.002 | − 0.05 (− 0.08, − 0.02) | 0.002 | 1.60 (1.07, 2.38 | 0.022 | |
| Stuntingc | |||||||||
| Not stunted | 77.1 (63.7, 91.0) | 76.13 (75.08, 77.19) | Ref. | – | Ref. | – | Ref. | – | |
| Stunted | 73.1 (61.2, 88.4) | 73.58 (71.89, 75.31) | − 0.03 (− 0.06, − 0.01) | 0.015 | 0.003 | − 0.01 (− 0.04, 0.01) | 0.34 | 1.05 (0.69, 1.58) | 0.82 |
| Underweightd | |||||||||
| Not underweight | 77.2 (63.8, 91.7) | 76.67 (75.72, 77.64) | Ref. | – | Ref. | – | Ref. | – | |
| Underweight | 75.6 (61.9, 91.3) | 74.90 (72.68, 77.18) | − 0.02 (− 0.06, 0.01) | 0.15 | 0.0008 | − 0.004 (− 0.04, 0.03) | 0.81 | 0.88 (0.54, 1.40) | 0.58 |
| Wastinge> | |||||||||
| Not wasted | 76.0 (62.9, 90.6) | 75.32 (74.40, 76.26) | Ref. | – | Ref. | – | Ref. | – | |
| Wasted | 79.2 (63.6, 94.5) | 77.81 (74.45, 81.32) | 0.03 (− 0.02, 0.08) | 0.19 | 0.0008 | 0.04 (− 0.01, 0.08) | 0.12 | 0.64 (0.29, 1.38) | 0.25 |
| Inflammationf | |||||||||
| Without inflammation | 76.4 (62.7, 92.3) | 75.53 (74.74, 76.3) | Ref. | – | Ref. | – | Ref. | – | |
| With inflammation | 81.9 (68.0, 99.5) | 82.11 (80.55, 83.69) | 0.08 (0.06, 0.11) | < 0.0001 | 0.012 | 0.07 (0.05, 0.09) | < 0.0001 | 0.59 (0.43, 0.81) | 0.001 |
| Malariag | |||||||||
| Without malaria | 77.1 (63.1, 92.4) | 76.01 (75.26, 76.77) | Ref. | – | Ref. | – | Ref. | – | |
| With malaria | 71.3 (58.9, 85.4) | 71.63 (69.68, 73.63) | − 0.06 (− 0.09, − 0.03) | 0.0001 | 0.004 | − 0.04 (− 0.07, − 0.01) | 0.02 | 1.02 (0.65, 1.61) | 0.93 |
Correlation coefficients and p values were obtained from linear regression analyses and odds ratios from logistic regression analyses. 25(OH)D levels were ln-transformed in linear regression analyses to make them normally distributed. Covariates in the multivariable linear regression models included age, sex, season, inflammation and study site, as appropriate
25(OH)D 25-hydroxyvitamin D, n/a not available, OR odds ratio, 95% CI 95% confidence interval
aMedians (IQR) and geometric means are presented.bSeason was based on 3 monthly intervals. In South Africa, the seasons were summer, autumn, winter and spring; in Uganda and Kenya, there are two rainy seasons; and in Burkina Faso and The Gambia, there is a single rainy season. cStunting was defined as height-for-age Z score < − 2; dunderweight as weight-for-age Z score < − 2; ewasting as weight-for-height Z score < − 2; finflammation as CRP > 5 mg/L or ACT > 0.6 g/L and gmalaria as presence of P. falciparum parasites on blood film. Analyses by country are presented in Additional file 4: Table S3 (logistic regression) Additional file 5: Table S4 (unadjusted linear regression), and Additional file 6: Table S5 (adjusted linear regression)