Table 2.
Determinants of vitamin D deficiency (25[OH]D <50 nmol/L): univariate and multivariate logistic regression analysis.
| Univariate Regression | Multiple Regression | |||||
|---|---|---|---|---|---|---|
| N | Percentage with 25(OH)D <50 nmol/L-N (%) | Crude Odds Ratio (95% CI) | p-Value | Adjusted Odds Ratio (95% CI) | p-Value | |
|
Sex *** Male Female |
||||||
| 854 | 52 (6.1%) | 1 (reference) | 0.03 | 1 (reference) | 0.09 | |
| 969 | 85 (8.8%) | 1.48 (1.04 to 2.12 | 1.49 (0.94 to 2.36) | |||
| Age at assent and screening (years) *** | ||||||
| 6 | 168 | 4 (2.4%) | 1.70 (1.46 to 1.98) | <0.001 | 1.25 (1.01 to 1.53) | 0.04 |
| 7 | 281 | 8 (2.9%) | ||||
| 8 | 346 | 18 (5.2%) | ||||
| 9 | 503 | 35 (7.0%) | ||||
| 10 | 396 | 48 (12.1%) | ||||
| 11+ | 108 | 22 (20.4%) | ||||
|
Ethnicity isiXhosa Colored Other * |
||||||
| 1756 | 135 (7.7%) | 1 (reference) | 0.08 | 1 (reference) | <0.001 | |
| 15 | 0 (0%) | - | 1 (-) | |||
| 17 | 1 (5.9%) | 0.75 (0.10 to 5.70) | 1.07 (0.11 to 9.91) | |||
| Season screened | ||||||
| January–March | 657 | 9 (1.4%) | 1 (reference) | <0.001 | 1 (reference) | <0.001 |
| April–June | 605 | 22 (3.6%) | 2.72 (1.24 to 5.95) | 1.59 (0.67 to 3.79) | ||
| July–September | 360 | 82 (22.8%) | 21.24 (10.52 to 42.87) | 10.69 (5.02 to 22.77) | ||
| October–December | 193 | 23 (11.9%) | 9.74 (4.43 to 21.44) | 6.73 (2.82 to 16.08) | ||
| Parental Level of Education ** | ||||||
| No formal education | 49 | 4 (8.2%) | 0.74 (0.47 to 1.17) | 0.20 | N/A | |
| Primary school level | 1504 | 119 (7.9%) | ||||
| Secondary school or higher | 271 | 15 (5.5%) | ||||
|
Household income (ZAR 1000 per month) |
||||||
| Q1 (0 – 0.76) | 416 | 37 (8.9%) | 0.98 (0.91 to 1.05) | 0.55 | N/A | |
| Q2 (0.78 – 1.2) | 407 | 30 (7.4%) | ||||
| Q3 (1.3 – 2.5) | 547 | 42 (7.7%) | ||||
| Q4 (2.6 – 45) | 454 | 29 (6.4%) | ||||
| Type of accommodation *** | ||||||
| Brick | 948 | 75 (7.9%) | 1 (reference) | 0.56 | N/A | |
| Informal | 876 | 63 (7.2%) | 0.90 (0.64 to 1.28) | |||
| Egg Consumption | ||||||
| Never | 27 | 1 (3.7%) | 1.11 (0.91 to 1.36) | 0.29 | N/A | |
| 1–4 times in past month | 210 | 13 (6.2%) | ||||
| 1–2 times per week | 850 | 66 (7.8%) | ||||
| 3–5 times per week | 565 | 42 (7.4%) | ||||
| Every day/almost every day | 172 | 16 (9.3%) | ||||
| Liver Consumption | ||||||
| Never | 86 | 6 (7.0%) | 1.13 (0.93 to 1.37) | 0.23 | N/A | |
| 1–4 times in past month | 790 | 50 (6.3%) | ||||
| 1–2 times per week | 655 | 58 (8.9%) | ||||
| 3–5 times per week | 241 | 21 (8.7%) | ||||
| Every day/almost every day | 52 | 3 (5.8%) | ||||
| Red Meat Consumption | ||||||
| Never | 112 | 7 (6.3%) | 0.91 (0.73 to 1.15) | 0.45 | N/A | |
| 1–4 times in past month | 1009 | 84 (8.3%) | ||||
| 1–2 times per week | 521 | 34 (6.5%) | ||||
| 3–5 times per week | 166 | 13 (7.8%) | ||||
| Every day/almost every day | 16 | 0 (0%) | ||||
| Fish Consumption | ||||||
| Never | 47 | 4 (8.5%) | 0.94 (0.81 to 1.09) | 0.41 | N/A | |
| Less than once a month | 204 | 14 (6.9%) | ||||
| 1–4 times in past month | 441 | 37 (8.4%) | ||||
| 1–2 times per week | 723 | 57 (7.9%) | ||||
| 3–5 times per week | 284 | 20 (7.0%) | ||||
| Every day/almost every day | 125 | 6 (4.8%) | ||||
| Margarine Consumption | ||||||
| Never | 17 | 0 (0%) | 0.84 (0.70 to 1.01) | 0.07 | 0.80 (0.62 to 1.04) | 0.10 |
| 1–4 times in past month | 59 | 8 (13.6%) | ||||
| 1–2 times per week | 127 | 15 (11.8%) | ||||
| 3–5 times per week | 462 | 36 (7.8%) | ||||
| Every day/almost every day | 1159 | 79 (6.8%) | ||||
| Anyone in household smokes cigarettes indoors | ||||||
| No | 1541 | 117 (7.6%) | 1 (reference)) | 0.92 | N/A | |
| Yes | 283 | 21 (7.4%) | 0.98 (0.60 to 1.58) | |||
| BMI-for-age Z-score *** | ||||||
| <−2 | 1155 | 81 (7.0%) | 1.15 (0.99 to 1.35) † | 0.08 | 1.24 (1.03 to 1.49) † | |
| +2 to +3 | 131 | 7 (5.3%) | ||||
| >+3 | 45 | 7 (15.2%) | ||||
| Time outside during daylight | ||||||
| <hour per day | 6 | 2 (33.3%) | 0.70 (0.43 to 1.15) ‡ | 0.16 | N/A | |
| 1–2 hours per day | 173 | 15 (8.7%) | ||||
| >2 hours per day | 1644 | 121 (7.4%) | ||||
| Amount of skin not covered when outdoors | ||||||
| Just face and hands | 166 | 16 (9.6%) | 0.72 (0.44 to 1.16) # # | 0.18 | N/A | |
| Arms/legs as well as face and hands | 1608 | 120 (7.5%) | ||||
| Often no shirt, as well as face, hands, arms, legs | 49 | 2 (4.1%) | ||||
| Time outside during daylight | ||||||
| <hour per day | 6 | 2 (33.3%) | 0.70 (0.43 to 1.15) ‡ | 0.16 | N/A | |
| 1–2 hours per day | 173 | 15 (8.7%) | ||||
| >2 hours per day | 1644 | 121 (7.4%) | ||||
| Sunscreen use | ||||||
| Usually | 41 | 0 (0%) | N/A | |||
| Not usually | 1782 | 138 (7.8%) | ||||
* Other included: Sotho (10), Venda (2), Shona (2), Swazi (1), Malawian (1) and Zimbabwean (1). ** Highest level of education of at least one parent. *** Missing data points: gender for two participants; age, 23; ethnicity, 37; parental level of education, one; type of housing, one; BMI (Z-score),1. † B-Coefficient represents reduction in 25(OH)D concentration (nmol/L) per unit increase of Z-score. ‡ B-Coefficient represents increase in 25(OH)D concentration (nmol/L) per additional extra hour spent outdoors during daylight hours. # B-Coefficient represents increase in 25(OH)D concentration (nmol/L) per category of increasing skin exposure when outdoors.