Table 5: Evaluation of the parameters affecting the levels of vitamin D with linear regression analysis.
| I. | B | SE | T | P | CI 95% for β | |
| LL | UL | |||||
| Constant | -8.868 | 8.319 | -1.066 | 0.287 | -25.208 | 7.473 |
| Gender (male) | 3.932 | 0.793 | 4.957 | 0.001** | 2.374 | 5.49 |
| Age | 0.563 | 0.447 | 1.259 | 0.209 | -0.316 | 1.442 |
| Waist circumference | -0.136 | 0.058 | -2.332 | 0.020* | -0.25 | -0.021 |
| BMI | 0.543 | 0.164 | 3.311 | 0.001** | 0.221 | 0.865 |
| Habit (smoking) | 3.853 | 1.566 | 2.46 | 0.014* | 0.777 | 6.93 |
| Habit (alcohol) | 3.016 | 1.817 | 1.66 | 0.097 | -0.552 | 6.585 |
| Skin color | 0.364 | 0.619 | 0.588 | 0.557 | -0.851 | 1.579 |
| Time in sunny areas | 0.634 | 0.621 | 1.022 | 0.307 | -0.584 | 1.853 |
| Physical activity | 0.23 | 0.23 | 0.297 | 0.767 | -1.289 | 1.749 |
| Ca | 2.548 | 0.763 | 3.341 | 0.001** | 1.05 | 4.047 |
| ALP | -0.003 | 0.015 | -0.197 | 0.844 | -0.032 | 0.026 |
| PTH | -0.124 | 0.019 | -6.526 | 0.001** | -0.162 | -0.087 |
| II. | ||||||
| Constant | 19.973 | 11.841 | 1.687 | 0.093 | -3.339 | 43.285 |
| Age | 0.771 | 0.594 | 1.298 | 0.195 | -0.399 | 1.941 |
| Waist circumference | -0.036 | 0.091 | -0.392 | 0.695 | -0.215 | 0.144 |
| BMI | 0.248 | 0.15 | 1.65 | 0.1 | -0.048 | 0.544 |
| Habit | -2.334 | 0.975 | -2.394 | 0.017** | -4.253 | -0.415 |
| Skin color | -1.084 | 0.871 | -1.244 | 0.215 | -2.799 | 0.631 |
| Time in sunny areas | 0.375 | 1.3 | 0.288 | 0.773 | -2.186 | 2.935 |
| Physical activity | 0.329 | 0.444 | 0.74 | 0.46 | -0.546 | 1.203 |
| Clothing | -8.883 | 0.925 | -9.599 | 0.001** | -10.705 | -7.061 |
| Ca | 2.423 | 1.032 | 2.349 | 0.020** | 0.392 | 4.454 |
| ALP | -0.006 | 0.023 | -0.275 | 0.783 | -0.051 | 0.039 |
| PTH | -0.087 | 0.022 | -3.895 | 0.001** | -0.131 | -0.131 |
| III. | ||||||
| Constant | 27.24 | 3.373 | 8.077 | 0.001** | 20.603 | 33.877 |
| Age | -0.409 | 0.578 | -0.708 | 0.479 | -1.546 | 0.728 |
| Waist circumference | -0.157 | 0.065 | -2.401 | 0.017** | -0.286 | -0.028 |
| BMI | 0.616 | 0.195 | 3.158 | 0.002** | 0.232 | 0.999 |
| Habit | -0.68 | 0.533 | -1.275 | 0.203 | -1.73 | 0.37 |
| Skin color | 0.274 | 0.757 | 0.362 | 0.718 | -1.215 | 1.763 |
| Time in sunny areas | 2.27 | 2.398 | 0.947 | 0.345 | -2.45 | 6.99 |
| Physical activity | -0.631 | 0.613 | -1.03 | 0.304 | -1.836 | 0.575 |
| Ca | 0.817 | 0.946 | 0.863 | 0.389 | -1.045 | 2.678 |
| ALP | -0.006 | 0.018 | -0.362 | 0.718 | -0.041 | 0.028 |
| PTH | -0.129 | 0.03 | -4.276 | 0.001** | -0.189 | -0.07 |
I: Linear regression analysis with all subjects; II: Analysis with female students alone; III: Analysis with male students alone; Ca: Calcium; ALP: Alkaline phosphatase; PTH: Parathyroid hormone; BMI: Body mass index; Se: Standard Error; CI: Confidence Interval; LL: Lower Limit; UL: Upper Limit; *p < 0.05; **p < 0.01.