Emulated Study of Vitamin D Correction Vs Non-Correction

Inclusion Criteria: * Any patient with at least one 25-OH vitamin D test result. Patients with one test result will remain in the limited dataset for potential future research. * Any patient with a 25-OH vitamin D level(s) always lower than 40 ng/ml (low level) with subsequent level(s) in the 40 ng/ml to 100 ng/ml range. The 40 ng/ml to 100 ng/ml range is maintained for three years. This corrected group is labeled as the Treatment Group. * Any patient with a 25-OH vitamin D level always lower than 40 ng/ml with maintenance of that lower than 40 ng/ml level for 3 years. This uncorrected group is labeled as Control Group A. * Any patient who has an uninterrupted 25-OH vitamin D level greater than or equal 40 ng/ml and less than or equal to 100 ng/ml (sufficient level) for a continuous 3-year period. Prior to the 3-year period there were no levels lower than 40ng/ml or higher than 100 ng/ml. This vitamin D3 sufficient group is labeled as Control Group B. Exclusion Criteria: * Any patient with only one 25-OH vitamin D3 test result or any patient who cannot be included in the Treatment Group, Control Group A, or Control Group B is excluded.