AIM 1: To determine if early administration of vitD3 (vs placebo) improves clinical outcomes in patients with low vitamin D status and severe sepsis. Hypothesis 1a: Early vitD3 decreases 90-day mortality after onset of severe sepsis (Primary Outcome). Hypothesis 1b: Early vitD3 decreases sequential organ failure assessment scores in the first 5 days after onset of severe sepsis. Hypothesis 1c: Early vitD3 decreases non-home discharge rate in those who survive severe sepsis.