Seasonal trend of weekly baseline (pre-randomization) total 25(OH)D (LC-MS/MS), Calcium and iPTH averages over the course of the study. Fitted curve was modeled as a linear function of sine and cosine terms with period of one year, adjusted for age, gender, race, BMI, smoking status, and latitude.
Based on a total of 7502 (25(OH)D), 7447 (Ca), and 7474 (iPTH) baseline measurements from subjects without non-randomized vitamin D or calcium supplements; red dots: weekly means based on 3 or less measurements.