Date of Award


Level of Access

Campus-Only Dissertation

Degree Name

Doctor of Philosophy (PhD)


Food and Nutrition Sciences


Susan Sullivan

Second Committee Member

Adrienne White

Third Committee Member

Alfred Bushway


The purpose of this research was to assess the efficacy of three vitamin D supplementation protocols after Roux-en-Y gastric bypass surgery. The efficacy of supplementation was defined in terms of the nmol/L rise in serum 25-hydroxyvitamin D [25(OH)D] per one mcg oral supplementation and number of subjects achieving optimal serum 25(OH)D (>80 nmol/L) at twelve-months postoperative. Between November 2006 and December 2007, 47 subjects undergoing bariatric surgery, aged 21 to 62 years, enrolled in the study. Subjects with preoperative serum 25(OH)D levels >50 nmol/L received 1200 IU vitamin D3 daily. Deficient subjects (serum 25(OH)D levels/L) were randomized to receive 50,000 IU vitamin D2 weekly or 2800 IU vitamin D3 daily postoperatively. In addition, 1200 IU D3/day were provided from a multivitamin/mineral and calcium supplementation. The primary outcome measure was the change in serum 25(OH)D from preoperative to twelve-months postoperative. The mean preoperative 25(OH)D level for the non-deficient subjects (n=30) was 71.0 ± 15.6 nmol/L. The mean preoperative 25(OH)D level for the deficient subjects (n=17), was 40.1 ± 15.6 nmol/L. At twelve-months postoperatively, 72% of subjects taking 50,000 IU D2 weekly attained optimal vitamin D status. Fifty percent of subjects taking 2800 IU D3 daily and 50% of the subjects taking 1200 IU D3 daily achieved optimal vitamin D levels. The change in serum 25(OH)D from preoperative to twelve-months postoperative per mcg supplementation for all groups was as follows: 1200 IU D3/day: 0.61 ±1.6 nmol/L; 2800 IU D3/day (+ 1200 IU D3/day): 0.42 ± 0.27 nmol/L; 50,000 IU D2/week (+ 1200 IU D3/day): 0.32 ± 0.23 nmol/L. The efficacy of weekly vitamin D2 supplementation versus daily vitamin D3 supplementation (nmol/L increase in 25(OH)D per mcg supplemented) was not different. Both types of vitamin D can be used for vitamin D supplementation. All three supplementation protocols were less effective at raising 25(OH)D levels than expected. During vitamin D repletion after Roux-en-Y gastric bypass surgery, serum 25(OH)D levels should be monitored and vitamin D doses adjusted.