Vitamin concentrations 5 years after gastric bypass. 
Few studies have investigated the effects of bariatric surgery on vitamin status in the long term.  We examined changes in vitamin status up to 5 years after Roux-en-Y gastric bypass surgery.  Using a retrospectively maintained database of patients undergoing weight loss surgery, we identified all patients operated with Roux-en-Y gastric bypass at our tertiary care hospital during July 2004-May 2008.  Data on vitamin concentrations and patient-reported intake of dietary supplements were collected up to July 2012.  Linear mixed models were used to estimate changes in vitamin concentrations during follow-up, adjusting for age and sex.  All patients were recommended daily oral multivitamin, calcium/vitamin D and iron supplements and 3-monthly intramuscular B-12 after surgery.  Out of the 443 patients operated with gastric bypass, we included 441 (99.5%) patients with one or more measurements of vitamin concentrations (75.1% women; mean age 41.5 years, mean body mass index 46.1 kg/m(2) at baseline).  At 5 years after surgery, the patients' estimated mean vitamin concentrations were either significantly higher (vitamin B-6, folic acid, vitamin B-12, vitamin C and vitamin A) or not significantly different (thiamine, 25-hydroxyvitamin D and lipid-adjusted vitamin E) compared with before surgery.  Use of multivitamin, calcium/vitamin D and vitamin B-12 supplements was reported by 1-9% of patients before surgery, 79-84% of patients at 1 year and 52-83% of patients 5 years after surgery.  In patients who underwent gastric bypass surgery, estimated vitamin concentrations were either significantly increased or unchanged up to 5 years after surgery.