Early changes in vitamin B12 uptake and biomarker status following Roux-en-Y gastric bypass and sleeve gastrectomy

Clin Nutr. 2019 Apr;38(2):906-911. doi: 10.1016/j.clnu.2018.02.007. Epub 2018 Feb 15.


Background & aims: Bariatric surgery increases the risk of micronutrient deficiencies, including vitamin B12 (B12) deficiency. We analysed early changes in biomarkers of B12 status following bariatric surgery.

Methods: We prospectively included adult patients (n = 27) referred for either Roux-en-Y Gastric Bypass (RYGB) (n = 19) or Sleeve Gastrectomy (SG) (n = 8). Blood samples were drawn before surgery and 2 and 6 months following surgery for measurement of B12, holotranscobalamin (holoTC), and methylmalonic acid (MMA). The B12 absorption capacity was estimated from the increase in plasma holoTC two days after a standardised oral B12 challenge.

Results: B12 status decreased following both RYBG and SG. While a decrease in plasma B12 was not evident until 6 months postoperatively, we observed a statistically significant decrease in plasma holoTC and increase in MMA already 2 months postoperatively. These changes were more pronounced at 6 months post surgery. Correspondingly, the B12 absorption capacity was decreased following surgery.

Conclusions: HoloTC and MMA were superior to B12 to detect early changes in B12 status following bariatric surgery. Our data challenge the current concept that liver B12 stores secure long-term maintenance of B12 status. They indicate that B12 treatment in pharmacological doses may be warranted immediately after surgery.

Keywords: Bariatric surgery; Homocysteine; Methylmalonic acid; Transcobalamins; Vitamin B12.

Publication types

  • Observational Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Aged
  • Avitaminosis
  • Biomarkers / blood
  • Biomarkers / metabolism
  • Female
  • Gastrectomy / adverse effects*
  • Gastric Bypass / adverse effects*
  • Homocysteine / blood
  • Humans
  • Male
  • Methylmalonic Acid / blood
  • Middle Aged
  • Obesity, Morbid / surgery
  • Postoperative Complications
  • Prospective Studies
  • Transcobalamins / analysis
  • Vitamin B 12 / blood*
  • Vitamin B 12 / metabolism*


  • Biomarkers
  • Transcobalamins
  • Homocysteine
  • Methylmalonic Acid
  • Vitamin B 12