Anaemia in patients with self-reported use of iron supplements in the BAriatric surgery SUbstitution and nutrition study: A prospective cohort study

Background and aims: After bariatric surgery, micronutrient deficiencies may lead to anaemia. To prevent post-operative deficiencies, patients are recommended lifelong micronutrient supplementation. Studies investigating the effectiveness of supplementation to prevent anaemia after bariatric surgery are scarce. This study aimed to investigate the relationship between nutritional deficiencies and anaemia in patients who report use of supplementation two years after bariatric surgery versus patients who do not. Methods and results: Obese (BMI>35 kg/m2) individuals (n = 971) were recruited at Sahlgrenska University Hospital in Gothenburg, Sweden between 2015 and 2017. The interventions were Roux-en-Y gastric bypass (RYGB), n = 382, sleeve gastrectomy (SG), n = 201, or medical treatment (MT), n = 388. Blood samples and self-reported data on supplements were collected at baseline and two years post treatment. Anaemia was defined as haemoglobin <120 g/L for females and <130 g/L for males. Standard statistical methods, including a logistic regression model and a machine learning algorithm, were used to analyse data. The frequency of anaemia increased from baseline in patients treated with RYGB (3.0% vs 10.5%; p < 0.05). Neither iron-dependent biochemistry nor frequency of anaemia differed between participants who reported use of iron supplements and those who did not at the two-year follow-up. Low preoperative level of haemoglobin and high postoperative percent excessive BMI loss increased the predicted probability of anaemia two years after surgery. Conclusion: The results from this study indicate that iron deficiency or anaemia may not be prevented by substitutional treatment per current guidelines after bariatric surgery and highlights there is reason to ensure adequate preoperative micronutrient levels. Trial registration: March 03, 2015; NCT03152617.