Background/Objectives: To estimate the long-term prevalence of the most common nutrient deficiencies following bariatric surgery. Methods: Consecutive patients who underwent bariatric surgery were followed for 10 years. Anthropometric measurements, laboratory tests, and comorbidities were assessed at baseline and during follow-up visits. Results: A total of 155 patients were included (74.2% women; mean age 43.6 ± 9.3 years; mean body mass index [BMI]: 41.9 kg/m²). Patients underwent either sleeve gastrectomy (SG, n = 112) or gastric bypass (GB, n = 43). Over a median follow-up period of 10 (10–12) years, BMI decreased by 7.4 ± 5.8 kg/m². In the GB group, serum iron levels decreased significantly, whereas in the SG group, a reduction was observed in total iron-binding capacity (TIBC). Serum calcium, phosphorus, and 25-hydroxyvitamin D3 levels increased during follow-up. The prevalence of deficiencies in iron (9.0% vs. 18.7%, p < 0.05), folic acid (1.3% vs. 11.6%, p < 0.001), and vitamin B12 (7.1% vs. 17.4%, p < 0.01) increased, while the prevalence of hypocalcemia and 25-hydroxyvitamin D3 deficiency decreased. Conclusions: A significant increase in the prevalence of iron, folic acid, and vitamin B12 deficiencies was observed over a 10-year follow-up after bariatric surgery. SG and GB appear to have different long-term effects on iron metabolism.

Background: The long-term follow-up studies investigating the risk of anemia and iron deficiency following bariatric procedures are scarce. This study aimed to determine the influence of body weight reduction and type of bariatric surgery on iron metabolism parameters. Methods: We included 138 consecutive patients who underwent bariatric surgery (120 underwent sleeve gastrectomy and 18 underwent other types of bariatric surgery) between 2010 and 2016. At baseline and at follow-up (median observation: 10 years), examination weight and height were measured, and blood samples for iron metabolism parameters were taken. Results: Red blood cells (4.75 [4.59–4.96] 10⁶/μL vs. 4.51 [4.25–4.83] 10⁶/μL, p < 0.0001), hemoglobin (14.0 [13.3–14.7] g/dL vs. 13.0 [12.1–14.3] g/dL, p < 0.0001), and folic acid (7.4 [5.9–10.4] ng/ml vs. 6.0 [4.5–9.1] ng/mL, p = 0.01) were significantly lower, while anemia prevalence (6.52% vs. 28.99%, p < 0.0001) was significantly higher at the follow-up examination compared to the baseline values. In contrast, iron concentration (86.5 [68.0–109.0] µg/dL vs. 86.5 [55.0–110.0] µg/dL, p = 0.42) and TIBC values (351 [326–391] µg/dL vs. 345 [5311–387] µg/dL, p = 0.08) did not change significantly. The multivariable regression analyses showed that the only factors independently related to the hemoglobin concentration change were initial hemoglobin concentration, age, and bariatric procedures other than sleeve gastrectomy. Similarly, in the multivariable logistic analysis, the only variables independently related to the risk of anemia were age (adjusted odds ratio 0.93 [95% confidence intervals 0.89–0.97]), initial hemoglobin concentration (0.69 [0.49–0.97]), and procedures other than sleeve gastrectomy bariatric procedures (6.12 [1.86–20.15]). Conclusions: Age, initial hemoglobin concentration, and type of bariatric procedure but not sex, baseline iron serum level, or weight change are related to the risk of anemia in the long-term follow-up following bariatric surgery.