Researchers studied 465 people who had a common weight loss surgery called sleeve gastrectomy to understand why some develop iron deficiency and anemia afterward. They found that women and people who already had anemia before surgery were more likely to develop these problems in the year following surgery. Interestingly, taking iron and vitamin B12 supplements at low doses didn’t significantly prevent these issues. The study suggests that doctors should pay special attention to certain patients before and after this surgery to catch and treat anemia early.

The Quick Take

  • What they studied: Whether certain characteristics of patients make them more likely to develop iron deficiency and anemia after sleeve gastrectomy weight loss surgery
  • Who participated: 465 people who had sleeve gastrectomy surgery between 2014 and 2021, with follow-up for one year after surgery
  • Key finding: About 1 in 10 patients developed iron deficiency or anemia within a year after surgery. Women were nearly 4 times more likely to develop these problems than men, and people who already had anemia before surgery were at higher risk. Low-dose iron supplements didn’t significantly prevent these problems.
  • What it means for you: If you’re considering or have had sleeve gastrectomy weight loss surgery, especially if you’re female or have a history of anemia, ask your doctor about monitoring your iron levels regularly. Standard low-dose supplements may not be enough, so your doctor may need to recommend higher doses or more frequent testing.

The Research Details

This was a retrospective cohort study, which means researchers looked back at medical records of people who had already undergone sleeve gastrectomy surgery. They examined 465 patients treated between April 2014 and December 2021 and followed their health for one year after surgery. The researchers identified which patients developed iron deficiency or anemia and looked for patterns in their characteristics before surgery.

Starting in December 2020, some patients received additional iron and vitamin B12 supplements after surgery, while earlier patients did not. This allowed the researchers to compare whether these supplements helped prevent anemia. The researchers used statistical analysis to identify which factors (like being female or having anemia before surgery) were most strongly linked to developing anemia afterward.

This research approach is important because it shows real-world outcomes in actual patients rather than controlled laboratory conditions. By looking back at detailed medical records, researchers could identify patterns that might help doctors predict which patients need closer monitoring or more aggressive treatment after weight loss surgery. Understanding these risk factors helps doctors provide better care and prevent complications.

This study has several strengths: it included a reasonably large number of patients (465), followed them for a full year, and used statistical methods to identify independent risk factors. However, it’s a retrospective study, meaning researchers relied on existing medical records rather than carefully controlling conditions as in a controlled experiment. The study was conducted at what appears to be a single medical center, so results may not apply equally to all populations. The supplement dosages used were relatively low, which may explain why they didn’t show significant benefit.

What the Results Show

Before surgery, about 22% of patients had iron deficiency and about 5% had iron deficiency anemia. One year after surgery, these numbers changed: iron deficiency dropped to about 11%, but iron deficiency anemia actually increased to about 11%. This suggests that while some patients improved, others developed new problems.

The researchers identified two main risk factors for developing anemia after surgery. Women were about 3.7 times more likely to develop iron deficiency or anemia compared to men. Patients who already had anemia before surgery were about 2.1 times more likely to develop these problems afterward. Interestingly, patients who started with higher iron saturation levels (a measure of how much iron their body was storing) were less likely to develop anemia after surgery.

When researchers looked at whether iron and vitamin B12 supplements helped, they found surprising results. Patients who took low-dose iron supplements (0.1 grams) and vitamin B12 (0.5 mg) daily had a 12% rate of iron deficiency or anemia one year after surgery. Patients who didn’t take supplements had a 12.6% rate. This difference was so small that it could easily be due to chance, suggesting the low-dose supplements didn’t provide meaningful protection.

The study also tracked anemia of chronic disease (a different type of anemia related to long-term inflammation) in some patients. Before surgery, about 4% of patients had this condition, and it increased slightly to about 7% after surgery. This suggests that weight loss surgery may trigger some inflammatory responses that affect blood health in multiple ways.

Previous research has shown that weight loss surgery can affect nutrient absorption and increase the risk of deficiencies. This study confirms that anemia is a real concern after sleeve gastrectomy and provides new information about which patients are at highest risk. The finding that low-dose supplements don’t significantly prevent anemia suggests that previous recommendations may need adjustment, and patients may need higher doses or more frequent monitoring than currently standard.

This study has several important limitations. First, it looked back at medical records rather than carefully controlling the study conditions, which can introduce errors or missing information. Second, the supplement doses used were relatively low, so the results don’t tell us whether higher doses might work better. Third, the study was conducted at one medical center, so results may differ in other populations or geographic areas. Fourth, not all patients had complete follow-up data, which could affect the results. Finally, the study couldn’t determine exactly why women had higher rates of anemia—it only showed that they did.

The Bottom Line

If you’re considering sleeve gastrectomy surgery, discuss iron and anemia screening with your doctor before the procedure, especially if you’re female or have a history of anemia (moderate confidence). After surgery, have your iron levels and blood counts checked regularly—at least at 6 months and 1 year, and possibly more frequently if you have risk factors (moderate to high confidence). If you develop iron deficiency or anemia after surgery, your doctor may need to recommend higher-dose supplements than the low doses studied here (moderate confidence). Don’t rely on standard multivitamins alone; work with your doctor to develop a personalized supplementation plan based on your individual needs.

This research is most relevant for people considering or who have recently had sleeve gastrectomy surgery, particularly women and those with a history of anemia. It’s also important for bariatric surgeons and primary care doctors who manage patients after weight loss surgery. People with other types of weight loss surgery may have different risks, so they should discuss their specific situation with their doctors.

Anemia can develop gradually over months after surgery. Most cases in this study appeared within the first year, so this is a critical period for monitoring. Some patients may develop problems sooner, while others may take longer, so regular check-ups throughout the first year are important. After one year, continued monitoring may still be needed, but the highest-risk period appears to be the first 12 months.

Want to Apply This Research?

  • Track your hemoglobin and iron saturation levels every 3 months for the first year after surgery, and every 6 months thereafter. Record the date, value, and whether you’re taking iron supplements. Set reminders for lab work appointments and supplement refills.
  • Set daily reminders to take iron and vitamin B12 supplements as prescribed by your doctor. If you’re experiencing symptoms like fatigue, shortness of breath, or dizziness, log these in the app and share with your healthcare provider. Work with your doctor to adjust supplement doses based on lab results rather than staying on a fixed low dose.
  • Create a dashboard showing your iron and hemoglobin trends over time. Set alerts if values drop below your target range. Track any symptoms that might indicate worsening anemia. Share this data with your bariatric surgeon and primary care doctor at each visit to guide treatment decisions.

This research describes what happened in one group of patients and should not be considered personal medical advice. If you are considering weight loss surgery, have had weight loss surgery, or are experiencing symptoms like fatigue or shortness of breath, consult with your doctor or bariatric surgeon. The findings about low-dose supplements not preventing anemia do not mean you should stop taking supplements—instead, work with your healthcare provider to determine the right dose and monitoring plan for your individual situation. This study was published in October 2025 and represents current research, but medical recommendations may evolve as new evidence emerges.