Millions of people take metformin to manage type 2 diabetes, but researchers wanted to know if this common medicine affects vitamin B12 levels. Scientists looked at 246 diabetes patients and found that those taking metformin had lower B12 levels overall, even though the number with serious deficiency wasn’t dramatically different. This study suggests that people on metformin should have their B12 checked regularly, especially if they’ve been taking the medicine for a long time. The findings highlight the importance of monitoring this vitamin to catch problems early and keep patients healthy.

The Quick Take

  • What they studied: Whether metformin, a popular diabetes medicine, causes people to have lower vitamin B12 levels
  • Who participated: 246 patients with type 2 diabetes at a hospital—some taking metformin and some not taking it
  • Key finding: People taking metformin had noticeably lower B12 levels (296 versus 382), but only 7.7% had serious deficiency compared to 4.8% in the non-metformin group—a difference that could have happened by chance
  • What it means for you: If you take metformin for diabetes, ask your doctor to check your B12 levels regularly, especially if you’ve been on the medicine for years. This simple blood test can catch problems early before you develop symptoms

The Research Details

Researchers looked back at medical records from 246 diabetes patients at one hospital to compare B12 levels between those taking metformin and those not taking it. This type of study is called a retrospective review—it’s like looking at old files instead of following people over time. The doctors measured B12 levels in everyone’s blood and defined deficiency as a level below 145 pmol/L (a standard measurement). They then used statistics to see if there was a real connection between metformin use and low B12.

This approach is useful for spotting patterns quickly and inexpensively, but it has limitations because researchers can’t control all the factors that might affect B12 levels. The study looked at one hospital only, so the results might not apply everywhere.

Understanding whether common diabetes medicines affect vitamin B12 is important because B12 deficiency can cause serious problems like nerve damage, weakness, and memory issues. If doctors know metformin might lower B12, they can watch for it and prevent these complications. This study helps fill a gap in what we know about long-term effects of this widely-used medicine.

This study has some strengths: it included a decent number of patients (246) and measured actual B12 blood levels. However, it has important limitations. It only looked at one hospital, so results might not apply to other places. The study didn’t track patients over time, so we can’t say for sure that metformin caused the lower B12—other factors could be involved. The researchers also didn’t provide details about how long people had been taking metformin or other medicines they were using, which could affect results.

What the Results Show

The study found that people taking metformin had B12 levels that were significantly lower on average (296 compared to 382). To put this in perspective, imagine two groups of students taking a test—one group averaged 296 points while the other averaged 382 points. That’s a real difference.

However, when the researchers looked at how many people actually had serious B12 deficiency (below the danger threshold), the numbers were closer: 7.7% of metformin users versus 4.8% of non-users. This difference of about 3% could have happened just by chance, which is why the researchers said it wasn’t statistically significant.

Think of it like this: metformin users definitely had lower B12 levels overall, but not all of them had a serious problem. The study suggests that metformin may gradually lower B12, but it doesn’t always cause a full deficiency.

The study didn’t report many other outcomes, but the main message was clear: B12 levels were consistently lower in the metformin group. This pattern held true even though the number of people with actual deficiency wasn’t dramatically different between groups.

Previous research has suggested that metformin might interfere with how the body absorbs B12, and this study supports that idea. The finding that metformin users have lower B12 levels aligns with what other scientists have found. However, some earlier studies showed bigger differences in deficiency rates, so this research adds nuance by showing that the relationship is more complicated than a simple yes-or-no answer.

This study has several important limitations to consider. First, it only looked at one hospital, so the results might not apply to all communities or different populations. Second, researchers didn’t know how long each person had been taking metformin—some might have just started while others took it for years, which could affect results. Third, the study didn’t account for other factors that lower B12, like diet, age, or other medicines. Finally, because this was a retrospective study looking at old records, researchers couldn’t control the conditions like they could in an experiment. These limitations mean we should be cautious about applying these findings to everyone.

The Bottom Line

If you take metformin for type 2 diabetes, talk to your doctor about checking your B12 levels regularly—especially if you’ve been on the medicine for more than a few years. This is a simple blood test that can catch problems early. If your B12 is low, your doctor might recommend supplements or dietary changes. This recommendation has moderate confidence because the study shows a real pattern, but more research is needed to understand exactly how much metformin affects B12 in different people.

Anyone taking metformin for diabetes should pay attention to this research. It’s especially important for people who have been on metformin for years. People with vegetarian or vegan diets should be extra careful since they get less B12 from food. Older adults should also be aware because they naturally absorb B12 less efficiently. However, this doesn’t mean you should stop taking metformin—it’s still an important medicine—just that you should monitor your B12.

B12 deficiency usually develops slowly over months or years, not overnight. If you start taking metformin, your B12 levels might begin dropping within weeks, but serious deficiency symptoms usually take months or years to appear. This is why regular monitoring is important—catching low B12 early prevents problems before they start.

Want to Apply This Research?

  • Set a reminder to log your B12 test results every 6-12 months if you take metformin. Track the actual number (like 296 or 382) rather than just ’normal’ or ’low’ so you can see if your levels are trending downward over time
  • Use the app to track B12-rich foods you eat (eggs, fish, dairy, fortified cereals) and set a goal to include them daily. If your doctor recommends a B12 supplement, log when you take it to build the habit and track consistency
  • Create a long-term health dashboard that shows your B12 test results over years alongside your metformin use. This helps you and your doctor spot patterns and decide if you need supplements or dietary changes

This research describes an association between metformin use and lower B12 levels, but does not prove that metformin causes B12 deficiency in all users. This study was conducted at a single hospital and may not apply to all populations. If you take metformin, consult your healthcare provider about whether B12 monitoring is appropriate for you. Do not stop taking metformin or change your diabetes treatment based on this information. B12 supplementation should only be started under medical supervision. This summary is for educational purposes and should not replace professional medical advice.