Scientists discovered that your genes play a big role in how well your body absorbs and uses vitamin B12, even when you eat enough of it. Researchers studied 104 healthy young adults in India and found that some people absorb B12 much better than others—up to 4 times better in some cases. They identified 85 genetic variations that affect B12 absorption, including 80 that were never found before. This discovery could help doctors identify people who need B12 supplements even if they’re eating the right amount of food, leading to personalized nutrition plans based on individual genetics.

The Quick Take

  • What they studied: How genetic differences affect the amount of vitamin B12 that your body actually absorbs and uses from food and supplements
  • Who participated: 104 healthy young adults living in India, ranging from young adults to middle-aged individuals without known health problems
  • Key finding: People’s genes significantly control how much B12 their bodies absorb—some people absorb more than 4 times as much as others. Scientists found 85 genetic variations linked to this difference, with 80 being completely new discoveries
  • What it means for you: If you have certain genetic variations, you might need B12 supplements even if you eat plenty of B12-rich foods. A simple genetic test might one day help doctors figure out if you’re one of these people, though this research is still early and more testing is needed before this becomes standard practice

The Research Details

Researchers gave 104 healthy Indian adults a special form of vitamin B12 labeled with a tracer (like a radioactive dye) so they could track exactly how much B12 their bodies absorbed over time. They measured B12 levels in the blood at different time points and used mathematical models to calculate how much B12 each person’s body actually used.

At the same time, they collected DNA samples and looked for genetic variations that might explain why some people absorbed more B12 than others. They examined 85 different genetic spots that are involved in how the body handles B12. They also created a genetic “score” by combining information from all these genetic variations to see if they could predict who would be good or poor B12 absorbers.

This approach is more precise than previous studies because it actually measured how much B12 was absorbed, rather than just looking at B12 levels in the blood, which can be affected by many other factors.

Previous studies only looked at how much B12 was in people’s blood, but that doesn’t tell the whole story about absorption. This study actually measured how much B12 the body took in and used, which is much more accurate. By doing this in a controlled way with a special labeled B12, the researchers could see the real differences between people and connect those differences to specific genes.

This study was published in a highly respected nutrition science journal. The researchers used precise laboratory methods to measure B12 absorption rather than relying on estimates. However, the study only included 104 people from one region of India, so the findings may not apply equally to all populations around the world. The study was well-designed with proper controls and statistical analysis, but it’s an early-stage discovery that needs confirmation in larger groups of people from different backgrounds.

What the Results Show

The study found that B12 bioavailability—the amount of B12 your body actually absorbs and uses—averaged 52% across all participants, meaning people absorbed about half of the B12 they consumed. However, there was huge variation: some people absorbed as little as 36% while others absorbed as much as 68%, showing a 4.4-fold difference between the best and worst absorbers.

The researchers identified 85 genetic variations associated with these differences in B12 absorption. Of these, 5 had been found in previous studies, but 80 were completely new discoveries. These genetic variations were located in or near 14 different genes that are known to be involved in B12 absorption and processing.

When the researchers combined all 85 genetic variations into a single genetic score, this score could explain 72% of the differences in B12 absorption among the study participants. In a separate test with different people, the genetic score explained 55% of the variation, which is still quite strong and suggests the findings are likely real.

The genetic score was also able to identify people at highest risk of poor B12 absorption who might need supplements, though the accuracy wasn’t perfect—it correctly identified about 32% of people who truly needed supplementation.

The study also measured two specific B12 markers in the blood: total B12 and holotranscobalamin (the form of B12 that your body can actually use). These measurements helped confirm that the genetic variations were truly affecting how the body handles B12, not just random differences in blood levels. The findings suggest that genetics influences both how much B12 is absorbed and how it’s transported and stored in the body.

This research builds on previous studies that found genetic links to B12 levels in the blood, but it goes further by actually measuring absorption rather than just blood levels. The 5 genetic variations that matched previous studies confirm that this research is on the right track. The 80 new genetic variations discovered here suggest that previous studies were only finding part of the genetic story, and there’s much more to learn about how genes control B12 absorption.

The study only included 104 people from India, so we don’t know if these same genetic variations affect B12 absorption in people from other parts of the world with different genetic backgrounds and diets. The study only looked at healthy young adults, so the findings might not apply to older people, children, or people with health conditions. The genetic score was very good at explaining B12 absorption in the same group of people who were studied, but it was less accurate when tested on a different group, suggesting it may need refinement. Finally, this is an early discovery study, and the genetic variations identified need to be confirmed in much larger populations before they could be used in clinical practice.

The Bottom Line

Based on this research, there is moderate evidence that genetic testing could one day help identify people who need B12 supplements even when eating adequate amounts. However, this is still experimental and not ready for routine clinical use. Current recommendations remain: eat B12-rich foods (meat, dairy, eggs, fortified cereals) or take supplements if you’re vegetarian, vegan, or over 50 years old. If you have symptoms of B12 deficiency (fatigue, weakness, numbness), ask your doctor for blood tests rather than relying on genetic testing alone.

This research is most relevant to people who are vegetarian or vegan, people over 50, people with digestive disorders, and people taking certain medications that affect B12 absorption. It may also be important for people with a family history of B12 deficiency. This research is less immediately relevant to people eating a typical diet with meat and dairy products, though it may become relevant in the future as genetic testing becomes more common. Healthcare providers and nutrition scientists should pay attention to this research as it develops.

If genetic testing for B12 absorption becomes available, it would likely take several months of consistent supplementation (if needed) to see improvements in energy levels and symptoms. However, this research is still in early stages—it will likely take 5-10 years of additional research before genetic testing could be offered routinely in clinical practice.

Want to Apply This Research?

  • Track B12 intake from food and supplements daily, and monitor energy levels and symptoms (fatigue, numbness, brain fog) weekly using a simple 1-10 scale to see if supplementation helps
  • If you’re at risk for B12 deficiency, set a daily reminder to take a B12 supplement or eat a B12-rich food, and log it in the app to build consistency
  • Create a monthly check-in where you review your B12 intake, energy levels, and any symptoms, and share this data with your healthcare provider at annual checkups to monitor your B12 status over time

This research is preliminary and describes early-stage discoveries about how genes affect B12 absorption. Genetic testing for B12 absorption is not yet available for routine clinical use and should not be used to replace standard medical evaluation. If you suspect you have a B12 deficiency, consult with your healthcare provider for proper testing and diagnosis. Do not start or stop B12 supplements without talking to your doctor first. This article is for educational purposes only and is not medical advice.