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The Connection Between Vitamin B12 Deficiency and Weight Gain

Here’s what the science says.

Fast Facts

  • Some research has found a link between levels of B12 and a higher risk of obesity or being overweight.
  • More research is needed to know whether taking B12 supplements can help people lose weight or maintain a healthy weight. 
  • Regardless of weight, if you’re not getting enough vitamin B12 in your diet, supplements can help. 

It doesn’t take much to put on a few pounds—a couple of extra beers here, a celebratory rib-eye there. But sometimes, extra weight can creep on even when you’re watching what you eat. If you’ve put on a few pounds and are really at a loss to explain why, it makes sense to ask your doctor about potential causes—including a vitamin B12 deficiency.

Not getting enough vitamin B12 can make you feel downright lousy. We’re talking dizzy, lethargic, depressed, and mentally foggy. And perhaps, a few pounds heavier. One 2020 review found that a vitamin B12 deficiency was linked to increased fat accumulation and obesity (1).

You might wonder if the inverse might be true: If a B12 deficiency is linked to weight gain, can supplementing with this essential nutrient help you drop pounds? Here’s what experts say.

What is Vitamin B12?

Vitamin B12, also known as cobalamin, is a water-soluble vitamin that your body need to operate at its peak. It helps your central nervous system function, is key to the  formation of red blood cells DNA, and—here’s where the weight connection comes in—is needed for energy metabolism (2), or how your body turns food into energy.

B12 Deficiency and Weight Gain

Some studies suggest that higher vitamin B12 levels may protect against obesity or being overweight. One study found that children and adolescents with higher vitamin B12 levels were less likely to be obese (3). An earlier study also showed that children with a higher body mass index (BMI) tend to have lower levels of vitamin B12 in their blood (4).

The link has been seen in adults, too. A 2019 study of over 9,000 adults found people with obesity had lower blood levels of vitamin B12. This was true even when researchers took into account other factors that can affect vitamin B12 levels, such as age, diet, lifestyle, and use of dietary supplements (5).

But these studies only show a link between vitamin B12 deficiencies and weight gain, says Matthew Cowling, D.O., a physical medicine and rehabilitation specialist in Madison, Wisconsin who specializes in weight loss. They don’t prove that having low B12 levels makes people gain weight—or that having higher B12 levels could help them slim down.  

Researchers are trying to tease out whether a cause and effect is happening. In one study, long-term use of vitamin B12 supplements was linked to lower levels of weight gain among middle-aged people over a 10-year period (6). But more research is needed to determine whether taking additional B12 might help people lose weight.

B12 and Weight

  • Your body needs vitamin B12 to help regulate energy metabolism, or how your body converts food into energy.
  • Some studies have linked low vitamin B12 levels to obesity, but research hasn’t proven that vitamin B12 deficiency causes weight gain.
  • Currently, researchers are trying to determine if B12 supplementation could help people control their weight.

Vitamin B12, now available from Hone, may boost your energy, help with weight, reduce stress, and support your brain. Connect with a doctor to see if it’s right for you. 

B12 Deficiency and Weight Gain

Although researchers are not certain why higher vitamin B12 levels are associated with a reduced risk of obesity or being overweight, they have a few theories.

Remember, vitamin B12 plays a critical role in energy metabolism (3). Cowling says without enough vitamin B12, the body can suffer from “metabolic distress,” which can show up as low energy levels, elevated triglyceride levels, anemia, problems with cognitive functioning, and insulin resistance. “Without B12, you can’t efficiently make energy and your metabolism suffers,” he says.

Some other ways that researchers think vitamin B12 deficiencies may be associated with weight gain:

  • The nutrient may influence how the body stores fat (7).
  • Since B12 is needed for protein synthesis to build muscle and repair tissues after physical activity, being short on the nutrient could prevent you from seeing gains from your workouts (8).
  • Without enough B12, your body may not make enough red blood cells, which shuttle oxygen to your muscles. This could leave you too fatigued to push hard at the gym—or to get there at all (9).

Can B12 Help With Energy and Endurance?

Weight aside, Cowling says higher doses of supplementation may increase energy and endurance in athletes. However, because vitamin B12 is water soluble, once the body has stored what it can in the tissues, excess amounts will be excreted in the urine (10). Cowling said the goal of using higher doses in athletes is to keep an optimum level of vitamin B12 in the tissues.

Research on the effect of vitamin B12 is limited. A couple of older studies found that supplementation did not improve exercise performance in adolescent males or healthy men without anemia (11). A more recent study showed that taking a pre-workout supplement containing vitamin B12 did not improve performance (12).

While supplementing with vitamin B12 may not improve performance in those who aren’t deficient, Cowling says that there is “legitimate use” of vitamin B12 supplementation if you’re deficient or even at risk of a deficiency (more on that below).


B12, Weight, and Energy

  • A vitamin B12 deficiency may increase the risk of fat storage, impair protein synthesis, and leave you too tired to exercise—all of which may lead you to gain weight.
  • If you’re deficient, supplementing with B12 can improve exercise performance, which can help keep your weight in check.
  • If you’re not deficient, getting more B12 may not have this effect. But taking B12 supplements may increase energy and endurance in athletes.

What Are Normal B12 Levels?

A normal vitamin B12 level in the blood is between 200 and 250 pc/mL. The cutoff varies by the type of test used and the laboratory processing the blood sample.

B12 Deficiency

The only way you’ll know whether your vitamin B12 levels are within the normal range is with a blood test. In addition to measuring the B12 levels in your blood, your doctor may also test your levels of methylmalonic acid (MMA), a substance that is formed when vitamin B12 is broken down in the body. If your MMA levels are high, it’s likely that you have a B12 deficiency.

He or she may also test your homocysteine levels. Homocysteine is an amino acid that is broken down by vitamin B12 to create other chemicals that your body needs. If your homocysteine levels are high, it can indicate a B12 deficiency.

You can ask your doctor about these tests if you’re experiencing symptoms of a vitamin B12 deficiency, or if you’re in an at-risk group.

What are the symptoms of B12 deficiency?

The symptoms of a vitamin B12 deficiency can be mild or severe. They may develop slowly, or rapidly (2).

  • Swollen and inflamed tongue
  • Fatigue
  • Fluttering or pounding heart
  • Pale skin
  • Weight loss
  • Numbness and tingling in the hands and feet
  • Depression
  • Infertility
  • Dementia

Considering B12 shots? Hone’s got you covered.


Who is at risk for a B12 deficiency?

People at risk of vitamin B12 deficiency include:

  • Older adults
  • People with diseases of the stomach or small intestine which impact your body’s ability to absorb nutrients, including celiac disease and Crohn’s disease
  • People who have had gastrointestinal surgery, such as bariatric surgery for weight loss
  • Vegans and vegetarians, since the biggest dietary sources of B12 are from animal products
  • People taking certain medications for long periods of time, such as proton pump inhibitors, histamine 2-receptor antagonists and metformin.

How to Get Enough B12

More research is needed before we will know whether vitamin B12 supplementation can support weight loss. But anyone who is at risk of vitamin B12 deficiency should make sure they are getting enough of the vitamin in their diet—or as supplements.

Adults should aim to get about 2.4 micrograms per day. Your body can’t make vitamin B12 so you need to get it from food or supplements, says Cowling.

Vitamin B12 is found naturally in B12-rich foods like fish, meat, poultry, eggs, and dairy products. In addition, it may be added to breakfast cereals, alternative milk beverages and other food products.

Vegans, vegetarians and others at risk of vitamin deficiency may need to take a multivitamin/mineral supplement containing vitamin B12 or a separate vitamin B12 supplement. These contain up to 1,000 micrograms or more of vitamin B12. This is higher than the daily Recommended Dietary Allowance (RDA) because your body does not absorb all of the B12 in the supplement.

If you have low vitamin B12 levels, your healthcare provider may recommend that you take B12 supplements or B12 injections to restore your blood levels of this vitamin.

You can also work with Hone to see if vitamin B12 injections are right for you. Simply create a Hone account, then fill out an online intake form. A board-certified physician will review your answers, and approve B12 shots if appropriate. If B12 injections are approved, they’ll be sent straight to your door.

The Bottom Line

Several studies have found a link between lower levels of vitamin B12 in the blood and a higher risk of obesity or being overweight. However, more research is needed to know if vitamin B12 supplements can support weight loss.