Vitamin B12 shots and supplements are popular among those looking for a quick fix for weight loss.

In fact, some even claim that increasing your intake of vitamin B12 can help fight fatigue, boost energy levels, and speed up your metabolism.

However, research on the potential effects of vitamin B12 on weight loss has turned up mixed results.

This article takes an in-depth look at the evidence to determine whether vitamin B12 can help promote weight loss.

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Also sometimes referred to as cobalamin, vitamin B12 is a water-soluble vitamin that’s essential for several aspects of health.

This vitamin is involved in forming DNA and red blood cells, as well as necessary for brain function, heart health, energy production, and more (1).

It’s found naturally in many animal products and sometimes added to fortified foods (1).

Vegans, vegetarians, older adults, and people with digestive issues that can interfere with nutrient absorption may be at a higher risk of vitamin B12 deficiency and need to supplement (2).


Vitamin B12 is a water-soluble vitamin involved in several aspects of health, including DNA synthesis, red blood cell formation, and brain function.

Although research in humans is still very limited, some studies suggest that vitamin B12 could affect body fat and metabolism.

One review concluded that vitamin B12 plays a key role in fat metabolism, noting that a deficiency could be linked to increased fat accumulation and obesity (3).

Another animal study found that severe vitamin B12 deficiency led to a significant increase in body fat percentage and cholesterol levels in pregnant mice (4).

What’s more, one animal study showed that administering B vitamins to rats fed a high fat diet reduced weight gain and increased levels of several enzymes that influence metabolism, compared with a control group (5).

However, current evidence is lacking, and additional high quality studies are needed to determine how vitamin B12 may affect metabolism and body fat in humans.


Some animal studies suggest that a deficiency in vitamin B12 may increase body fat percentage and alter metabolism. More research in humans is needed.

Interestingly, several studies have found that having adequate vitamin B12 levels may be associated with a lower risk of weight gain and obesity.

According to one large study in 9,075 people, having higher blood levels of vitamin B12 was associated with a lower risk of obesity (6).

Similarly, another study in 976 people showed that having low levels of vitamin B12 was linked to a higher risk of overweight or obesity (7).

What’s more, a study in 256 children showed that children with lower levels of vitamin B12 tended to have a higher body mass index (BMI), which is a measure of body size determined by height and weight (8).

However, keep in mind that while these studies show an association between vitamin B12 status and body weight, they don’t take other potentially contributing factors into account.

Therefore, it can’t be concluded that vitamin B12 causes weight loss. More research is needed to determine whether vitamin B12 directly affects body weight or BMI.


Some studies show that lower levels of vitamin B12 may be associated with a higher risk of overweight or obesity. Further studies are needed to determine whether other factors may also be involved.

A vitamin B12 deficiency can lead to megaloblastic anemia, a condition characterized by a low number of red blood cells that are larger than normal (9).

Megaloblastic anemia can cause a variety of symptoms and side effects, including (10):

  • shortness of breath
  • headache
  • heart palpitations
  • fatigue
  • poor balance
  • memory loss

That said, being low in vitamin B12 doesn’t always lead to megaloblastic anemia, and many people may only experience mild symptoms like fatigue (11).

Furthermore, while a deficiency in vitamin B12 may not cause weight gain, it can decrease energy levels and contribute to fatigue, making it harder to stay active and manage your weight.

Conversely, some studies show that a deficiency in vitamin B12 may cause appetite loss, potentially leading to weight loss if left untreated (12, 13).

If you’re low or deficient in B12, your healthcare provider will likely recommend oral vitamin B12 supplements or injections to increase your blood levels (10).


Low levels of vitamin B12 can cause megaloblastic anemia, which is characterized by shortness of breath, headaches, and fatigue. Increasing your vitamin B12 intake can protect against deficiency to prevent these side effects.

Vitamin B12 is found naturally in various food sources, including animal products like meat, fish, poultry, eggs, milk, and milk products (1).

It’s also added to many fortified foods, such as breakfast cereals and plant-based milk like almond, soy, or hemp milk (1).

Vitamin B12 supplements are also available in several forms, including tablets, capsules, liquids, and lozenges.

It’s often found in many multivitamin supplements as well.

Those who don’t regularly consume animal products rich in vitamin B12 may want to consider adding fortified foods to their diet or taking a supplement to ensure that their nutritional needs are met.


Vitamin B12 is found in animal products and fortified foods. It’s also available in supplement form to help you meet your needs.

Vitamin B12 is an important water-soluble vitamin that plays a central role in several aspects of health, including brain function, heart health, and the production of red blood cells and DNA.

Studies show that having adequate blood levels of vitamin B12 may be linked to a lower risk of obesity in children and adults. Plus, animal research suggests that vitamin B12 may affect body fat and metabolism.

Increasing your intake of vitamin B12 through foods or supplements can help prevent deficiency, which may improve side effects like low energy levels and fatigue.

However, if you’re already getting enough vitamin B12 in your diet and don’t have a nutrient deficiency, it’s unclear whether increasing your intake of vitamin B12 will have much of an effect on weight loss.