Can Low B12 Make You Sleepy All the Time?

December 7, 2025 •

3 min read

According to the Mayo Clinic, fatigue and weakness are common symptoms for those with low B12 levels, a deficiency that affects millions. So, can low B12 make you sleepy all the time? A deficiency can significantly impact your energy levels by hindering red blood cell production, leading to persistent tiredness.

Quick Summary

A vitamin B12 deficiency can severely impact energy levels by causing anemia and affecting neurological function, leading to chronic fatigue. Treatment options include dietary changes, supplements, or injections. It's crucial to address the root cause, as symptoms can mimic other health issues, necessitating a proper diagnosis.

Key Points

Fatigue Link: Low B12 often leads to chronic fatigue because it is essential for producing energy and healthy red blood cells.
Anemia Cause: A severe B12 deficiency can cause megaloblastic anemia, which impairs oxygen transport and results in persistent weakness.
Nerve Damage: B12 is crucial for nerve health; a deficiency can cause nerve damage that contributes to fatigue and weakness.
High-Risk Groups: Vegans, older adults, and those with specific digestive disorders are particularly susceptible to B12 deficiency.
Treatment Options: Treatments range from oral supplements for mild cases to injections for severe deficiencies and malabsorption issues.
Consult a Doctor: Persistent fatigue warrants a medical evaluation to determine if a B12 deficiency or another underlying cause is responsible.

The Connection Between Low B12 and Constant Fatigue

Vitamin B12, or cobalamin, is a vital nutrient for several key bodily functions, including red blood cell formation, DNA synthesis, and maintaining a healthy nervous system. When levels are too low, the body's processes are disrupted, and one of the most prominent symptoms is persistent tiredness.

How Low B12 Causes Fatigue

Megaloblastic Anemia: A severe B12 deficiency can cause megaloblastic anemia, a condition characterized by abnormally large, immature red blood cells that cannot effectively carry oxygen. This reduced oxygen delivery to tissues leads to chronic fatigue and weakness.
Neurological Impact: B12 is crucial for nerve health. A deficiency can damage the protective myelin sheath, leading to neurological symptoms like numbness, tingling, difficulty with balance, and contributing to feelings of weakness. It can also affect brain function, causing difficulty concentrating and mood changes.

Who Is at Risk for Low B12?

Certain groups have a higher risk of developing a B12 deficiency, including:

Vegans and Vegetarians: B12 is primarily found in animal products, requiring those on plant-based diets to use fortified foods or supplements.
Older Adults: The ability to absorb B12 from food often decreases with age.
Individuals with Digestive Disorders: Conditions like Crohn's disease, celiac disease, and atrophic gastritis impair B12 absorption.
People with Pernicious Anemia: An autoimmune condition affecting the absorption of B12.
Patients on Certain Medications: Some medications, like proton pump inhibitors and metformin, can interfere with B12 absorption.

Diagnosing and Treating B12 Deficiency

A healthcare professional can diagnose a B12 deficiency with blood tests. Treatment depends on the severity and cause, aiming to restore B12 levels and alleviate symptoms.

Comparison of B12 Treatment Options


Treatment Method	Best For	How It Works	Benefits	Drawbacks
Dietary Changes	Mild deficiency, preventative care	Consuming B12-rich foods or fortified products.	Natural, long-term, no side effects.	Slow results, only for dietary causes.
Oral Supplements	Mild to moderate deficiency	Taking high-dose B12 tablets.	Convenient, non-invasive, cost-effective.	Absorption can be poor in those with malabsorption.
B12 Injections	Severe deficiency, pernicious anemia, malabsorption issues	Intramuscular injections.	Rapidly increases levels, bypasses digestive issues.	Requires medical supervision, can be inconvenient.

Beyond B12: Other Causes of Persistent Sleepiness

Fatigue can stem from various factors even with normal B12 levels. Other potential causes include:

Sleep Disorders: Conditions like sleep apnea and insomnia disrupt rest.
Iron Deficiency Anemia: Another form of anemia causing fatigue.
Thyroid Problems: Both hyper- and hypothyroidism affect energy.
Mental Health Issues: Stress, depression, and anxiety impact energy levels.
Lifestyle Factors: Diet, hydration, and activity levels play a role.

Conclusion: Getting to the Root of the Problem

Low B12 can indeed cause persistent sleepiness by affecting red blood cell production and the nervous system, leading to significant fatigue. Individuals in high-risk groups should consider screening for B12 deficiency if experiencing unexplained tiredness. However, since fatigue can indicate various health issues, a doctor's evaluation is crucial to determine the exact cause and ensure proper treatment. For more detailed information on diagnosis and management of B12 deficiency, consult the American Academy of Family Physicians' resource, {Link: AAFP aafp.org}.

Frequently Asked Questions

Recovery time varies depending on the severity of the deficiency and the treatment method. With proper treatment, such as injections for severe cases, many people begin to see improvement within a few weeks to months.

Naturally, B12 is found almost exclusively in animal products. Vegans and vegetarians can get B12 from fortified foods like certain cereals, nutritional yeast, and plant-based milks, or by taking supplements.

The first signs often include fatigue and weakness. Other early symptoms can be pale skin, a sore tongue, or tingling sensations in the hands and feet.

For individuals with normal B12 levels, there is no evidence that extra supplementation will provide an energy boost. Supplements are most effective for those with a confirmed deficiency.

Injections deliver B12 directly into the muscle, bypassing the digestive system, which is ideal for those with severe deficiencies or malabsorption issues. Oral supplements are convenient but rely on adequate digestive absorption.

Conditions such as pernicious anemia, celiac disease, Crohn's disease, and atrophic gastritis can all interfere with the body's ability to absorb vitamin B12.

Yes, a B12 deficiency can impact the nervous system and is associated with psychological symptoms like depression, anxiety, memory issues, and confusion.