Should I take B12 if I have hypothyroidism?: Understanding the Connection

October 31, 2025 •

4 min read

Recent research shows a strong connection between hypothyroidism and vitamin B12 deficiency, with some studies indicating a prevalence as high as 40% in patients. So, should I take B12 if I have hypothyroidism? The answer often depends on your individual health status, which is why a thorough understanding of the relationship between these two conditions is essential.

Quick Summary

This article explores the significant link between hypothyroidism and vitamin B12 deficiency, explaining how impaired absorption and autoimmune factors increase the risk. It details the overlapping symptoms, the importance of accurate testing, and discusses dietary sources versus supplements for managing low B12 levels.

Key Points

High Prevalence: Studies show a high rate of B12 deficiency in hypothyroid and Hashimoto's patients, sometimes as high as 40%.
Symptom Overlap: Many symptoms, such as fatigue, depression, and neurological issues, are common to both hypothyroidism and B12 deficiency, making diagnosis complex.
Malabsorption Risk: Hypothyroidism, especially the autoimmune form (Hashimoto's), increases the risk of pernicious anemia, which impairs B12 absorption.
Test First, Then Treat: Never self-prescribe B12. Get a blood test to confirm a deficiency before starting supplementation, as symptoms alone are not a reliable indicator.
Supplementation Options: Depending on the severity and cause, supplementation can be in the form of oral pills, sublingual lozenges, or intramuscular injections.
Dietary Support: While diet alone may not correct a deficiency, consuming B12-rich foods like meat, fish, and dairy is a crucial part of a balanced nutritional strategy.

The Overlapping Symptoms of B12 Deficiency and Hypothyroidism

Many of the symptoms of vitamin B12 deficiency can mimic or worsen those already experienced with hypothyroidism. Both conditions can cause profound fatigue, weakness, and mood disturbances like depression. This overlap can make it difficult to determine the root cause of certain symptoms without proper testing. In addition to fatigue, both can also lead to neurological issues, including numbness, tingling, and memory problems. For individuals already managing an underactive thyroid, a coexisting B12 deficiency can intensify these issues and significantly impact overall quality of life.

The Mechanisms Behind Impaired B12 Absorption

There are several reasons why individuals with hypothyroidism are at a higher risk of developing a vitamin B12 deficiency. One of the most significant links is the common co-occurrence of autoimmune conditions. Many cases of hypothyroidism are caused by Hashimoto's thyroiditis, an autoimmune disease. Autoimmune diseases often increase the risk for other autoimmune disorders, including pernicious anemia, which prevents the absorption of vitamin B12 in the stomach.

In pernicious anemia, the body's immune system attacks the parietal cells in the stomach, which are responsible for producing intrinsic factor. Intrinsic factor is a protein essential for the absorption of B12 in the small intestine. Without it, dietary and supplemental B12 cannot be properly assimilated. Even in the absence of pernicious anemia, a slowed metabolism and gut motility, common in hypothyroidism, can contribute to poor nutrient absorption.

Is B12 Supplementation Necessary?

Whether or not you need to take a B12 supplement should always be determined by a healthcare provider based on a blood test. It is not recommended to start supplementation without a diagnosed deficiency. If a deficiency is confirmed, supplementation can significantly improve related symptoms like fatigue and neuropathy. The form of supplementation—oral pills, sublingual lozenges, or injections—depends on the severity of the deficiency and the underlying cause. For example, if malabsorption is the primary issue due to pernicious anemia, injections may be more effective than oral supplements.

Oral Supplements: High-dose oral supplementation is one method that may be effective for many individuals.
Intramuscular Injections: For those with severe malabsorption, injections are often required and typically involve a schedule determined by a healthcare provider.
Sublingual B12: Sublingual (under the tongue) forms can also be an effective alternative to injections, as they bypass the digestive system for absorption.

Dietary Sources vs. Supplements

For those with hypothyroidism, maintaining adequate B12 levels through diet is a good preventive strategy, but it may not be enough to correct an existing deficiency. Since B12 is predominantly found in animal products, those following a vegetarian or vegan diet are at higher risk of deficiency and may need to rely on fortified foods or supplements.

Excellent Dietary Sources of B12:

Meat (especially liver)
Poultry
Fish (salmon, tuna)
Eggs
Dairy products (milk, cheese, yogurt)
Fortified breakfast cereals

Comparison of B12 Delivery Methods


Feature	Dietary Intake	Oral Supplements	Sublingual Lozenges	Intramuscular Injections
Effectiveness	May be insufficient for those with absorption issues.	Can be effective for some individuals, often requiring high concentrations.	Very effective, as it bypasses the digestive system.	Highly effective for severe deficiencies or malabsorption.
Absorption Pathway	Relies on intrinsic factor in the stomach.	Relies on a functioning digestive system, though high concentrations can allow passive absorption.	Absorbed directly into the bloodstream through the mucous membranes.	Absorbed directly into the bloodstream via muscle tissue.
Convenience	Requires consistent intake of animal-based or fortified foods.	Easy to take.	Convenient, dissolves in the mouth.	Requires administration by a healthcare provider.
Cost	Part of a regular food budget.	Relatively inexpensive.	Moderate cost.	Can be more expensive due to clinical administration.

Screening and Monitoring

Given the high prevalence of B12 deficiency among hypothyroid patients, many endocrinologists recommend routine screening for vitamin B12 levels. This is particularly important for those with autoimmune hypothyroidism (Hashimoto's) and those who continue to experience symptoms like fatigue, numbness, and memory issues despite adequate thyroid hormone replacement therapy. Standard B12 blood tests can sometimes be misleading, so some doctors may also look at other markers like methylmalonic acid (MMA) to get a more accurate picture of B12 status. Early detection and treatment of B12 deficiency are crucial to prevent long-term neurological complications.

A Holistic Approach to Managing Hypothyroidism

Managing hypothyroidism and any coexisting B12 deficiency requires a comprehensive strategy that goes beyond medication alone. A nutrient-dense diet, rich in B12 and other essential vitamins and minerals, is a foundational element. Addressing any underlying autoimmune issues is also key. Regular follow-ups with a healthcare provider are necessary to monitor both thyroid hormone levels and B12 status to ensure optimal health outcomes. For further reading on managing thyroid health through diet and lifestyle, the British Thyroid Foundation offers valuable resources on their website.

Conclusion

For many individuals, the answer to "should I take B12 if I have hypothyroidism?" is yes, but only after proper diagnosis. The strong association between these two conditions, driven by autoimmune factors and malabsorption, makes B12 deficiency a common concern for hypothyroid patients. Because the symptoms of both can overlap, it's vital to get tested to determine if a deficiency exists. When a deficiency is confirmed, supplementation is a highly effective way to alleviate symptoms and improve overall well-being. A collaborative approach involving your doctor, regular testing, and a thoughtful nutritional plan will ensure you manage both conditions effectively.

Frequently Asked Questions

Yes, hypothyroidism, especially the autoimmune form known as Hashimoto's thyroiditis, can lead to conditions like atrophic gastritis and pernicious anemia, which impair the body's ability to absorb vitamin B12 from food and supplements.

Both conditions can cause overlapping symptoms such as profound fatigue, memory problems, depression, muscle weakness, and numbness or tingling in the hands and feet.

The most common way is a blood test to measure serum vitamin B12 levels. In some cases, a doctor might also order a methylmalonic acid (MMA) test for a more accurate assessment, especially if the initial B12 result is borderline.

High-concentration oral supplementation can be effective even with some malabsorption, as it allows for passive absorption. However, for severe malabsorption, your doctor may recommend injections.

No, B12 supplements do not negatively interact with thyroid medication like levothyroxine. In fact, improving B12 status can help alleviate symptoms that may persist despite optimal thyroid hormone levels.

The best method depends on the individual. Injections are most effective for severe deficiencies or diagnosed pernicious anemia. For mild to moderate deficiencies, oral or sublingual supplements can be effective.

Vitamin B12 is naturally found in animal products. Good sources include meat (especially organ meats), fish, poultry, eggs, milk, cheese, and fortified foods like breakfast cereals.