What Vitamin Deficiency Causes Fish Odor Syndrome? Unpacking TMAU's Triggers

November 16, 2025 •

4 min read

Trimethylaminuria (TMAU), also known as fish odor syndrome, is a rare metabolic disorder primarily caused by an inherited genetic defect, though a vitamin B2 deficiency can be a factor in some acquired cases. This unpleasant body odor is not a result of poor hygiene but rather an internal metabolic issue that prevents the body from properly processing a specific chemical.

Quick Summary

Trimethylaminuria (TMAU), or fish odor syndrome, is most often a genetic disorder affecting the FMO3 enzyme. An acquired form can be linked to factors like vitamin B2 deficiency, with dietary changes and riboflavin supplements often helping manage symptoms.

Key Points

Genetic Defect: The primary cause of fish odor syndrome (TMAU) is an inherited mutation in the FMO3 gene, which prevents the proper breakdown of trimethylamine (TMA).
Vitamin B2 Role: A deficiency in vitamin B2 (riboflavin) is not the main cause but can contribute to acquired TMAU, as riboflavin is a cofactor for the FMO3 enzyme.
Dietary Triggers: Foods rich in choline and L-carnitine, such as eggs, fish, liver, and some legumes, are broken down by gut bacteria to produce TMA, exacerbating symptoms.
Management Strategies: Treatment involves a low-choline diet, supplementation with riboflavin, activated charcoal, or copper chlorophyllin, and using low pH soaps.
Genetic vs. Acquired: Primary TMAU is inherited, while secondary or acquired TMAU can result from diet, medication, liver/kidney disease, or gut imbalance.
Symptom Reduction: Managing stress and using pH-balanced personal hygiene products can help reduce the unpleasant odor in sweat and other bodily fluids.

The Primary Cause: A Genetic Defect

The most common cause of fish odor syndrome is a genetic condition known as primary trimethylaminuria (TMAU). This is an autosomal recessive disorder caused by a mutation in the flavin-containing monooxygenase 3 (FMO3) gene. In healthy individuals, the FMO3 enzyme, primarily located in the liver, is responsible for converting a foul-smelling chemical called trimethylamine (TMA) into the odorless compound trimethylamine N-oxide (TMAO).

When a person has primary TMAU, their FMO3 enzyme is either nonfunctional or entirely absent due to the genetic mutation. This enzyme deficiency prevents the proper breakdown of TMA, leading to an accumulation of the chemical in the body. This excess TMA is then excreted through bodily fluids, including sweat, urine, breath, and vaginal secretions, producing the characteristic fishy odor.

The Role of Vitamin B2 (Riboflavin) Deficiency

While the primary cause is genetic, a deficiency in vitamin B2 (riboflavin) has been identified as a contributing factor in some acquired, or secondary, cases of TMAU. Riboflavin is a necessary cofactor for the FMO3 enzyme to function effectively. For some individuals with residual FMO3 enzyme activity, ensuring adequate riboflavin levels can enhance the enzyme's function and improve their condition.

In these cases, supplementing with riboflavin (vitamin B2) has been shown to reduce the amount of TMA excreted and alleviate the odor. It is important to note that this treatment is not a cure for the underlying genetic disorder but rather a management strategy to support the remaining enzyme activity. A healthcare provider can determine if riboflavin supplementation is appropriate.

Diet and Other Contributing Factors

Diet plays a significant role in managing TMAU, as the condition is triggered by specific chemical compounds found in food. Gut bacteria produce TMA from dietary precursors, which must then be metabolized by the FMO3 enzyme.

Here are the primary dietary precursors and other exacerbating factors:

Choline: Found in eggs, liver, legumes (peas, soybeans), and certain types of fish. High dietary intake can increase TMA production. Choline supplements can also trigger symptoms.
L-Carnitine: Present in red meat and fish. This supplement is also sometimes used by athletes, which can lead to acquired TMAU symptoms.
Gut Microbiome Imbalance: An overgrowth of TMA-producing bacteria can overwhelm even a partially functioning FMO3 enzyme.
Liver or Kidney Disease: Severe dysfunction of these organs can impair the body's ability to process TMA.
Hormonal Fluctuations: Stress, menstruation, and other hormonal changes can sometimes worsen the symptoms.

Management Strategies for Fish Odor Syndrome

Managing TMAU symptoms often requires a multi-pronged approach that includes dietary adjustments, supplementation, and other lifestyle changes. It is important to work with a medical professional, such as a genetic counselor or dietitian, to create an effective plan.

Here are some common management strategies:

Low-Choline Diet: Limiting or avoiding high-choline foods, such as eggs, offal, and certain legumes, can significantly reduce TMA production.
Riboflavin (Vitamin B2) Supplementation: In some cases, especially where some FMO3 activity exists, high-dose riboflavin supplements can enhance enzyme function and reduce odor.
Specific Supplements: Activated charcoal or copper chlorophyllin supplements can help bind and neutralize TMA in the gut before it's absorbed.
Antibiotics: Short courses of antibiotics can suppress the TMA-producing gut bacteria in severe cases, but this should be done under a doctor's supervision.
Hygiene Practices: Using slightly acidic soaps and lotions with a pH of 5.5–6.5 can help remove TMA from the skin's surface. Avoiding excessive sweating and managing stress can also help.

Comparing Primary vs. Secondary Trimethylaminuria


Feature	Primary (Genetic) TMAU	Secondary (Acquired) TMAU
Cause	Inherited mutation in the FMO3 gene.	Caused by dietary overload, gut microbiome imbalance, liver/kidney disease, or other factors.
FMO3 Enzyme Function	Severely deficient or non-functional.	Overwhelmed by excessive TMA production or compromised function due to other health issues.
Onset	Can appear in infancy or childhood.	Typically starts in adulthood or is transient, appearing during periods like menstruation.
Inheritance	Autosomal recessive pattern (inheriting two mutated genes).	Not inherited; depends on other health or dietary factors.
Response to Riboflavin	Can be effective in cases with some residual enzyme function.	Can be effective if deficiency is a contributing factor.

Conclusion

While the search query specifically asks what vitamin deficiency causes fish odor syndrome, the reality is more complex. The condition, known as trimethylaminuria (TMAU), is most commonly a genetic disorder caused by a faulty FMO3 gene. A vitamin B2 (riboflavin) deficiency is not the root cause of the primary genetic form but can be a factor in acquired cases. Fortunately, management strategies involving dietary modifications, riboflavin supplementation, and other therapies can significantly reduce symptoms and improve the quality of life for those affected.

For more comprehensive information on the genetic underpinnings of Trimethylaminuria, please refer to the resource available on the NCBI Bookshelf.

Frequently Asked Questions (FAQs)

Frequently Asked Questions

The primary cause of fish odor syndrome, or Trimethylaminuria (TMAU), is an inherited genetic defect in the FMO3 gene. This gene produces an enzyme that normally breaks down the smelly compound trimethylamine (TMA).

A vitamin deficiency does not cause the genetic form of TMAU. However, a vitamin B2 (riboflavin) deficiency can be a contributing factor in acquired or secondary cases of TMAU. Riboflavin is essential for the FMO3 enzyme's function.

Yes, for some individuals with residual FMO3 enzyme activity, taking riboflavin (vitamin B2) supplements can enhance the enzyme's function and help reduce the odor. This is often part of a broader management strategy.

Individuals with TMAU should limit or avoid foods high in choline and carnitine. These include eggs, liver, certain beans and legumes, some types of seafood, and red meat.

Currently, there is no cure for primary (genetic) TMAU. However, the condition can be effectively managed through a combination of dietary changes, supplements like activated charcoal and riboflavin, and specialized hygiene practices.

TMAU is typically diagnosed through a specialized urine test that measures the ratio of trimethylamine (TMA) to its odorless metabolite, trimethylamine N-oxide (TMAO). Genetic testing for FMO3 mutations may also be performed.

Yes, stress and other emotional factors can exacerbate the symptoms of fish odor syndrome. Stress can increase sweating, which in turn can increase the release of trimethylamine through the skin.