Symptoms of Vitamin B1 Overdose
Diet & NutritionNutrients & Supplements

Does a Vitamin B1 Overdose Cause Symptoms?

Does a Vitamin B1 Overdose Cause Symptoms?
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Updated on October 31, 2025
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Vitamin B1, or thiamine, supports normal cell function and helps your body convert food into energy. Thiamine overdose symptoms are unlikely to occur because this vitamin will be excreted in urine when consumed in excess. Vitamin B1 deficiency, on the other hand, can be a lot more harmful.

Thiamine overdose doesn't cause toxicity. In fact, there is no upper limit for this vitamin. Read on to learn more about how to safely add more vitamin B1 to your diet.

The Role of Vitamin B1

B-complex vitamins play a key role in energy production and metabolism. Some promote growth and development, while others support the formation of red blood cells, keep your brain sharp, or act as coenzymes in various biochemical reactions. Thiamine helps your body process the nutrients in food and use them for fuel. It regulates glucose metabolism and supports immune function.

The human body can store approximately 25 to 30 milligrams (mg) of thiamine, according to the National Institutes of Health Office of Dietary Supplements. About 80 percent of this is stored as thiamine diphosphate and helps your body metabolize fats, carbs, and amino acids.

Vitamin B1 also supports normal brain function. That's why low levels of this nutrient in the blood may lead to dementia, memory problems, apathy, fatigue, and behavioral changes, among other symptoms. Your brain needs thiamine to transmit nerve signals and function properly.

According to the Office of Dietary Supplements, the recommended daily intake of thiamine is 1.1 mg for women and 1.2 mg for men. Pregnant and nursing women should aim for about 1.4 mg per day.

Vitamin B1 Side Effects

Per the Office of Dietary Supplements, thiamine overdose is unlikely to cause side effects. If you consume too much of it, the excess will be eliminated in urine. There is no upper limit for vitamin B1, and doses of up to 50 mg appear to be safe.

Side effects of oral thiamine, according to the National Library of Medicine, could potentially include the following:

  • Flushing
  • Itching
  • Restlessness
  • Hives
  • Sweating
  • Weakness
  • Nausea

Other Sources of Vitamin B1

The symptoms of vitamin B1 deficiency are a lot more severe than those associated with a potential thiamine overdose. But luckily, thiamine deficiency is rare. Most foods contain varying doses of this vitamin. Whole grains, legumes, fish, seafood, and meat are just a few examples.

Fortified breakfast cereals, for instance, provide 100 percent of the daily value of thiamin, according to the Office of Dietary Supplements. If you're looking for low-carb options, fill up on tuna, steak, mussels, and yogurt. Beware that cooking and processing may reduce thiamine levels in food.

If you’re still interested in trying supplements, talk with your doctor before adding them to your daily intake.

Who Is at Risk for Vitamin B1 Deficiency?

According to the Office of Dietary Supplements, the following people are most at risk for thiamine deficiency:

  • Older adults
  • Those dependent on alcohol
  • People with HIV/AIDS
  • People with diabetes
  • Those who have had bariatric surgery
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Lynn Grieger, RDN, CDCES

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Lynn Grieger is a registered dietitian-nutritionist, certified diabetes care and education specialist, certified personal trainer, and certified health and wellness coach. She completed requirements to become a registered dietitian at Valparaiso University in 1987 and completed a dietetic internship at Ingalls Memorial Hospital in Harvey, Illinois, in 1988. 

Lynn brings her expertise in nutrition, exercise, and behavior change to her work in helping people reach their individual health and fitness goals. In addition to writing for Everyday Health, she has also written for websites and publications like Food and Health Communications, Today's Dietitian, iVillage.com, and Rodale Press. She has a passion for healthy, nutrient-dense, great-tasting food and for being outdoors as much as possible — she can often be found running or hiking, and has completed a marathon in every state.

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Andra Picincu, CN, CPT

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Andra Picincu is a certified nutritionist, personal trainer, and content writer with more than 15 years of experience. She holds bachelor’s degrees in psychology and in marketing and international business, and she’s dedicated to helping people improve their health through sustainable lifestyle changes.

She began her writing career when she was in college. Over the next few years, she took the steps to become a nutritionist and personal trainer, which allowed her to focus on these areas in her work. Today she contributes regularly to major health and lifestyle publications, including The List, Health Digest, Everyday Health, Aging in Place, and Stack. Her expertise revolves around sports nutrition, healthy eating, fitness, and mental well-being.

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