Thiamin (Vitamin B1): What It Does and Why You Need It

A basic look at the vitamin that helps your body turn food into usable energy.

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By the Ration Editorial Team · Reviewed against primary research · Updated July 14, 2026

Thiamin, also known as vitamin B1, is a water soluble vitamin. That means your body cannot store much of it, so you need a steady supply from food.

It was one of the first vitamins ever discovered. Researchers identified it while studying beriberi, a disease caused by thiamin deficiency that affects the nerves and heart.

Today, thiamin is added to many refined grain products specifically because deficiency used to be a widespread public health problem.

Thiamin acts as a coenzyme, meaning it helps other enzymes do their jobs. Its main role is in energy metabolism, helping convert carbohydrates and some amino acids into usable fuel for cells.

It is especially important for cells that rely heavily on glucose for energy, including neurons. This is why thiamin deficiency shows up as nerve and brain symptoms before much else.

Thiamin also supports the synthesis of certain neurotransmitters and plays a role in maintaining the protective sheath around nerve fibers.

Severe thiamin deficiency causes beriberi, which comes in two main forms.

• Wet beriberi, which affects the cardiovascular system and can cause an enlarged heart, rapid heart rate, and fluid buildup
• Dry beriberi, which affects the nervous system and can cause numbness, muscle weakness, and difficulty walking
• Wernicke-Korsakoff syndrome, a serious brain disorder linked to chronic alcohol use disorder that involves confusion, poor coordination, and memory problems

In wealthy countries, outright beriberi is uncommon. People at higher risk of low thiamin status include those with alcohol use disorder, people who have had bariatric surgery, people with poorly controlled diabetes, and those with very restrictive diets or prolonged vomiting.

Thiamin is found in a wide range of whole and fortified foods. Pork, legumes, seeds, and whole grains are among the richest natural sources, and many breakfast cereals and refined grain products are fortified specifically to prevent deficiency.

Because thiamin is water soluble and sensitive to heat, prolonged cooking in water can reduce the amount retained in food. Steaming or quick cooking methods generally preserve more of it than long boiling.

Recommended intakes are generally set around 1.1 to 1.2 milligrams per day for most adults, with somewhat higher needs during pregnancy and breastfeeding.

Most people eating a varied diet that includes whole grains, legumes, or fortified cereals meet this easily. Supplemental thiamin is typically only considered relevant for people with documented deficiency risk, and any decisions about supplements are best made with a healthcare provider rather than on your own.

Thiamin has a strong safety profile. Because it is water soluble, excess amounts are generally excreted in urine rather than building up to toxic levels.

No tolerable upper intake level has been established for thiamin, reflecting the low risk of toxicity from oral intake. Reported side effects from high doses are rare and usually mild, such as stomach upset.

People with alcohol use disorder, malabsorption conditions, or those on dialysis may have different thiamin needs and should discuss this with a clinician rather than self-treating.

• People with alcohol use disorder or a history of heavy alcohol use
• People who have had bariatric or weight loss surgery
• People with poorly controlled diabetes or on certain diuretics
• People with very restrictive diets, prolonged vomiting, or malabsorption conditions
• Older adults with poor overall nutrition

Thiamin is a foundational nutrient for turning food into energy and keeping nerves functioning normally. Deficiency is uncommon in places with fortified grain supplies, but certain groups, particularly people with alcohol use disorder, remain at meaningful risk.

For most people, eating a varied diet with whole grains, legumes, seeds, and some pork covers thiamin needs without any need for supplements.