Thiamin (Vitamin B1): What It Does, Who Runs Low, and the Foods That Cover Your Day
Thiamin (Vitamin B1): What It Does, Who Runs Low, and the Foods That Cover Your Day
In a lot of hospitals there is a rule that sounds backwards. When certain people come in weak, confused, or unable to keep food down, staff give them a vitamin before they give them sugar. That vitamin is thiamin, vitamin B1.
Most people never need to think about thiamin, because most people get plenty from food. But for the people who run low, it matters a great deal. If you have searched "what does thiamin do" or "foods high in thiamin," here is what the research says.
What does thiamin do
Thiamin is one of the water-soluble B vitamins. Your body turns it into an active form (thiamin diphosphate) that works as a helper for five enzymes involved in breaking down carbohydrate, protein, and fat.
The best-known job is with carbohydrate. After you eat bread, rice, fruit, or pasta, your cells break it down into glucose. To burn that glucose for real energy, the cell has to move it through a gate called pyruvate dehydrogenase, and that gate needs thiamin. Without enough, the fuel backs up before it can be burned and the cell runs short on energy. The brain, nerves, and heart feel it first.
That is also why the hospital rule exists. In someone whose thiamin is already low, a big load of sugar uses up what is left. European neurology guidelines say thiamin should be given before any carbohydrate in suspected deficiency (Galvin 2010, PMID 20642790).
How much thiamin do you need a day
| Group | Daily need |
|---|---|
| Men 19 and older | 1.2 mg |
| Women 19 and older | 1.1 mg |
| Pregnancy or breastfeeding | 1.4 mg |
The Daily Value on food labels is 1.2 mg. There is no upper limit, because no harm has been reported at intakes of 50 mg a day or more, and absorption drops off sharply above about 5 mg.
The adult body holds only about 25 to 30 mg of thiamin in total, mostly in the liver, and it turns over quickly. You need a steady supply from food.
Most Americans get it. Average intake from food is about 1.95 mg a day for men and 1.39 mg for women, and only about 6 percent of people fall below the average requirement.
Who is at risk of thiamin deficiency
Long-term heavy drinking. The most common cause in wealthy countries. Up to 80 percent of people with chronic alcohol use disorder develop thiamin deficiency, because alcohol lowers absorption, drains liver stores, and blocks thiamin's activation, and diets often suffer too.
Older adults. Up to 20 to 30 percent show lab signs of some deficiency, from smaller appetites, more medications, chronic illness, and lower absorption. Risk is higher in care facilities.
Heart failure and loop diuretics. Poor thiamin status has been reported in 21 to 98 percent of heart failure patients across studies. In one, 33 percent of 100 heart failure patients were deficient, compared with 12 percent of 50 healthy volunteers (Hanninen 2006, PMID 16412860). Furosemide increases thiamin loss in urine.
Eating much less than usual. Enriched grains supply about half of the thiamin Americans eat (Fulgoni 2011, PMID 21865568). When appetite drops and grains fall off the plate, intake can drop with them.
After weight-loss surgery. A systematic review found 84 published cases of Wernicke's encephalopathy after bariatric surgery. 94 percent appeared within six months of surgery, frequent vomiting was a factor in 90 percent, and about half did not fully recover (Aasheim 2008, PMID 18948797). Guidelines recommend checking thiamin for at least six months after surgery. Your surgical team manages this.
Diabetes. Several small studies have found lower thiamin status in people with diabetes. What that means for long-term health is not yet known.
Thiamin deficiency symptoms
Early signs can include poor appetite and weight loss, confusion, short-term memory problems, muscle weakness, and heart symptoms.
Beriberi mainly affects the nerves, with numbness, weak reflexes, and muscle wasting, and rarely heart failure with leg swelling. It is rare in the United States and responds quickly to treatment.
Wernicke-Korsakoff syndrome is the more common form in the US, about 8 to 10 times more common with chronic alcohol use. Wernicke's encephalopathy is the acute stage, and up to 20 percent of untreated people die. Korsakoff syndrome is the chronic stage, with severe memory loss and confusion, and about a quarter of people do not recover even with treatment.
Treatment doses are set by clinicians, often by IV. Do not try to self-treat a suspected deficiency.
Do athletes need more vitamin B1
Probably not more than food already gives them. A review of B vitamins and exercise found that active people with poor or marginal B vitamin status may perform worse at high intensity, and that athletes who restrict energy or cut food groups are the ones at risk. The review named riboflavin and vitamin B6 as the B vitamins exercise may raise needs for. Thiamin was not on that list (Woolf and Manore 2006, PMID 17240780).
Athletes who eat enough usually get extra thiamin automatically, because the foods that carry the carbs (enriched pasta, rice, bread, beans) carry the B1 too. The gaps show up with under-eating, cutting out grains, or fueling mainly on sugar from gels and sports drinks.
Do you need a thiamin supplement
For most people, no. Multivitamins usually carry about 1.5 mg. Thiamin is very safe, but safe is not the same as needed. Benfotiamine, a synthetic fat-soluble form, is sold for diabetic nerve pain, with a few small trials showing mixed results. If you are in one of the risk groups above, talk with your doctor or dietitian about testing and dosing.
Best food sources of thiamin
| Food | Serving | Thiamin (mg) | % Daily Value |
|---|---|---|---|
| Fortified breakfast cereal | 1 serving | 1.2 | 100 |
| Egg noodles, enriched | 1 cup cooked | 0.5 | 42 |
| Pork chop | 3 oz | 0.4 | 33 |
| Trout | 3 oz | 0.4 | 33 |
| Black beans | 1/2 cup | 0.4 | 33 |
| English muffin, enriched | 1 | 0.3 | 25 |
| Mussels | 3 oz | 0.3 | 25 |
| Brown rice | 1/2 cup | 0.2 | 17 |
| Acorn squash | 1/2 cup | 0.2 | 17 |
| White rice, enriched | 1/2 cup | 0.1 | 8 |
| Whole wheat bread | 1 slice | 0.1 | 8 |
Source: NIH Office of Dietary Supplements, USDA FoodData Central. Chicken, cheese, and most fruit carry little to none.
Two cooking notes. Unenriched white rice has about one-tenth the thiamin of brown rice. And thiamin dissolves in water, so draining cooking water loses some. Rice cooked until the water is absorbed, soups, and stews hold onto it.
Putting it on a plate
Our Issue 017 recipe is cumin pork with black beans, brown rice, and roasted acorn squash. Pork, black beans, and brown rice together bring about 1 mg of thiamin per plate, most of the day. The rice is cooked until the water is gone and never drained, so the B1 stays in the pot. No pork? Trout carries the same thiamin per serving.
The short version
- Thiamin (vitamin B1) helps your cells turn carbohydrate into energy.
- Adults need 1.1 to 1.2 mg a day, and most Americans get more than that from food.
- The body holds only about 25 to 30 mg, so you need a steady supply.
- The people at real risk: long-term heavy drinkers, older adults, people with heart failure on water pills, people eating far less than usual, and people after weight-loss surgery.
- Confusion and unsteadiness in someone at risk is an emergency.
- Pork, beans, trout, and enriched or whole grains are the best everyday sources.
About the evidence
This article is the evergreen companion to The Vitamin Letters, Issue 017, and draws on Anchor & Apex's curated micronutrient science (Stephanie Clarke) with fresh citation pulls by Giada. Intake targets, intake data, risk-group figures, deficiency descriptions, and food values come from the NIH Office of Dietary Supplements thiamin fact sheet (updated 2023), built on the Institute of Medicine Dietary Reference Intakes and USDA FoodData Central. Additional sources: the EFNS Wernicke guideline (Galvin 2010, PMID 20642790), a systematic review of Wernicke's after bariatric surgery (Aasheim 2008, PMID 18948797), heart failure prevalence (Hanninen 2006, PMID 16412860), US nutrient sources (Fulgoni 2011, PMID 21865568), and B vitamins in exercise (Woolf and Manore 2006, PMID 17240780). This is general education, not individualized medical or nutrition advice. Supplement decisions belong with your own clinician.
Work with Shawn. Shawn is a registered dietitian who helps people stop fighting food, whether you are leaving food rules behind, chasing a health goal, or fueling hard training. See how he works at anchorandapex.com/anchor.
Next in the series: vitamin B6, the B vitamin where too much can hurt.
This article is for educational purposes and does not constitute medical advice. If this is relevant to you, please work with your physician and a registered dietitian on an individualized approach.
Be gentle with yourself out there. You are doing better than you think. ♡
Maggie Cooper
Written by Maggie Cooper · Blog & Website Copywriter · Anchor & Apex
"Smart science, soft landing. Honest words that leave you a little wiser and a lot kinder to yourself."