Vitamin B1 (as thiamine mononitrate)

What is vitamin B1?

Vitamin B1, or thiamine, is a water-soluble B vitamin. The body uses it as a helper molecule for enzymes that break down glucose and other carbohydrates to release energy, and it is especially important for the brain, nerves and heart, which use a lot of glucose. Because the body stores only small amounts, people need a steady supply from food. Good sources include whole and enriched grains, pork, fish, beans, lentils, peas, nuts and seeds. In the US, many breads and cereals are fortified with thiamine.

What the research says

Thiamine deficiency is serious. MedlinePlus explains that a lack of thiamine can cause weakness, fatigue, confusion and nerve damage, and in severe cases a condition called beriberi or brain disorders known as Wernicke disease and Korsakoff syndrome. In the United States, deficiency is most often seen in people with heavy alcohol use, which makes it hard to absorb thiamine. People with poorly controlled diabetes, those who have had weight loss surgery and some older adults may also have lower thiamine levels.

For blood sugar, the evidence is early. In a small randomized, double-blind crossover trial, 12 people with impaired glucose tolerance or newly diagnosed type 2 diabetes took 300 mg of thiamine a day (3 doses of 100 mg) or placebo for 6 weeks. Thiamine lowered 2-hour glucose after a glucose tolerance test compared with baseline, while fasting glucose, insulin and insulin resistance worsened in the placebo phase but not on thiamine. The authors suggested high-dose thiamine might slow the progression toward diabetes, but the study was tiny and short, and larger trials are needed before drawing conclusions.

How it’s used in supplements

Thiamine is found in B-complex products, multivitamins, energy formulas and blood sugar supplements. Doses range from about the RDA to 100 mg or more. MedlinePlus notes there is no known poisoning linked to excessive thiamine intake, and the vitamin is generally considered safe because the body excretes what it does not need. Rare allergic reactions have been reported, mostly with injections. A 100 mg dose is far above daily needs but is common in supplements.

If you have diabetes, extra thiamine is unlikely to cause harm, but it should not be seen as a replacement for proven treatment. People who drink heavily or have symptoms such as numbness, confusion or unsteady walking need medical evaluation, because thiamine deficiency is treated with doctor-directed doses, sometimes by injection. Anyone taking several supplements should check labels, as many products contain overlapping B vitamins.