Vitamin B1, which is frequently called thiamine, is part of the B complex of water-soluble vitamins required for proper nutrition. Because vitamin B1 is water soluble, taking too much of it means the excess is flushed from the body in urine. As a result, overdosing on vitamin B1 is extremely rare. However, vitamin B1 may cause side effects, even when taken at low doses. As with any health supplement, you should consult your doctor before taking vitamin B1.
One reported symptom of taking too much vitamin B1 is an upset stomach. Breaking one large dose up into several smaller doses and spreading those throughout the day may reduce the risk of stomach upset. Taking vitamin B1 with food may also help.
In rare cases, vitamin B1 supplements can cause an allergic reaction. The most common symptom of an allergic reaction is skin irritation resulting in dry, itchy skin or a rash. Also in rare cases, a more severe reaction may occur, resulting in nausea, dizziness, shortness of breath and swelling of the hands, face, mouth or throat. If you or someone you know experiences severe swelling of the face and has difficulty breathing, contact emergency medical services immediately.
Imbalance of Other B Vitamins
The B vitamins all work together in a complex. Taking too much of a single B vitamin, such as vitamin B1, can cause an imbalance in the other B vitamins. In severe cases, the imbalance may cause deficiencies in the other B vitamins, which can cause a wide variety of symptoms. Deficiencies in several of the other B vitamins, such as B3, B6 and B12, can cause feelings of fatigue and tiredness, along with skin irritations and rashes. Deficiencies in B6 and B12 can lead to anemia, causing very pale skin and muscle weakness. Vitamin B12 deficiencies can also cause neurological symptoms, including numbness or tingling in the hands or feet.
The Recommended Daily Allowance, or RDA, of vitamin B1 for adults over the age of 19 is 1.2 mg per day for males and 1.1 mg per day for females. The doses for children and infants are smaller, down to 0.2 mg per day for infants younger than 6 months old. People with vitamin B1 deficiency may be prescribed larger doses to treat their condition. Vitamin supplements often contain 50 to 100 mg of vitamin B1. Because vitamin B1 is generally nontoxic, these doses are almost always safe.