Vitamin B1 (Thiamine)

Recommended Daily Intake

Recommended Dietary Allowance (RDA) for vitamin B1 for adult men is 1.2 mg/day, for women 1.1 mg/day, and 1.4 mg/day during pregnancy and breastfeeding ^[3].

Vitamin B1 Deficiency: Who is at risk?

• Chronic alcoholics who eat very little; alcohol also inhibits absorption of vitamin B1
• Rarely, individuals on fad diets or fasting or starving for a prolonged time, suffering from anorexia nervosa or severe psychological or physical stress, war refugees, individuals with celiac or Crohn’s disease, chronic diarrhea, gastric bypass (bariatric surgery for weight loss), hyperthyroidism, malaria, liver disease, burns, HIV/AIDS or cancer, diabetics with kidney damage, individuals on hemodialysis and older individuals with congestive heart failure on prolonged diuretic therapy
• In eastern countries, like Indonesia, Taiwan and Sri Lanka, deficiency, rarely, occurs in individuals eating only polished rice or cassava for a prolonged time, for example during fishing trips, and in babies breastfed by thiamine-deficient mothers.
• References: ^{[1,8,9,10,11,12,13]}

Diagnosis, Treatment and Prognosis

Vitamin B1 deficiency can be confirmed by a blood test. After a thiamine injection, symptoms usually improve within few hours and resolve completely within few days, but rarely in chronic Korsakoff psychosis ^[8]. Along with vitamin B1, other nutrients are often necessary:

• In the UK, ampules for intramuscular or intravenous injections with vitamin B1 (thiamine), B2 (riboflavin), B3 (niacin), B6 (pyridoxine), B9 (folate) and vitamin C are often used.
• In the US, a bag of intravenous fluids, called “banana bag,” or “rally pack,” containing vitamin B1 (thiamine), vitamin B9 (folate) and magnesium sulfate is often used ^[9].

Vitamin B1 Supplements

By mouth (available over-the-counter)

Water-soluble:

• Thiamine mononitrate (TMN)
• Thiamine hydrochloride (THCl)
• Thiamine pyrophosphate (TPP)

Fat-soluble:

Fat-soluble supplements provide higher blood thiamine concentrations than the water-soluble ones ^[31].

• Thiamine propyl disulfide (TPD) or prosultiamine
• Allithiamine naturally occurs in garlic; one of the synthetic forms is thiamine tetrahydrofurfuryl disulfide (TTFD) or fursultiamine
• Sulbutiamine can reach the brain in much greater amounts than other thiamine supplements ^[17]. Some small studies have suggested sulbutiamine could reduce fatigue (asthenia) but more research is warranted ^[36].

Benfotiamine

Benfotiamine is a synthetic thiamine, poorly soluble in water and fat; it can provide higher blood thiamine concentrations than water- and lipid-soluble forms ^[37]. In two small studies, oral benfotiamine reduced pain in individuals with diabetic ^[32] or alcoholic neuropathy ^[35].

Available oral thiamine forms

Oral thiamine is available alone as capsules, tablets (10-500 mg), softgels, lozenges, powder, liquid or as part of B-complex or multivitamin supplements.

NOTE: From the current scientific evidence it is not yet possible to conclude which of the above thiamine supplements is most effective.

Intramuscular injection (shot) and intravenous infusion

A thiamine hydrochloride injection into a muscle or infusion into a vein is used to treat severe acute vitamin B1 deficiency.

Recommended Thiamine Replacement Dosage for Adults

Healthy individuals on regular diets, including infants, pregnant and breastfeeding women and vegans can get sufficient amounts of thiamine by eating variety of foods, so they do not likely need thiamine supplements.

For individuals with suspected or confirmed vitamin B1 deficiency, various medical experts recommend very different doses of thiamine supplements:

• For mild deficiency without symptoms, tablets 5-30 mg/day ^[12]
• For chronic alcoholics with increased risk to develop deficiency, tablets up to 50 mg/day ^[12,23] or, intramuscular injections, 250 mg/day for several days ^[26]
• For a brain damage (Wernicke’s encephalopathy): intramuscular injections 15-300 mg/day or intravenous infusion 100-1,500 mg/day for few days, and then oral supplements 2.5-50 mg/day for several weeks until establishing the regular diet ^[25,26,38]
• During alcohol withdrawal, intramuscular injections, 250 mg/day for 3-5 days ^[38]

There is insufficient evidence about vitamin B1 supplements effectiveness in preventing or treatment of cancer, poor appetite, ulcerative colitis, Crohn’s disease, chronic diarrhea, HIV/AIDS, candida infections, congestive heart failure — CHF (except when caused by vitamin B1 deficiency), poor circulation, high blood pressure, atherosclerosis in diabetes mellitus, megaloblastic anemia (except in the thiamine-responsive type), blood clots, painful menstruation, multiple sclerosis, Alzheimer’s disease (dementia), Bell’s palsy, epilepsy, optic neuropathy, sciatic pain, cerebellar ataxia (muscle incoordination) after fever, memory loss, tinnitus, erectile dysfunction/low libido, DIDMOAD (Wolfram) syndrome, leg cramps in pregnancy, rheumatism (joint pain), gout, temporomandibular joint (TMJ) disorder, asthenia, fibromyalgia, chronic fatigue syndrome (CFS), low back pain, insomnia, stress, aging, canker sores, depression, stuttering or pyruvate dehydrogenase deficiency; its effectiveness in improving athletic performance, weight loss or as a mosquito repellent has also not been proven ^{[1,6,12,24,33]}.

Vitamin B1 supplements probably do not help in hip fractures, skin disorders, nerve repair in peripheral neuropathy (except when caused by vitamin B1 deficiency) or hangover (which is not associated with vitamin B1 deficiency, so there is no reason why vitamin B1 patch should work) ^[12].

Can vitamin B1 supplements be bad for you? Side Effects, Risks

In general, thiamine supplements are safe to use. No side effects have been reported even after very high doses (1,500 mg of thiamine by mouth), so overdose is practically impossible ^[31]. Excessive thiamine is lost with urine. No tolerable upper intake level (UL) for thiamine has been set ^[1].

Vitamin B1 toxicity. In few cases, severe allergic reactions (anaphylactic reactions with itchy skin, swollen face, difficult breathing, low blood pressure or even death) occurred after repeated intravenous infusions but not after oral intake ^[28].

Thiamine safety in pregnancy

The U.S. Food and Drug Administration (FDA) lists thiamine in doses within Recommended Daily Allowance (1.4 mg/day) as pregnancy category A, which means no harm for the babies in human trials have been observed, and doses above 1.4 mg/day as category C, because insufficient human studies have been done to prove its safety at these doses ^[18,23]. In conclusion, thiamine in pregnancy should be used only when the deficiency is suspected.

Vitamin B1 Interactions With Drugs and Foods

The following medications can lower the blood concentration of thiamine: antacids, diuretics, the prolonged use of the anticonvulsant phenytoin, birth control pills, certain antibiotics, sulfa drugs and the chemotherapeutics 5-fluorouracil and methotrexate ^[1,8].

Alcohol and anti-thiamin factors in foods, like raw freshwater fish, raw shellfish, ferns, African silkworms (in Nigeria), areca (betel) nuts, horsetail, when consumed in large amounts, can inhibit thiamine absorption ^[1,19].

Folate and magnesium deficiency, which are both common in alcoholics, reduce thiamine activity in the body ^[1,8].

Glucose infusion may, in alcoholics or individuals after prolonged starvation, trigger acute vitamin B1 deficiency (Wernicke encephalopathy), a part of refeeding syndrome.

Vitamin B1 Absorption and Body Stores

• Site of absorption: mainly in the upper small intestine (jejunum)
• Vitamin B1 is a water-soluble vitamin, which does not dissolve in the body fat, so the body stores are depleted within 1 month of cessation of the vitamin intake.
• References: ^[1,8]

Frequently Asked Questions

1. What are thiamine mechanism of action and main functions ?

Thiamine acts as an activating molecule (cofactor, coenzyme) for the enzymes involved in the breakdown of carbohydrates and proteins and thus enables the release of energy from them ^[1]. Thiamine is especially important for proper functioning of the nerves, brain, muscles and heart. Thiamine is also involved in the production of gastric acid, neurotransmitters GABA and acetylcholine, maintaining the myelin nerve sheaths and in breakdown of alcohol.

2. Which vitamin gives you more energy: B1, B6 or B12?

Vitamins B1, B6 and B12 do not give you energy because they do not contain calories but make your body able to produce energy. When you are deficient in vitamin B1, B6 or B12, your body is less able to produce energy so appropriate vitamin B supplements will restore this ability, but when you have normal blood levels of these vitamins, vitamin B supplements will not likely boost your energy.

3. What are the benefits of high-dose thiamine supplements?

• High thiamine doses in the form of intramuscular or intravenous injection are necessary to provide high concentrations of thiamine in the brain in treatment of acute brain damage caused by severe thiamine deficiency ^[26].
• High doses (>300 mg/day) of oral benfotiamine have been reported to be more effective in treatment of peripheral neuropathy than lower doses (150 mg/day) ^[17].

4. Does vitamin B1 cause yellow urine?

It is not vitamin B1 but vitamin B2 (riboflavin) (and beta-carotene and vitamin C), which gives the urine bright yellow color ^[2].