Vitamin B1 (Thiamine): Benefits, Deficiency Signs & Dosage

Thiamine (vitamin B1) is the coenzyme your body needs to convert carbohydrates into usable energy. Without it, glucose can't be fully metabolized through the citric acid cycle, and cells — especially neurons, which run almost entirely on glucose — start to run short of ATP. Unlike fat-soluble vitamins, thiamine isn't stored in meaningful reserves; the body holds roughly an 18-day supply, which is why deficiency can develop faster than people expect once intake drops or losses increase.

What Deficiency Actually Looks Like

Severe thiamine deficiency causes beriberi, historically seen in populations subsisting on polished white rice (thiamine is concentrated in the husk, removed during polishing). Wet beriberi affects the cardiovascular system — edema, tachycardia, eventual heart failure. Dry beriberi affects the peripheral nerves — numbness, tingling, muscle wasting, and gait disturbances.

The more clinically relevant deficiency syndrome in developed countries is Wernicke-Korsakoff syndrome, seen predominantly in chronic heavy alcohol use. Alcohol impairs thiamine absorption in the gut, reduces liver storage capacity, and interferes with the enzyme that converts thiamine to its active form. A 2020 review in Nutrients estimated that up to 80 percent of people with alcohol use disorder have some degree of thiamine deficiency, and Wernicke's encephalopathy — confusion, ataxia, and eye movement abnormalities — is a medical emergency that can progress to permanent memory impairment (Korsakoff psychosis) if not treated with immediate high-dose thiamine.

Who Else Is At Risk

Beyond alcohol use disorder, several groups run a meaningfully elevated risk of subclinical thiamine deficiency: people who've had bariatric surgery (reduced absorptive surface and lower food intake), people on long-term loop diuretics like furosemide (increased urinary thiamine loss), older adults with reduced dietary variety, people with hyperemesis gravidarum (severe pregnancy-related vomiting), and people with diets very high in refined carbohydrates and low in whole grains, legumes, and pork — thiamine's richest common food sources. Because early symptoms (fatigue, irritability, poor concentration, mild numbness) are nonspecific, subclinical deficiency is likely underdiagnosed outside these known risk groups.

Dosing

The RDA is 1.2mg/day for adult men and 1.1mg/day for adult women, easily met through a varied diet including whole grains, legumes, pork, and sunflower seeds. Standalone thiamine supplements are typically sold in 50–100mg doses — far above the RDA, but thiamine has a wide margin of safety since it's water-soluble and excess is excreted renally rather than accumulated. Clinical treatment of confirmed deficiency uses much higher doses, often 100–300mg administered by a physician, sometimes intravenously in acute Wernicke's cases; that's a medical treatment protocol, not a self-directed supplementation decision.

For most people without a specific risk factor, a food-first approach covers requirements without supplementation. For those in an at-risk group, a standard 100mg thiamine tablet or a B-complex that includes an adequate thiamine dose is a reasonable, low-risk addition — but if you suspect an existing deficiency rather than prevention, that's a conversation for a physician and possibly bloodwork, not a supplement aisle decision.

Forms: HCl vs. Benfotiamine vs. TTFD

Standard supplements use thiamine hydrochloride or thiamine mononitrate — both well-absorbed and inexpensive. Benfotiamine, a fat-soluble synthetic derivative, shows better bioavailability in some studies and has been researched specifically for diabetic neuropathy, though evidence there remains preliminary. TTFD (thiamine tetrahydrofurfuryl disulfide) is another fat-soluble form marketed for crossing the blood-brain barrier more efficiently; the research base is smaller and mostly limited to older Japanese studies, so it's reasonable to treat it as a plausible-but-unproven variant rather than a superior default.

Practical Takeaway

Thiamine deficiency is uncommon in people eating a varied diet with no elevated risk factors, and supplementation for its own sake — the "B1 for focus and energy" framing you'll see marketed broadly — isn't well supported for people who aren't actually deficient. Where it matters is identifying whether you fall into one of the known risk categories: heavy alcohol use, bariatric surgery history, chronic diuretic use, or a highly restrictive/refined diet. If any of those apply, thiamine is one of the more clear-cut cases in nutrition where a specific, well-studied deficiency has a specific, well-studied fix. A general B-complex covering thiamine alongside the other B vitamins is the more common practical choice, since deficiencies rarely occur in isolation.