Vitamin B1, or thiamine, is a water-soluble micronutrient that humans cannot synthesize endogenously and must obtain through diet or supplementation. It was first isolated in 1926 and holds distinction as one of the first vitamins to be chemically identified. Thiamine is found in a variety of whole foods but is easily depleted by alcohol consumption, certain medications, high carbohydrate intake without adequate B-vitamin intake, and prolonged cooking of food.

Thiamine functions primarily as the active coenzyme thiamine pyrophosphate (TPP), which is a required cofactor for key enzymes in carbohydrate metabolism, including pyruvate dehydrogenase and alpha-ketoglutarate dehydrogenase in the Krebs cycle. These enzymes are critical for ATP production, and their impairment during thiamine deficiency results in cellular energy failure, particularly in the nervous system and heart, which have high energy demands. Additionally, thiamine supports the pentose phosphate pathway via transketolase, important for nucleotide synthesis and antioxidant defense through NADPH production.

Oral thiamine hydrochloride is adequate for dietary supplementation and mild deficiency correction. Benfotiamine capsules (typically 150–300 mg/day) are preferred for neuropathy applications due to higher bioavailability. Parenteral (IV or IM) thiamine is the standard of care for acute deficiency states such as Wernicke's encephalopathy. Sublingual forms are available but have limited clinical trial data compared to oral and injectable forms.

• Thiamine Deficiency (Beriberi / Wernicke's Encephalopathy)
• Diabetic Neuropathy
• Alcohol-Related Neuropathy
• Heart Failure
• Fatigue / Low Energy

• Wernicke's Encephalopathy (in alcohol-use disorder or post-bariatric surgery patients with known thiamine depletion risk)
• Beriberi (in populations with thiamine-poor diets or malabsorption conditions)
• Thiamine deficiency-related cardiac dysfunction in long-term loop diuretic users

• Nutritional Yeast — One of the highest thiamine concentrations per serving among foods; 2 tablespoons can provide 100–640% of the RDA depending on the brand's fortification, making it an exceptionally efficient dietary source.
• Pork (lean cuts, especially pork loin) — Among the richest whole-food animal sources of thiamine; a 3 oz serving of pork tenderloin provides approximately 0.8–1.0 mg of thiamine, covering roughly 70–85% of the adult RDA.
• Sunflower Seeds — A quarter-cup of sunflower seeds provides approximately 0.5 mg of thiamine, making them one of the best plant-based whole-food sources and a practical snack for boosting daily intake.
• Legumes (Black Beans, Lentils, Navy Beans) — Cooked legumes provide 0.2–0.4 mg thiamine per half-cup serving and are a staple thiamine source in plant-based diets; navy beans are particularly concentrated among legume varieties.
• Whole Grains (Brown Rice, Oats, Whole Wheat) — Whole grains retain the thiamine-rich bran and germ layers that are removed in processing; a serving of oats provides approximately 0.2–0.3 mg thiamine, and fortified refined grains are also a major population-level source.

• Mild nausea or gastrointestinal upset at high oral doses (uncommon)
• Skin irritation or flushing at injection site (with IM/IV administration)
• Rare hypersensitivity or anaphylactic reaction (primarily with rapid IV infusion)
• Harmless yellow discoloration of urine at high supplemental doses (due to riboflavin co-excretion in B-complex products; not thiamine-specific but common with B-vitamin supplements)

• Recommended daily: Dietary Reference Intake (DRI): 1.1 mg/day (women), 1.2 mg/day (men). Therapeutic supplementation for neuropathy: Benfotiamine 150–300 mg/day. Deficiency correction (oral): 50–100 mg/day of thiamine HCl. Acute Wernicke's encephalopathy: 200–500 mg IV thiamine 3x/day (clinical setting only).
• Best time of day: Can be taken at any time of day; some individuals prefer morning to align with the metabolic energy-supporting role of B-vitamins, though no specific timing advantage has been demonstrated clinically.
• With or without food: Oral thiamine is generally well absorbed with or without food. Taking with a meal may reduce the rare occurrence of mild GI discomfort and is a reasonable default recommendation.
• Time to effect: Deficiency-related symptoms (fatigue, sensory changes) may begin improving within days of correcting severe deficiency; neuropathy symptom reduction with benfotiamine typically requires 6–12 weeks of consistent use.
• How long to take it: For dietary supplementation or mild deficiency support, long-term daily use is appropriate and safe. For therapeutic neuropathy protocols (benfotiamine), trials of 8–12 weeks are standard; continuation should be guided by symptom response. Patients on loop diuretics or with alcohol use disorder may require indefinite supplementation under medical supervision.