Energy metabolism from carbohydrate and normal nerve function.
Switzerland age 18–65: 0.1 mg per MJ of energy intake.
Whole grains, legumes, pork, seeds, nuts and fortified foods.
Early fatigue, irritability and weakness; severe deficiency causes beriberi or Wernicke encephalopathy with neurological and cardiac signs.
Untreated severe deficiency can cause permanent brain injury or heart failure.
No specific hair or nail signs; confusion, gait or eye-movement abnormalities are urgent.
Chronic heavy alcohol use, severe malnutrition, bariatric surgery, persistent vomiting and refeeding.
In high-risk settings, clinical action matters more than waiting for a single test.
Food first; treat medically and promptly in high-risk or emergency settings.
Low toxicity from food and usual doses; no added benefit without need.