- Vitamin B1 (Thiamine) deficiency leads to beriberi, a disease characterized by impaired carbohydrate metabolism affecting the nervous and cardiovascular systems.
- Thiamine acts as a crucial coenzyme for enzymes in the pyruvate dehydrogenase complex and the α-ketoglutarate dehydrogenase complex, essential for energy production.
- Its deficiency results in accumulation of pyruvic acid and lactic acid, causing neuronal damage and cardiovascular dysfunction.
- Clinically, beriberi presents in two forms: dry beriberi with peripheral neuropathy and muscle wasting, and wet beriberi with high-output cardiac failure and edema. Prompt thiamine supplementation reverses the symptoms.

Reference: Davidson’s Principles and Practice of Medicine, 24th Edition, Chapter: Nutrition and Metabolic Disorders, Page 628.