Causes
Beriberi is caused by a lack of thiamine (vitamin B1). Thiamine occurs naturally in unrefined cereals and fresh foods, particularly whole grain bread, fresh meat, legumes, green vegetables, fruit, milk, etc. Beriberi is therefore common in people whose diet excludes these particular types of nutrition e.g. as a result of famine.
Beriberi may be found in people whose diet consists mainly of polished white rice, which is very low in thiamine because the thiamin-bearing husk has been removed. It can also be seen in chronic alcoholics (Wernicke-Korsakoff syndrome), Arsenic poisoning causes alterations in cellular metabolism resulting in blockage of thiamine use which results in thiamine deficiency without any dietary shortfall. The mechanism of arsenic neuropathy may be similar to the neuropathy of thiamine deficiency, whereby arsenic inhibits the conversion of pyruvate to acetyl coenzyme A and thus blocks the Krebs cycle.
The disease was often found in Asian countries (especially in the 19th century and before), due to those countries' reliance on white rice as a staple food.
Thiamine deficiency causes neuropathy through neuron death due to its effects upon astrocytes. This causes alterations in their glutamate uptake, through changes in the levels of the astrocytic glutamate transporters EAAT1 and EAAT2 creating excitotoxicity. Other changes include those to the GABA transporter subtype GAT-3, GFAP, glutamine synthetase, the water channel protein Aquaporin 4. These create lactic acidosis, brain edema, oxidative stress, inflammation, and white matter impairment.
A rare condition known as genetic beriberi is passed down through families. People with genetic beriberi lose the ability to absorb thiamine from foods. This can happen slowly over time and symptoms occur when the person is an adult. However, because doctors may not consider beriberi in non-alcoholics, this diagnosis is often missed.
Beriberi can occur in breast-fed infants when the mother's body is lacking in thiamine. The condition can also affect infants who are fed unusual formulas that don't have enough thiamine.
Getting dialysis and taking high doses of diuretics can raise the risk of beriberi. It is also occasionally diagnosed in patients having undergone roux-en-y gastric bypass or other enteric diversion weight-loss surgery.
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