Beriberi is caused by an infectious agent or toxin associated with rice.

Beriberi was especially common where polished white rice dominated the diet, but that association did not initially point cleanly to deficiency. In the bacteriological era, infection was an obvious suspect, and some researchers instead imagined a toxin in the rice. Christiaan Eijkman himself first interpreted his famous chicken experiments in toxic terms after birds fed polished rice developed a paralysis-like illness and recovered when rice bran was restored.

The more radical interpretation was that something necessary had been removed. Gerrit Grijns argued that the outer layers of rice supplied an essential protective substance, helping shift the problem from poison to missing nutrient. Work on dietary “accessory factors” followed, and the protective compound was eventually identified as vitamin B1, or thiamine.

The transition was gradual rather than a single eureka moment. Modern beriberi can arise from inadequate intake, alcoholism, malabsorption, prolonged vomiting, dialysis, and other conditions that leave the body short of thiamine.