Why did polished white rice contribute to beriberi outbreaks?

Polished white rice contributed to outbreaks of beriberi because the milling process removes the outer layers of the grain, where thiamin (vitamin B1) is concentrated.12

Thiamin is an essential vitamin that acts as a coenzyme in carbohydrate metabolism. When individuals rely on a diet consisting primarily of polished white rice, they do not receive sufficient amounts of this nutrient. In the absence of thiamin, metabolic byproducts like pyruvic acid and lactic acid accumulate in the tissues, leading to the nerve damage and heart failure characteristic of beriberi.132

Historically, this deficiency was common in populations where white rice was a dietary staple. The incidence of the disease has since decreased due to more varied diets, the consumption of parboiled or enriched rice, and the addition of synthetic thiamin to food supplies.123