Some extracts:
In 1877, Japan’s Meiji Emperor watched his aunt, the princess Kazu, die of a common malady: kakke. If her condition was typical, her legs would have swollen, and her speech slowed. Numbness and paralysis might have come next, along with twitching and vomiting. Death often resulted from heart failure.The emperor had suffered from this same ailment, on-and-off, his whole life. In response, he poured money into research on the illness. It was a matter of survival: for the emperor, his family, and Japan’s ruling class. While most diseases ravage the poor and vulnerable, kakke afflicted the wealthy and powerful, especially city dwellers. This curious fact gave kakke its other name: Edo wazurai, the affliction of Edo (Edo being the old name for Tokyo). But for centuries, the culprit of kakke went unnoticed: fine, polished, white rice.Gleaming white rice was a status symbol—it was expensive and laborious to husk, hull, polish, and wash. In Japan, the poor ate brown rice, or other carbohydrates such as sweet potatoes or barley. The rich ate polished white rice, often to the exclusion of other foods.This was a problem. Removing the outer layers of a grain of rice also removes one vital nutrient: thiamine, or vitamin B-1. Without thiamine, animals and humans develop kakke, now known in English as beriberi. But for too long, the cause of the condition remained unknown....By 1877, Japan’s beriberi problem was getting really serious. When the princess Kazu died of kakke at 31, it was only a decade after her former husband, Japan’s shogun, had died, almost certainly from the mysterious disease. Machine-milling made polished rice available to the masses, and as the government invested in an army and navy, it fed soldiers with white rice. (White rice, as it happened, was less bulky and lasted longer than brown rice, which could go rancid in warm weather.) Inevitably, soldiers and sailors got beriberi.No longer was this just a problem for the upper class, or even Japan. In his article British India and the “Beriberi Problem,” 1798–1942, David Arnold writes that by the time the emperor was funding research, beriberi was ravaging South and East Asia, especially “soldiers, sailors, plantation labourers, prisoners, and asylum inmates.”
Go read the whole article, at Atlas Obscura, to read about the experiments that found a solution.