In fall of 2014, when a young man in his 20s died mysteriously in Kyushu, Japan, authorities ordered an investigation into the cause of his death.
Now, the details of the death of an otherwise healthy man have been revealed.
Dr. Shinichi Kubo, a professor of forensic medicine at Fukuoka University, is pronouncing that the man’s death is Japan’s first verified case of lethal day-to-day caffeine consumption, reported Newser.
The man’s death is considered unintentional because there were no signs of deliberate overdose, according to Japan Times.
"We had never heard of fatal caffeine intoxication," the Health, Labour and Welfare Ministry said.
The man, who worked at a 24-hour gasoline station from midnight to dawn, had vomited several times in the year before his death. Vomiting can be a sign of caffeine intoxication, according to Japan Times.
The actual amount of caffeine he ingested on the day of his death and on a daily basis is unknown. But a small amount of alcohol and a high concentration of caffeine in his stomach, suggesting caffeine tablets, as well as the remnants of a pill, were found in his system.
Fukuoka University concluded the drinks — mostly energy drinks — were likely what killed him. The school wasn't legally allowed to run broad tests on the pill.
According to the The Wall Street Journal, the lethal quantity of caffeine consumption in a day is 140 8-ounce cups of coffee, containing 14,000 mg of caffeine, although U.S. Food and Drug Administration warns that ingesting even 600 mg, equal to about four to seven cups of coffee, is dangerous.
In the United States, caffeine overdoses have been documented before. In 2014, a high school prom king died of caffeine overdose right before graduation, Newser reported.