People love coffee, but some folks don't want the feeling caffeine leaves behind. In previous centuries, drinking coffee and other sources of caffeine was considered indulgent and sometimes downright sinful. Decaf offered a guilt-free way to drink coffee. German coffee roaster Ludwig Roselius developed a method of removing the caffeine from coffee in 1905 and sold his decaf under the name Kaffee HAG. It was marketed as a healthy alternative to coffee, and was adopted by the health and fitness craze sweeping Germany in the 1920s and '30s. The Nazis got into the act, too.
Under the Nazi Party, the appeal of decaf (a way to avoid stimulants) became state policy meant to safeguard the idolized Aryan race. Geoffrey Cocks, author of The State of Health: Illness in Nazi Germany, says that Nazis “earnestly believed that it was their duty and their responsibility not only to protect health of individual Germans, but the health of the entire German people as a biological, racial entity.” This of course excluded Jews and other non-Aryans, as well as homosexuals and the sick.
Similarly, the Party took measures to warn the Aryan population of caffeine’s dangers. A 1941 Hitler Youth Handbook, writes Stanford science historian Robert Proctor, states that “for young people at least, caffeine was a poison ‘in every form and in every strength.’” By the end of the 1930s, he adds, decaffeinated coffee was “widely available—and strictly regulated.”
There's a punch line to the era of Nazis drinking Kaffee HAG for their health. You can read the entire story at Atlas Obscura.