Since 1931, researchers have been investigating the therapeutic effects of Japanese hot springs, also known as ‘onsen.’ In 2011, the hospital conducted a massive survey of Beppu residents over 65 on their ‘onsen’ habits and health. One result they found was that onsen bathing after 19:00 is linked to a lower prevalence of hypertension. The research team hypothesizes two reasons for such results: lower stress and faster sleep onset.