Evening soaks in hot springs have long been linked to cardiovascular benefits in Japanese communities, a relationship researchers at Kyushu University began to explore with careful study. Beppu, a coastal city along Kyushu’s northeast, is famous for its abundance of onsen, geothermal baths that are woven into daily life and cultural practice. Locals have long regarded these natural waters as a form of traditional medicine, with regular visits intertwined with routines that balance body, mind, and seasonal rhythms.
To investigate whether these springs genuinely support health, scientists from Kyushu University designed a large-scale survey. They collected comprehensive information from more than 11,000 participants, including medical histories, lifestyle habits, and detailed data about which types of onsen people visited. The sample represented a significant portion of Beppu’s older adults, with roughly one in three residents aged 65 and above contributing to the study. Within the group, about 4,001 individuals had hypertension, offering a meaningful subset to examine potential associations between onsen use and blood pressure management.
The analysis revealed a notable association: individuals who bathed in onsen after 7 pm were about 15 percent less likely to have hypertension compared to those who did not engage in late-evening soaks. The researchers proposed two plausible explanations for this pattern. First, the warm water may promote more relaxed sleep onset, a factor linked to lower blood pressure and improved vascular function over time. Second, the heat and immersion involved in hot procedures such as saunas or prolonged baths can upregulate physiological responses that reduce circulating stress markers, potentially contributing to better cardiovascular health in the long run. Moreover, late-evening onsen use might encourage healthier daily rhythms, including more consistent relaxation periods before night, which can support overall heart health. The study underscores how familiar cultural practices can intersect with measurable health outcomes, inviting further exploration into how routine experiences like onsen bathing fit into broader strategies for cardiovascular wellness across diverse populations.