Onsen bathing is really good for you (study)

A study has found that onsen bathing in the evening hours is linked to lower prevalence of hypertension in older adults

A new study has found that onsen bathing in the evening hours is linked to lower prevalence of hypertension in Japanese adults over 65.

In 1931, Kyushu University founded the Onsen Therapy Research Institute in the historical city of Beppu to study the therapeutic benefits of onsen, which are Japan’s natural hot springs and the bathing facilities and traditional inns around them. The use of hot springs can be traced as  far back as ancient Egypt, more than 5,000 years ago and onsen are referenced in Japan’s oldest books and creation myths. Beppu is one of the country’s most famous hot spring resorts, producing more hot spring water than any other in the country. 

Over the last 90 years, the Onsen Therapy Research Institute has expanded to cover a wider range of medical fields including internal and external medicine, rehabilitation, gynecology, and cardiology, but still conducts research on the health benefits of onsen.

Researchers at the institute and Kyushu University’s Beppu Hospital published a paper in Scientific Reports using data from a 2011 survey of more than 11,000 people. 

“In 2011, the institute partnered with the city and conducted a massive survey of Beppu residents over 65 about their health and onsen habits,” said Satoshi Yamasaki, first author of the study, according to a research brief. “This is something we can uniquely do here in Beppu because onsen are a part of everybody’s daily lives, especially for the elderly. There are local onsen facilities everywhere, and you can even connect onsen to your home utilities.”

The survey collected information from Beppu residents regarding their medical history and onsen habits.

“I wanted to find out if long-term onsen bathing had any preventative effects on hypertension. Past research has shown that traditional thermal therapy and hot spring bathing are effective against various diseases including hypertension,” said Yamasaki. “In Japan especially, it is the leading cause of hospital visits and long-term prescription medication use.”

The team pulled out 4,001 individuals who currently have, or have a history of, hypertension. Their first analysis found that hypertension was correlated with increased likelihood of history of other pathologies.

“These were the usual suspects of pathologies correlated with hypertension such as gout, arrhythmia, renal disease, and diabetes,” Yamasaki said. “But it was when we looked at an individual’s onsen habits that we found something interesting. We found that individuals who bathed in onsen after 19:00 were roughly 15% less likely to have hypertension.”

The team hypothesizes that the two main reasons for these findings are lower stress and faster sleep onset. Previous research has found that faster onset of sleep is associated with better sleep quality and improved hypertension control. Moreover, thermal therapies like sauna bathing have been shown to alter levels of stress markers in the blood and lead to better mitigation of hypertension.

Yamasaki notes that their study has limitations. “We also could not account for the respondent’s daily lifestyle that could affect hypertension, or if they are being treated for hypertension medically or with onsen. Nonetheless, we found that habitual nighttime onsen bathing was associated with a lower prevalence of hypertension. To understand these results further, we will need more data from patients.”

On the subject of saunas, a study released in 2016 found that taking a sauna at least twice a week was correlated with significantly reduced risk of asthma, other chest ailments, infections, dementia-related illnesses, sudden cardiac death, and cardiovascular and all-cause mortality.


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