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Gut bacteria research in Japan shows hot springs reduce risk of some illnesses

Plumes of steam are seen rising from hot springs in Beppu, Oita Prefecture. (Mainichi/Junko Adachi)

BEPPU, Oita -- Onsen hot spring baths "have the effect of reducing risks of specific illnesses," according to a Dec. 15 interim report on experimental studies carried out by Kyushu University and the municipal government of this southwest Japan city and others regarding onsen hot springs' effect on immunity based on 40 test subjects' data.

    The university, based in the southwest Japan city of Fukuoka, says it intends to collect data on a total of 100 people by spring 2022, and publish its findings in papers submitted to international scholarly journals.

    A research group consisting of members of Kyushu University's Urban Institute and doctors at Kyushu University Beppu Hospital, among others, turned their attention to the huge variety of bacteria types that live inside people's intestines. By utilizing testing kits that make use of a database of 18,000 Japanese people's intestinal bacterial environments, the team is reportedly able to apply numerical values to the risks of easily developed conditions.

    Professor Shunsuke Managi, head of Kyushu University's Urban Institute, is seen announcing the results of the interim report at Hotel Shiragiku, in the city of Beppu, Oita Prefecture, on Dec. 15, 2021. (Mainichi/Toru Oshima)

    In the experimental study, to investigate what kinds of bacteria increase and decrease and in what way after bathing, the team took urine, blood and fecal samples from the 40 test subjects on the first day of the study. The subjects then bathed in specified onsen hot springs on a daily basis, and after a week their values were measured again.

    The results showed that a group of men who used simple onsen among the hot spring baths available in Beppu saw their risk of conditions including gout and irritable bowel syndrome reduce by 10% or more. Likewise, risks of liver diseases were also down by 10% or more for men taking sulfur hot spring baths. Women who used simple onsen baths reduced their risk of asthma and obesity by 10% or more. A group that entered hydrogen carbonate hot spring baths and chloride springs also saw their risk of a range of ailments fall, but none posted as much as a 10% reduction.

    Urban engineering professor Shunsuke Managi, who heads the institute, said: "Through differences in onsen type, gender and length of bathing time, we were able to put clear numerical values on specific intestinal bacteria's changes trending up or down. If we can increase our data by exceeding 100 cases, we'll very likely gain attention internationally. If we can medically prove the different effects on health from each of the different kinds of onsen hot spring in the city of Beppu, more people will stay here for extended periods," he said.

    (Japanese original by Toru Oshima, Beppu Local Bureau)

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