Sauna, a tradition in many Nordic countries especially in Finland, has recently enjoyed a renewed status as a biohack that not only makes us feel good, but also is good for us, improving and optimizing various aspects of our mental and physical health, such as cardiovascular health, mood disorders and recovery from exercises. Indeed, I’m bummed that in Sweden, my current country of residence, this wonderful tradition is not nearly as ubiquitous as in Finland, my previous Nordic residence. Previously, I was trying to convince my Swedish fiancé to upgrade our home with a proper dry sauna, or at least an infrared sauna, to not miss out this seemingly omnipotent biohack.
They are notoriously expensive though, costing easily thousands of euros. Also, they require space, a deal-breaker if you live in an apartment, like we do, rather than a detached house. As the realization set down that moving to a large house just to enable occasional sauna sessions probably is an unwise and unnecessary extravaganza, I took a serious look at another wonderful tradition from my home country, Japan – nyuyoku i.e. whole-body immersion hot bath.
Both sauna and hot bath take an advantage of the heat’s beneficial effects. One of the best-known benefits of heat immersion is improved vascular functions, such as decreased blood pressure and improved arterial stiffness . Heat immersion can also act as an effective exercise mimetic, upregulating nitric oxide synthesis and increasing angiogenesis, great news to those with an injury preventing pulse-raising activities. To my great joy, studies demonstrate similar health benefits across different heat-delivery methods, and in a 2018 paper, a group of Japanese researchers reported that habitual hot-water bathing has protective effects on cardiovascular health, like these achieved with dry sauna .
Not only matching the benefits of sauna, immersive bath has some unique benefits, such as water pressure and buoyancy . Researchers who are proponents of whole-body immersion bathing tend to underline these additional benefits, like increased cardiac output and increased metabolism induced by water pressure .
For a homebrewing biohacker like myself, however, hot bath’s greatest edges probably are its availability and “stack-ability” i.e. hot bath can be stacked with many other biohacks. Let’s explore how we can stack a hot bath to upgrade it to a next level super-biohack.
No story of bathing in Japan will be complete without a mention of the ancient tradition onsen, a whole-body immersion hot bath in therapeutic spring water. It’s such an important tradition that a federal law onsen hou regulates it, requiring that any water source that calls itself a legal onsen satisfy criteria such as the presence of certain minerals and/or other therapeutic agents at specific concentrations. For instance, manganese, bromine, and irons are onsen-making minerals at specific concentrations.
At home, many Japanese add bath salts to their bathtub, such as this one and this one, containing mineral blends like these found in well-known onsens. Some onsen waters are also drinkable, and many believe that the oral intake has additional health benefits. While I’m unaware of a scientific evidence supporting the believe for oral onsen consumption, benefits of mineral absorption through the skin are thoroughly documented, making it a great stacking strategy to spike your bath water with a high-quality onsen bath salt.
Also, some gases and even certain types of radiation are recognized as one of 19 onsen-making therapeutic agents. My current bathing routine involves a mineral-rich onsen bath salt combined with molecular hydrogen bath tablets. I’m a big fan of hydrogen water and have tried many different products as well as different ways of administrations. I started adding hydrogen tablets to my hot bath after learning that Dr. Ohta, the chief author of the 2007 Nature Medicine paper  that triggered the increased interests in hydrogen as a therapeutic molecule, is a big proponent of hydrogen bath and that just a 7-minutes of immersion in hydrogen gas-rich water is shown to increase the body’s hydrogen level.
The triple-stacks with heat, minerals, and hydrogen gas make me feel golden every evening when I take a half-an-hour or so hot bath! Nevertheless, I’m curious to further add a radiation therapy to my already well-stacked hot bath practice. Since an American researcher Dr. Luckey’s 1980 publication “Hormesis With Ionizing Radiation”, describing hormesis effects of a low-level radiation, over 3,000 scientific research papers have demonstrated low irradiation’s benefits across species including humans . Among the benefits are increased SOD (super oxide dismutase), increased GPx (glutathione peroxidase), and an increase in T immune cells. In Japan, onsens with a low level of radon have been appreciated as therapeutic over 1,000 years, and today, pieces of rock from these onsens are available for purchase, to recreate the beneficial irradiation at home.
So, I’m feeling ok without sauna at home after all. Though it’d be nice to have one, the researches seem to point to that hot bath is at least as good a biohack, with the bonus of multiple stacking possibilities!
 Luckey T.D. Hormesis with Ionizing Radiation. Boca Raton: CRC Press, Inc.; 1980.