Is it time to heat things up a bit for our health?

I had such a frigid response to my previous article about cold immersion therapy that I thought I would heat things up this time. Bad puns aside, are there benefits to owning and regularly using a hot tub or sauna? (Full disclosure, I own a hot tub and it brings me great joy.) Many cultures incorporate regular use of passive heat therapies: Japanese Onsen, Finnish/Swedish saunas and Turkish Hammam are just a few. But the question is: are the benefits from these therapies noticeable with one time use, or do they need to be routine? And are there any risks involved? Hopefully this article will answer those questions and not cause a heated debate in the comment section. (Editor's note: 😫 🛑) The first style of regular heat therapy is the Finnish style sauna. This is the cedar/wood-lined room with a hot rock heater and bucket of water to throw on the rocks. Temperatures range from 80C to 100C and humidity from 10%-20%.1 Regular usage is considered to be 2-3 times a week for around 11-19 minutes each session. One prospective cohort study found that regular Finnish sauna bathers had a reduced risk of all-cause mortality and various CVD events (sudden cardiac death , fatal coronary heart disease (CHD) , fatal cardiovascular disease). Protection was increased with greater frequency and longer duration. The risk of fatal CHD events was 23% lower for those taking 2- 3 saunas per week and 48% lower for users taking 4- 7 saunas per week One limitation of this study was that it followed middle-aged men only (42-60 years). One possible mechanism for this benefit is that heart rates can increase to 100-150 beats/min during hot saunas.2 This is thought to mimic the cardiovascular benefits of low-moderate intensity physical exercise, as increased skin blood flow leads to higher cardiac output. Another prospective cohort study in Finland followed 2300 middle aged men for 20 years with regards to their regular sauna use and health benefits.3 It was noted that increased frequency of sauna use was associated with a reduced risk of all-cause mortality, sudden cardiac death, fatal coronary heart disease and fatal cardiovascular disease. The reasons for these benefits were thought to be due to lower blood pressure and enhanced left ventricular function. Again, the increases in temperature are thought to mimic low to moderate-intensity exercise training. Hot tubs are also a form of passive heat therapy. In one cross-sectional study, self reported hot tub users with type 2 diabetes experienced health benefits compared to non-hot tub users.4 Hot tub users had slightly better A1C readings, and lower diastolic blood pressure and BMI compared to non-hot tub users. What was also interesting in this study was that patients were studied by how often they used hot tubs. Patients who used their hot tub more than 4 times a week had better health markers (A1C, DBP ) that those that used a hot tub once weekly or less. Also of note was that the more often you used a hot tub the less likely you were to be prescribed a GLP-1 receptor agonist. Association is not causation, but it is still an interesting finding. Similar benefits were noted in a large (30,000 subjects) group of middle aged Japanese subjects. The majority of participants used a hot tub daily (72%). Hot tub frequency was inversely associated with incidence of CVD.5The researchers did note that regular hot tub users were in a higher socioeconomic class, but this did not affect findings. What about single sessions of passive heat therapy, are there any health benefits? It appears that single sessions are not effective for those individuals with T2D. In one small study, 12 patients with T2DM did a single infrared sauna session for 40 min before a 2 hour OGTT.6 There were no improvements in glucose handling in this study. Another meta-analysis confirmed these results.7Are there any risks with regular passive heat therapy? You can probably guess the risks associated with hot tub/spa use. There is the risk of infectious disease/death, with Legionella being the most prominent.8 But eight deaths in the United States over 15 years (between 2000-2014) seems pretty low. Undiagnosed arrhythmia is another concern. Most of the hot tub- and spa-related injuries are the result of “slips and falls” associated with wet surfaces and/or drug/alcohol use.9,10 Hopefully this article warmed you up to the idea of the health benefits of regular passive heat therapy. If nothing else, a good soak in a hot tub is relaxing. References: Cardiovascular and Other Health Benefits of Sauna Bathing: A Review of the Evidence. Laukkanen, Jari A. et al. Mayo Clinic Proceedings, Volume 93, Issue 8, 1111 - 1121.Taggart P, Parkinson P, Carruthers M. Cardiac responses to thermal, physical, and emotional stress. Br Med J. 1972 Jul 8;3(5818):71-6. doi: 10.1136/bmj.3.5818.71. PMID: 4114377; PMCID: PMC1785579.Laukkanen T, Khan H, Zaccardi F, Laukkanen JA. Association Between Sauna Bathing and Fatal Cardiovascular and All-Cause Mortality Events. JAMA Intern Med. 2015;175(4):542–548. doi:10.1001/jamainternmed.2014.8187Katsuyama H, Hakoshima M, Adachi H, Masui Y, Sako A, Inokuma S, Yanai H. Habitual Hot-Tub Bathing and Cardiovascular Risk Factors in Patients With Type 2 Diabetes Mellitus: A Cross-Sectional Study. Cardiol Res. 2022 Jun;13(3):144-153. doi: 10.14740/cr1371. Epub 2022 Jun 16. PMID: 35836731; PMCID: PMC9239506.Ukai T, Iso H, Yamagishi K, Saito I, Kokubo Y, Yatsuya H, Muraki I, Eshak ES, Sawada N, Tsugane S. Habitual tub bathing and risks of incident coronary heart disease and stroke. Heart. 2020 May;106(10):732-737. doi: 10.1136/heartjnl-2019-315752. Epub 2020 Mar 24. PMID: 32209614.Schenaarts L, Hendriks FK, Fuchs CJ, Sluijsmans WE, Snijders T, van Loon LJ. A Single Sauna Session Does Not Improve Postprandial Blood Glucose Handling in Individuals with Type 2 Diabetes Mellitus: A Cross-Over, Randomized, Controlled Trial. Exp Clin Endocrinol Diabetes. 2024 Nov;132(11):622-630. doi: 10.1055/a-2406-4491. Epub 2024 Aug 29. PMID: 39209309; PMCID: PMC11560331.Maley MJ, Hunt AP, Stewart IB, Faulkner SH, Minett GM. Passive heating and glycaemic control in non-diabetic and diabetic individuals: A systematic review and meta-analysis. PLoS One. 2019 Mar 22;14(3):e0214223. doi: 10.1371/journal.pone.0214223. PMID: 30901372; PMCID: PMC6430508.Hlavsa MC, Cikesh BL, Roberts VA, Kahler AM, Vigar M, Hilborn ED, Wade TJ, Roellig DM, Murphy JL, Xiao L, Yates KM, Kunz JM, Arduino MJ, Reddy SC, Fullerton KE, Cooley LA, Beach MJ, Hill VR, Yoder JS. Outbreaks Associated with Treated Recreational Water - United States, 2000-2014. MMWR Morb Mortal Wkly Rep. 2018 May 18;67(19):547-551. doi: 10.15585/mmwr.mm6719a3. PMID: 29771872; PMCID: PMC6048947.Dahiya R, Asif M, Santhi SE, Hashmi A, Ahadi A, Arshad Z, Nawaz F, Kashyap R. Unveiling Lethal Risks Lurking in Hot Tub Baths: A Review of Tragic Consequences. Cureus. 2024 Feb 14;16(2):e54198. doi: 10.7759/cureus.54198. PMID: 38496149; PMCID: PMC10940967.Alhajj M, Nelson NG, McKenzie LB. Hot tub, whirlpool, and spa-related injuries in the U.S., 1990-2007. Am J Prev Med. 2009 Dec;37(6):531-6. doi: 10.1016/j.amepre.2009.08.024. PMID: 19944920.