Improving Healthspan with Intermittent Thermal Stress


Many people are aware of the benefits of reducing chronic stress, but most people don’t know that there’s actually a good type of stress, said Rhonda Patrick, PhD, at the Institute for Functional Medicine (IFM) Annual International Conference (AIC) in Orlando, Florida.

Often referred to as "new stress," intermittent exposure to this form of stress can increase health outcomes and promote longevity, according to Patrick, a published scientist and health educator who studies systems biology and various non-pharmacological interventions.

In her presentation, Patrick discussed an integrative intervention growing in popularity that involves exposure to intermittent stressors, specifically thermal stress, through saunas and cold exposure.

Whether it was fasting due to food scarcity, intense physical activity to catch prey, or digestion of phytochemicals from plants consumed, “throughout human evolution, we have been exposed to intermittent types of challenges,” said Patrick. “These intermittent challenges, we have adapted to them, and we have genetic pathways that are meant to be turned on through them.”

Commonly called stress response pathways, Patrick explained that when these genetic pathways are turned on, various genes are activated. She said many of the activated genes then trigger beneficial anti-inflammatory and antioxidant effects that promote repair processes.

“There's a lot of crosstalk between these genetic pathways,” said Patrick. “So, for example, the phytochemicals can activate the same pathways that food scarcity and physical activity activate.” And, Patrick explained, the same goes for thermal stress.

According to Patrick, intermittent use of saunas mimics aerobic activity. She explained that many physiological responses to heat are similar to physical activity. For instance, they both increase heart rate. Patrick said heat exposure can increase heart rate to 120 beats per minute, as seen with moderate-intensity aerobic exercise.

In addition, a sauna session can increase cardiac output and cause blood to redistribute and go to the skin to help facilitate sweating, explained Patrick. Heat exposure also increases stroke volume and elevates core body temperature. “These are all things that happen when a person is deliberately exposing themselves to heat. But it also happens when a person is doing aerobic exercise,” Patrick said.

Research on the health benefits of saunas has mostly come out of Finland, where regular sauna use is common. According to Patrick, in one study, researchers found that Finnish men who use the sauna four to seven times per week had 46 percent less hypertension than those who used the sauna once per week. Patrick also cited other studies that indicated frequent sauna use lowers blood pressure, improves arterial compliance, and increases heart rate variability.

To experience these health benefits, Patrick said duration, temperature, and frequency need to be considered. The finish parameters included over 19 minutes in the sauna at a temperature of 174 degrees Fahrenheit four to seven times a week for the most robust effects. However, the study also suggested that using the sauna two to three times a week can positively affect health.

According to Patrick, there are several methods for heat exposure. She said most studies on heat exposure have involved heat saunas. However, similar effects can be seen in other forms of heat exposure, such as infrared saunas, hot baths, and Waon therapy, a Japanese intervention that involves 15 minutes in an infrared sauna followed by 30 minutes in a warm blanket.

As for safety concerns, Patrick said sauna use is generally well tolerated by adults. However, children, those who recently experienced a heart attack, and elders prone to low blood pressure should avoid saunas or take extra caution before use. In addition, she warned never to mix alcohol with intermittent heat exposure.

Other health benefits associated with saunas include increased lifespan, a decreased risk of Alzheimer’s disease, lower stroke risk, and a reduction in depressive symptoms, according to Patrick.

In her presentation, Patrick also discussed the benefits of intermittent cold exposure. She explained that cold stress has been shown to improve mood and increase mitochondrial biogenesis in adipose tissues and skeletal muscle.

To achieve increased mitochondrial biogenesis, Patrick said one must sit in a 50-degree Fahrenheit setting for 15 minutes. Mood improvement after cold exposure is accomplished through an increase in norepinephrine, which Patrick said requires two minutes in a 50-degree Fahrenheit setting or 20 seconds at a temperature of 35 degrees Fahrenheit.

Although intermittent exposure to intense cold or heat has several health benefits, Patrick acknowledged that they are not particularly comfortable interventions. For patients who are sensitive to heat, Patrick said to start slow.

Acclimation does happen,” said Patrick. “Five minutes [in a sauna] is a good start for people who don’t handle heat well. Then, next time they stay in seven minutes, then ten minutes, and eventually the regulatory response starts to shift, and they’ll start to cool down quicker.”


Editor's note: This article is part of our live coverage of the 2023 Institute for Functional Medicine Annual International Conference. Click here for a list of full coverage.