cold. Yeah. For reasons I still don't understand, people have associated me or this podcast with deliberate cold exposure. I like deliberate cold exposure in the form of a cold shower or a cold plunge or an ice bath, mostly for the effects that occur afterward. Oh yeah. Yeah. And every time I do a post about deliberate cold exposure, I get asked, understandably so, how does it affect women differently than men?

I prefer heat for women. Everyone's a responder to the heat. You get better adaptations. So sauna? Yep. Sauna. Hot tub? Yep. Preferably a true finished sauna. Infrared doesn't, it warms the skin, but not the core. Thank you for saying that. I'm not a big fan of infrared sauna because it doesn't get hot enough.

No. Yeah. You can bring an infrared light into a traditional sauna if it can tolerate the heat. Yeah. So the thing with cold water exposure is the whole conversation about ice cold, ice baths and how cold it is. It's too cold for women because when we're looking at that severe immediate jump into that icy cold, it causes such severe constriction and shutdown.

So women do really well and get that whole dopamine response and everything. If the water is around 16 degrees C, which is 55 to 56 degrees Fahrenheit. Which is chilly. It's chilly. It's not warm. No. It's go dive in San Francisco Bay, right? And that is enough to offset that severe constriction survival, but it is cold enough to invoke all the changes that we want with cold water exposure.

So it's a temperature nuance that sets sex difference. And like I said, when I have open water swimmers who are going to do a long swim or they're going to do a triathlon and the water is colder, I have them do cold water exposure, especially face exposure into the cold water to get them habituated to that initial severe constriction and sympathetic activity that we don't want to happen before a race.

With heat being the true heat that we're talking about with sauna, we see a lot of metabolic changes for women. So we're having better insulin and glucose control. We're seeing a better expression of our heat shock proteins and the uncoupling and the rebuilding of those proteins that are cardiovascular responses.

And then for women as we get older and have the offshoot of hot flashes, night sweats, that kind of stuff. If you're doing heat exposure, you're sending a stronger stimulus to the hypothalamus and you're also getting a better serotonin production from the gut because we have 95% of our serotonin produced from the gut, which lends to better temperature control and shuts down hot flashes.

So it's not that you disapprove of using deliberate cold exposure. You just recommend that women do deliberate cold exposure with temperatures that are maybe in the low 50 degree Fahrenheit range as opposed to the really, frankly, just painfully cold for anybody, 38 to 50 degree temperatures. I've been asked whether or not pregnant women can do deliberate cold exposure probably no fewer than 2,500 times on social media.

And I never have an answer, but I always default to the cautious answer, which is, uh, please don't until you talk to somebody who actually has an answer. Yeah. Just because it sounds like a very precarious situation, but in all honesty, I don't know. I'm just biding time there and just saying, please go ask somebody who can give you a definitive answer.

Yeah. So we see women who have a high risk for miscarriage, that anything that they do that's incredibly stressful for the first 12 to 20 weeks will put them at a higher risk for it. So being very cautious, especially with cold, because we know that there are so many different nuances doing something like hot yoga when you're pregnant is not, there is research.

So it's not detrimental because, yeah, because when we're looking at blood flow diversion that way, when you have slight hypoxia to the placenta and to the baby, there is a rebound effect that increases the vascularization so that the baby has better nutrients. We see this also with like exercise and exercise intensities.

This is why people are now saying you need to have some kind of blood flow change and increase in core temperature to create these vascular effects effects within the placenta to improve nutrient and nutrient delivery to the developing fetus. So heat's good. Cold, I'm not so sure of. But probably not extreme heat.

Not extreme heat. So that's why I mean like hot yoga is not going to the sauna. Hot yoga sits around 40 degrees Celsius. So what is that? Just around 100 degrees Fahrenheit. And in that situation, if you're feeling too hot, you leave, you lie down on the floor, don't try to stay for the whole class.

But it's not going to be detrimental unless you're pushing yourself too much. Again, everything in moderation, especially when you're pregnant. It's almost the inverse of what we know for males, which is if men want to conceive, they should avoid the sauna because we know that heat is detrimental to sperm viability in a real way.

So much so that I tell guys, if they are trying to get their partner pregnant, that they should bring an ice pack into the sauna. They should insulate that ice pack. Don't put it directly on the scrotum for other reasons, but that it's a, you know, that the effects of heat, the negative effects of heat on sperm are real.

But there's also an interesting, it's not just a trend. There's actually some research showing that cooling the testicles leads to increases in testosterone, which is on the face of it kind of counterintuitive because it turns out that it's about the vasoconstriction causing the subsequent increase in blood flow, increased vasodilation.

So the inverse of what you just said, which is that during the heating process, the hypoxia induces more vascularization of the placenta. So when talking about temperature, one always has to think about the surface of the body versus the brain response, as we talked about earlier, and then what's happening during the deliberate heat or deliberate cold versus what's happening after the deliberate heat or deliberate cold, right?

Everything in biology is a process, not an event. Yeah. And I should make full disclosure. I started as an environmental exercise physiologist and my PhD was all in heat and heat research. So I'm a little bit biased towards heat, but I've done a significant amount of research in the hot and cold.

Thank you for the disclosure. Yeah. I see it more as an indication of real knowledge. So thank you. This is an aspect of your training I knew a little bit about based on your publications, but I didn't realize the depth of knowledge. So we're all benefiting here.