Ice Bath for Female Fertility

Mitochondria are critical to conception

At the age of 41, Sarah Kleiner was determined to have a second child, but she lost two pregnancies and IVF failed to produce viable embryos. Four months after starting a regular practice of cold water immersion therapy, she conceived. At the age of 43 she gave birth to a healthy baby boy.

Summary

• Sarah Kleiner lost two pregnancies, failed at two attempts at IVF, but conceived naturally after starting a regular practice of cold water immersion therapy. She gave birth to a health baby boy at age 43.

• Mitochondrial health is critical to female fertility. Therapies that target mitochondria can boost fertility -- even for women in their 40's.

• Cold therapy is the best way to stimulate the production of new mitochondria and boost insulin sensitivity.

• Mitochondrial health is also essential to brain development, while Vitamin D is essential to development of the infant immune system.

Cold Is A Hormetic Boost to Female Fertility

When I first wrote about the advantages of Cold Plunge During Pregnancy I got a lot of unfounded criticism that sounded mostly like "Are you craaaazy?"

Pregnant women are correctly considered one of the most protected class of individuals, and the prevailing wisdom is that they should not be subjected to stressful environments. What most people don't realize is that pregnant women are already being injured by two common aspects of modern, technological life:

1. The Standard American Diet (SAD) full of processed carbs and artificial seed oils, and

2. Artificial lights and non-native electro-magnetic frequencies (nnEMFs),

3. Exposure to environmental toxins, including aluminum, fluoride, halogenated hydrocarbons (PFAS, BFR), air pollution, microplastics, and gut disruptors like glyphosate and mold.

   
   

In other words, people living under circumstances we now consider normal in America are already suffering from impaired mitochondrial function resulting from ultra-processed diets, poor light/EMF environments, and chronic toxic exposures. As I wrote in Why Is Testosterone So Low? the consequences for sexual and reproductive function can be devastating. In men, it can mean low libido, low sex function or erectile dysfunction, and poor sperm count. In women, it's even worse As a consequence of mitochondrial damage, the probability of pregnancy for the typical American woman declines precipitously after around age 30. That's when the accumulation of insults to the mitochondria begin showing up as degraded mitochondrial function.

The decline in female fertility with age is typically attributed to fewer, or lower quality eggs (oocytes) and explained as if that decline were an inevitable consequence of aging. In fact, it is an indication of declining mitochondrial function, and it can be restored.

To maintain mitochondrial health for fertility, pregnant women need to stay connected to the natural, hormetic stressors available in Nature more than anyone. They need nourishing food rich in protein and omega-3 fatty acids (like DHA). They need sunshine and the green light of the shady forest. They need long walks and light exercise to keep their muscles limber. They need to minimize exposure to aluminum, fluoride, glyphosate, pesticides, and heavy metals like lead and mercury, and they need brief, regular periods of deliberate cold exposure to keep their metabolism strong.

Ancient Chinese Cold

One of the objections to cold therapy that appears online sounds like "Traditional Chinese Medicine (TCM) says that the womb should be warm to support conception." These Instagram and Twitter posts are good examples in which women from Western, industrialized countries describe the ancient Chinese fertility wisdom somehow passed down to them from through the ages.

The problem with TCM is that most of my readers are not traditional Chinese women. They don't work hours in flooded rice patties, exposed all day to the weather. One account of traditional Chinese cultures says that women in agricultural regions were typically expected to work alongside men in the fields, doing hard physical labor (Wang & Ang 2025). For those women, a "warm womb" to promote conception may have been a necessary respite from the strain of overwork and undernutrition that will undermine female fecundity.

Chronic cold exposure, like chronic overexercise and chronic fasting, will destroy female fertility. I wrote about the dangers of undernutrition and overexercise for fertility in my Uncommon Cold book and a little bit more in Treat Anorexia With Ketosis. The basic principle is that overworked mitochondria have little excess capacity for fertility. For example, undereating and overexercising is why so many ballerinas experience amenorrhea (absence of menstrual periods, Lehbil et al. 2025). Chronic cold exposure can have a similar effect by placing mitochondria under constant stress without time for recovery.

Morozko is not recommending the chronic cold stress and hard manual labor of a traditional Chinese lifestyle for women seeking to conceive. Rather, readers keep sending us descriptions of their experiences with brief (3-5 minutes), acute cold water immersion therapy. For example, we recently heard from Sarah Kleiner, who lost two pregnancies at the age of 41, failed to produce viable embryos in two rounds of IVF at 42, and gave birth to a healthy baby boy, conceived naturally, at the age of 43.

For Kleiner, it took only four months of regular ice baths to successfully conceive her baby. In fact, she says it might have happened even sooner, had she used shorter exposures when she first started her practice.

The Problem With Some Chinese Research

There are some Chinese studies that might suggest cold water immersion comes with a penalty for female fertility. For example, researchers in China exposed female rats to acute cold water immersion at 4C for just six minutes a day, and compared physiological markers to control mice that were kept warm and dry. That sounds like exactly the type of experimental protocol that Morozko would expect to boost metabolism and mitochondrial function.

It did not.

Female mice subjected to six minutes of 4C cold water immersion followed by toweling and blow drying exhibited increased body mass and reduced markers of fertility (Sun et al. 2025).

The experimental mice subjected to cold exhibited increased body mass due to greater subcutaneous fat, and massive changes in sex hormones that are associated with reproductive function. Researchers measured increased follicle stimulating hormone (FSH), increased luteinizing hormone (LH), increased anti-Müllerian hormone (AMH), and increased estradiol (E2). They did not measure testosterone, nor fertility. However, the study authors speculate that "Cold environment exposure may induce inflammatory responses in the uterus and ovaries, contributing to the formation of an inflammatory microenvironment in the reproductive system. This process may lead to disruptions in sex hormone levels and ultimately impair female reproductive capacity" (Sun et al. 2025).

I doubt their interpretation.

Massive changes in sex hormones related to reproduction function were observed in mice subjected to cold water immersion, toweling, and blow-drying (Sun et al. 2025).

FSH and LH can be associated with impaired reproductive function in women. As signaling molecules, these hormones indicate the strength of the communication from the pituitary to the ovaries. High levels of FSH and LH do not necessarily indicate low ovarian function, but they do indicate that the pituitary is pumping out more hormone to create a stronger signal.

Increased AMH is typically associated with health ovarian function and is associated with higher rates of successful pregnancy. The elevated estradiol is a difficult result to interpret. The results in the cold-exposed mice are similar to those measure in human case studies of women practicing cold water immersion therapy, and could result from increased mitochondrial function. Absent related indicators of morbidity, high estradiol could be interpreted as a positive indication of fertility.

I wrote about the many hormonal benefits of ice baths in Ice Bath Benefits Women, so when I first saw the conclusions in this paper, I knew I would have to re-examine my views -- especially since other mouse studies have shown a big boost in fertility, and resolution of polycystic ovarian syndrome, in mice from deliberate cold exposure (Ye et al. 2021). What I realize now is that the Chinese mouse data looks trustworthy, but the interpretation of that data does not. Nonetheless, the markers of increased inflammation are troubling. Ice bath is known to reduce inflammation, so how could it be that these researchers observed increases, compared to controls?

When I read more closely, I discovered that the experimental mice weren't just exposed to cold water. The method employed was:

Cold exposure was simulated by immersing the mice in cold water (4°C) daily at 15:00, with the water level reaching the neck while ensuring unobstructed breathing. Each immersion lasted for 6 minutes. After exposure, the mice were immediately removed from the water, dried with a towel, and dried with a hair dryer to prevent hypothermia-induced mortality. The procedure was repeated for 21 consecutive days, and body weight was recorded every 3 days. - Sun et al. (2025, emphasis added)

In other words, these mice were subjected to 21 straight days of acute cold water immersion, towel-handling, and immobilization while being blown with hot air. Then they were euthanized and dissected.

I'm surprised that the researchers thought just 6 minutes of swimming in 4C water might create a risk of hyperthermia-induced mortality in mice, because it doesn't. Nevertheless, the proper way to conduct this study would have been to subject the control mice to the same rough treatment, albeit with warm water. That is, the control group should have been immersed in water, toweled off, and blown dry, just like the experimental.

They were not.

I suspect that the hormonal markers in the study could be considered consistent with robust fertility, which the researchers never measured directly, and that the body weight and inflammation markers might be due to the torture of rough handling in the experimental group. We'll never know for sure.

This detailed analysis of the study method exemplifies how some scientists (and their readers) can draw unreliable conclusions that reinforce pre-existing biases, rather than work to falsify hypotheses.

Healthy Metabolism for Healthy Pregnancy

While I've previously explained the benefits of cold water immersion therapy during pregnancy in Cold Plunge During Pregnancy and Ice Bath Eases Pregnancy, there are two additional points that I should explain: 1) Vitamin D, and 2) omega-3 fatty acids.

Vitamin D for Immuno- and Neurodevelopment

Kleiner did something unusual during her pregnancy that helped her baby son develop a healthy immune system: sunbathing. As I wrote in Re-ordering Autoimmune Disorders, all autoimmune disorders, including my son's Type 1 diabetes, originate in aberrant Vitamin D metabolism.

A human infant is born without a mature immune system. It develops rapidly only after birth, and Vitamin D is indispensable for the healthy maturation of that immune system. Vitamin D deficiencies in the Mother (on whom the baby relies for antibodies via breastmilk) or the infant are associated with later diagnoses of Type 1 diabetes, multiple sclerosis, Parkinson's, and other autoimmune malfunctions. However, the time that Kleiner spent out in the sunshine ensured that both she and her baby would have all the Vitamin D they needed for his immune system to develop along a healthy trajectory (e.g., Mehta 2010).

What she could not have known at the time is that deliberate cold exposure is also a source of Vitamin D. This fact surprises most people, although I explained the mechanism in Cold Thermogenesis Makes Vitamin D from Biophotons. The beauty of the human body is that when sunshine is not available during the winter, cold activation of brown fat makes UVB light inside the fat cell, where this light converts cholesterol into previtamin D -- which gives pregnant women another reason to practice brief cold water immersion therapy in their late pregnancy.

Brain Development Relies on Fat

It was University of Sherbrooke Professor Steven Cunnane who alerted me to the fact that the brain is built from omega-3 fatty acids like DHA and omega-6 fatty acids like ARA obtained from animal sources. Almost two-third of the brain (by weight) is composed of fat. While many nutritionists correctly recommend a high protein diet for pregnant women, few acknowledge the critical role of dietary fat, and omega-3 fatty acids from fish in particular.

Fats are critical for healthy development of the human brain. In this clip from the Uncommon Living podcast, University of Sherbrooke Professor Steven Cunnane explains that the omega-3 fatty acids found in fish oils were once recognized as "Vitamin F," but the term has since fallen into disuse.

The salmon roe that Kleiner included in her diet, which is rich in DHA and other omega-3 fatty acids, supported the healthy development of her son's brain and central nervous system. She reported that at age 3, her son still snacks on salmon roe, because it was one of the first solid foods on which she started him when it came time to wean him from her breast.

References

• Mehta BK. New hypotheses on sunlight and the geographic variability of multiple sclerosis prevalence. Journal of the neurological sciences. 2010 May 15;292(1-2):5-10.

• Lehbil S, Couillandre A, Dreyfus M, Ibargüen-Vargas Y, Kern L, Barreau X, Maître C. Menstrual cycle disorders among elite ballet dancers. Science & Sports. 2025 May 1;40(3):256-65.

• Sun H, Zhao Q, Liang X, He Y, Li Y, Yu J, Ding J, Yu C. Effects of cold environment exposure on female reproductive health and its regulatory mechanisms. Frontiers in Genetics. 2025 Apr 9;16:1570053.

• Wang J, Ang JB. Cultivating equality: The effect of traditional farming practices on gender disparity in China. China Economic Review. 2025 Oct 1;93:102455.

• Ye R, Yan C, Zhou H, Huang Y, Dong M, Zhang H, Jiang X, Yuan S, Chen L, Jiang R, Cheng Z. Brown adipose tissue activation by cold treatment ameliorates polycystic ovary syndrome in rat. Frontiers in Endocrinology. 2021 Oct 14;12:744628.

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About the Author  

Thomas P Seager, PhD is an Associate Professor in the School of Sustainable Engineering at Arizona State University. Seager co-founded the Morozko Forge ice bath company and is an expert in the use of ice baths for building metabolic and psychological resilience.

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