As one form of hydrotherapy, the health benefits of cold water therapy are numerous.  Cold showers provide a gentle form of stress that leads to thermogenesis (internal generation of body heat), turning on the body’s adaptive repair systems to strengthen immunity, enhance pain and stress tolerance, and ward off depression, overcome chronic fatigue syndrome, stop hair loss, and stimulate anti-tumor responses.

Some people advocate starting with a warm shower, and switching over to cool or cold water only at the end of the shower. This is fine, particularly if you are afraid that a pure cold shower would just be too uncomfortable or intolerable.  But I prefer just jumping right in. When you start with cold water, you will experience the phenomenon of cold shock, an involuntary response characterized by a sudden rapid breathing and increased heart rate. This in itself is very beneficial. The extent of cold shock has been shown to decrease with habituation, and exposure to colder water (10C or 50F) appears to be more effective than just cool water (15 C or 59F) in promoting habituation. The habituation itself is what is most beneficial, both objectively and subjectively. There is an analogy here with high intensity resistance exercise and interval training, both of which elevate heart rate and lead to long term adaptations to stress, with improved cardiovascular capacity and athletic performance.

But cold showers provide a different and probably complementary type of habituation to that which results from exercise. A study of winter swimmers compared them with a control group in their physiological response to being immersed in cold water:  Both groups responded to cold water by thermogenesis (internal production of body heat), but the winter swimmers did so by raising their core temperature and did not shiver until much later than the controls, whereas the control subjects responded by shivering to increase their peripheral temperatures. The winter swimmers also tolerated much larger temperature differences and conserved their energy better. Other studies confirm that the benefits of habituation show up only after several weeks of cold showering. For example, adaptation to cold leads to increased output of the beneficial “short term stress” hormones adrenaline and thyroxine, leading to mobilization of fatty acids, and substantial fat loss over a 1-2 week period.

So regular cold showers, like high intensity exercise, and intermittent fasting, appear to provide similar, but not identical hormetic benefits.

But now I’d like to focus on the subjective experience of taking cold showers, something not commented on in many of the studies I’ve read. If you follow my approach and plunge right into a cold shower, you’ll get the initial “cold shock” mentioned above:  a quickened pace of breathing and a pumping heart.  Often I find myself involuntarily smiling or even laughing.  For waking up, this beats caffeine. I keep the water cold the whole time. It helps to brace yourself when entering by gritting your teeth and stiffening your muscles. Go in head first and alternate from back to front to make sure you are getting cold all over, including your hands and arms and any sensitive zones. After about a minute, you’ll find the cold water starts to become more tolerable, and after 2 or 3 minutes you’ll feel your body getting warm by its own efforts. This is thermogenesis. I make a point of staying in the shower until I’m no longer uncomfortable.  I found that at first my hands were the most sensitive part, and now they are no longer as sensitive, so they have habituated.

When I started taking cold showers, I measured the water temperature at around 60 F (16 C), but over time I have reduced this somewhat to 50-55 F (10-13C) as my body has adapted. (You can determine this by bringing into the shower a plastic cup and meat or candy thermometer and collecting some water once the temperature equilibrates).  Of course, depending on where you live and the season, there is a lower limit to how cold you can go, but in general you should be able to get at least as cold as 60F in most places. Also, my cold showers used to be very short, maybe 4 or 5 minutes, but now they last as long as my previous warm showers, perhaps 10 minutes.  I still take the occasional warm shower, perhaps once every week or so, but I prefer the cold ones.

I find that cold showers are great for the mood.  Not only are they physically invigorating, they make you feel alive, vital and ready to take on the day. They stimulate thinking early in the morning. I also believe that they have the effect of slightly raising blood glucose very quickly — by perhaps 10 mg/dl, and thereby have an appetite suppressing effect. Generally, this rise in blood glucose is relatively short in duration, but that’s good enough to prime the pump and get the day started.  This effect of cold showers works well with my practice of skipping breakfast most days and often fasting until dinner.

These effects are apparent with the first cold shower. If you continue the practice for several weeks, you’ll find the psychological benefits are even greater. First and foremost, cold showers appear to have improved my stress tolerance, by buffering emotional reactions. What I mean by this is that bad news, surprises, arguments, or events that would have previously caused a brief surge in adrenaline or an emotional flush, no longer have that effect, or at most have a very attenuated effect.  I think this is a consequence of becoming acclimated to the the adrenaline-producing effect of the cold shock.  A deeper explanation of why cold showers are effective in boosting mood, and why the psychological benefits of cold showers increase the longer and more frequently you take them is addressed in my recent post on the opponent-process theory of emotions.

As with any application of Hormetism, you can experiment with the intensity of cold, the duration, and the frequency of cold showers to improve your tolerance at a tolerable rate.  If you find that your heart is beating uncomfortably fast or you are going numb or experiencing pain of any sort, that’s a good reason to ease into the routine more slowly with water that is not so cold. Check with your doctor first if you have a heart condition, migraines, or pain.  But don’t sell yourself short and rush through a cold shower, because you may find that extending a few more minutes provides the greatest benefits in adapting your body to tolerate stress. Not just cold stress — but physical and emotional stress in general.

January 29, 2012 update:  If you want to take cold showers to the next level, check out this recent article on The Iceman.

Biological markers. After these ordeals, Dr. Andy Morgan of Yale Medical School found that the top performers had very different physiological responses from those who couldn’t hack it. He did extensive physiological monitoring and found that those who passed these tough tests had much higher levels of NPY (a neuropeptide) and DHEA (a hormone that buffers the effects of cortisol, a stress hormone).  In addition, those who did best also had “metronomic heartbeats” — very little heart rate variability (HRV), compared to most normal people, who show a lot of variability in the intervals between heartbeats.

These biological markers of stress-resistant individuals show that they are somehow different than most of us.  Perhaps this is worth looking for what it can teach the rest of us.   Certainly, there are other health known health benefits that have been reported for NPY and DHEA.

Autonomic nervous system. Regarding HRV, however, Sherwood raises a caveat, noting that numerous studies have associated metronomic heartbeats (low HRV) with cardiovascular disease, diabetes, and even sudden death.  However, other research into the HRV paints a more complex picture.  A paper on the Intellewave Method,  by Dr. Alexander Riftine,  indicates that low HRV may have different implications for the state of the autonomic nervous system, depending on the frequency of the heartbeat variability, derived from heart rhythmograms.  When spectral analysis (a mathematical technique based upon Fourier Transforms) is applied to the heart rhythmograms, the heartbeat frequency variations are resolved into high frequency (HF) and low frequency (LF) patterns.  The LF variations are associated with the sympathetic nervous system (SNS), where as high frequency HF variation correlate with the parasympathetic nerous system (PSNS).  The balance between SNS and PSNS states predicts much about an individual’s fitness.  According to Dr. Riftine, these states cluster into nine typical combinations.  The ninth state–an elevated PSNS with a reduced SNS state–is “rather unusual because normally an increase in PSNS is accompanied by an increase in SNS.  This rare condition is found in water polo athletes, long-distance runners, navy seals and persons with special heart training for deep sea diving.”

The physiological analysis of individuals who have successfully adapted to tolerate stress is a promising area ripe with lessons for the rest of us, as it could be used to assess, predict, and track our progress in getting stronger and more stress-hardy.

Tennis. Loehr gleaned some of his most perceptive insights by using telemetry to observe the behaviors that separated the top tennis players from the lower ranks. Specifically, he found that the best tennis players are intense and focused during play, but show a remarkable ability to recover during “between-point” time, following routines that allowed them to pause and recover their energy for the next point. During these brief periods–approximately 25 seconds–between points, “top competitors were much more skillful oscillators during competition. The rhythmic increases in heart rate during points, and decreases in heart rate between points, meant that a competitor was adapting to the stress.” (SFS, p. 167). By contrast, poor competitors did not use their downtime wisely, not relaxing or even exacerbating the stress by disputing calls or showing emotion.

Toughening. The best of Loehr’s ideas are encapsulated in Part III of “Stress for Success”, entitled “Life Skills and the Toughening Process: Targeting Stress Exposure”. This section presents what I believe are the key concepts for effective toughness training based upon deliberate and controlled exposure to stress. Loehr takes research from sport science and applies it to training for toughness in everyday life.  ”For decades, sport science researchers have been diligently investigating the relationships between stress and growth.  The optimal frequency, duration, and intensity of stress exposure for improving strength, speed agility, endurance, stamina, and toughness of all kinds have been vigorously pursued. The most important confirmation in all the research is simple and direct:  STRESS IS THE STIMULUS FOR ALL GROWTH.”  (SFS, P. 145).

Oscillation. Loehr goes on to describe training routines whereby one can increase stress tolerance by deliberately using intermittent intervals of stress exposure, oscillating with periods of recovery and rest. One of the most effect means of doing this is excercise, specifically interval training. According to Loehr, “exercise is really stress practice,” and he cites the training principle of “specificity” to argue that the exercise stress should oscillate, so that they resemble the up-and-down of stresses in real life. The intermittent stresses should be intense to the point of discomfort, but never painful. And the use of intervening periods of “active rest” and sleep are equally important for recharging.

The benefits of this approach to oscillatory stress training have biochemical correlates. Loehr cites research indicating that, whereas chronic, sustained stress leads to depletion of the stress hormone norepinephrine and elevation of cortisol, intermittent acute stress, followed by recovery, allows for increased tolerance and resistance to norepinephrine depletion.

Although Loehr mentions that sports scientists have studied the optimum intensity, duration, and frequency of applied stresses in exercise, he does not provide in his book any specific guidelines for optimizing these variables, beyond noting that they will vary based on the nature of the stress and subjective factors such as discomfort and pain thresholds. While being aware of one’s own thresholds is no doubt good advice, it seems to me that turning exploring the quantitative aspects of this science would be useful in helping to reveal more objective factors.

Beyond exercise. I believe that the application of stress and recovery cycles for training can be generalized beyond the use of physical exercise. Following the principle of specificity, why not train for life using more  specific stresses encountered in life, specific distractions or irritants, including physical stresses such noise, heat, or hunger; or interpersonal irritants such as yelling, nagging, or insulting. In fact, such deliberate exposure to stress and hardship is a techniques going back to the Stoics, who recommended training oneself to tolerate increasing levels of physical stress and discomfort by means of cold baths, sleeping on the floor, fasting, and learning to tolerate insults. Extreme forms of such exposures to stress have been used by the Army and Navy to harden their special forces (See my previous post on The Physiology of Stress), but I believe there is a lot of opportunity for both creativity and the use of proven behavioral science in developing and optimizing specific and effective techniques to help us become more resistant to a variety of life’s everyday stresses.