How does swimming in cold water affect your health?

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Q: I keep hearing about the benefits of swimming in cold water. Is it actually good for you?

A: There is intriguing preliminary evidence that swimming in cold water may have antidepressant effects.

One study, conducted in Britain in 2020, reported that swimming in the cold ocean reduced depressed mood up to 10 times as much as it did in a group of controls who watched the swimmers from the beach. And a separate case report found that a woman with treatment-resistant depression experienced significant improvement in her depressive symptoms after swimming in cold seawater once a week.

But studies about the mental health benefits of cold water swimming tend to involve swimming with other people, so it’s hard to know whether it’s the socializing with others — or the swimming itself — that provides most of the observed antidepressant effect.

Still, cold water exposure has arousing and stimulating effects, and it appears to increase many substances that we know are involved in regulating mood. For example, studies that immerse healthy subjects in cold water show a spike in the stress hormones cortisol and norepinephrine. This is the same response that humans and animals have to danger and threat, and it is part of our hard-wired flight or fight reflex that affords enormous survival advantage.

Also, exposure to cold water causes release of endorphin and dopamine, which are neurotransmitters that convey a sense of pleasure.

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I’m familiar with this feeling. On a recent hot night, I ran off to a large outdoor pool in Manhattan that was full of delightfully cool water. It was initially stimulating, but soon after I starting swimming, I was overtaken by a feeling of tranquil euphoria probably brought about, in part, by an endorphin rush in my brain.

And just this past weekend, I swam in a 1.3-mile open-water race in Provincetown, Mass., with my husband. I’ve done it 23 times before — that’s how great the experience is. It’s challenging in unpredictable ways each time, but one thing is constant: The rapture of swimming in cool water.

As a psychiatrist and avid swimmer, I’ve probably prescribed more exercise than antidepressants over the years. And since swimming is such a wonderful form of aerobic exercise that’s easy on the joints, I often encourage my patients to try it. And if you don’t live near a lake or ocean or have access to a swimming pool, a cool shower can have similar effects.

How cold does the water need to be?

The good news is that you don’t have to risk a polar plunge to reap the potential benefits of cold water. Cold water is typically defined as water below 60 degrees, which is very cold indeed. But we know that cool water, say around 70 degrees, can effectively trigger the “diving reflex” and increase parasympathetic activity, which is calming.

Furthermore, exposure to just modestly chilly water, between 60 and 70 degrees, has been shown to boost dopamine and endorphin levels. You can easily achieve this in your shower at home, by gradually turning down the hot water and slowly habituating yourself to cooler water over a week or so.

There is even preliminary evidence that adapting to progressively cooler showers has antidepressant effects. It might also, like cold immersion, promote something we call cross-adaptation and make you less stressed in response to other adverse situations. For example, one study of healthy young men who had been habituated to cold water showed lower stress responses to exercising in a low-oxygen situation, which is unpleasant and hard, than those who had not been previously exposed to cold water.

What are the risks of swimming in cold water?

Contrary to what you may have heard from cold water enthusiasts, cold water plunges are definitely not for everyone and they are not without risk. One major reason is that cold water exposure activates both components of our autonomic nervous system, which have opposing effects.

How you enter the water matters. If you enter the water without getting your face wet, it triggers the sympathetic system, which increases heart rate and blood pressure, sometimes dramatically. In contrast, when cold water hits your face, you get the diving reflex, which activates the parasympathetic system via the vagus nerve, which lowers heart rate and slows things down.

The net effect of these two competing neural reflexes is highly variable. In some individuals with known or perhaps covert heart disease, it can trigger a potentially fatal cardiac arrhythmia — even in apparently young healthy people.

Some people respond immediately to cold water immersion with cold shock, which involves uncontrollable hyperventilation, fatigue, disorientation and can end in drowning. Of course, there is also the risk of hypothermia with prolonged exposure to cold water, so people should be mindful of these potential risks before plunging into frigid water.

The notion that cold water has healing properties is quite old. In 400 B.C., Hippocrates recommended cold water therapy to allay lassitude. More recently there’s been a lot of enthusiasm about the supposed physical and mental health benefits of cold water immersion. Many of the claims — that a frigid plunge can help you say goodbye to depression, chronic pain of all sorts and turn the clock back on aging — are unproven and well ahead of the science.

But as scorching heat becomes more common — with some parts of the country enduring it year-round — there’s another compelling reason to head for the water: It’s not only a powerful way to boost mood, energy and cognitive function, it’s a refreshing and fast way to cool off.

Richard A. Friedman MD is a professor of clinical psychiatry and director of the Psychopharmacology Clinic at Weill Cornell Medical College. Trisha Pasricha, MD, MPH, will return next week.

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