Dear Doctor: Our family visits a lake in the mountains every summer where the water almost never gets above 60 degrees. I dislike swimming in cold water, but my husband and dad insist that it’s good for you. It won’t get me into the water, but I just want to know — are they right?

Dear Reader: Some people find cold-water swimming invigorating. Others, like the groups who take part in those midwinter “polar bear plunges,” love an even icier challenge. And then there are those of us who prefer not to suffer for our swim.

Swimming in and of itself is great exercise. Your heart, lungs and muscles all get a workout. The buoyancy of the water is kind to weight-bearing joints, and the concentration, isolation and repetition of swimming laps can be meditative. And while there are plenty of theories about how and why spending time in cold water is good for you — it sure does feel fantastic once you get out — when it comes to scientific evidence, things get a bit trickier.

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Research into cold-water immersion tends to focus on its use as therapy for sports injuries. Some studies with individuals who do open-water ocean swimming cite a lower rate of respiratory illness, but that data is anecdotal. And while several studies have found an increase in white blood cells in individuals who take daily cold showers, whether the resulting boost in immune response translates into long-term better health remains an open question.

What’s more apparent are the potential dangers of swimming in cold water. Water conducts heat far more efficiently than air. By some estimates, you lose heat 25 times more quickly in water than in air. That’s why the body responds so differently to a walk in 60-degree weather and a swim in water at that same temperature. It’s also why, when you get into water that’s 60 degrees or colder, it causes a phenomenon known as “cold shock.”

In cold shock, the body releases adrenaline and stress hormones, which can make you either feel exhilarated or panicky. In response to the sudden cold, you lose control of your breath. Your lungs contract and you gasp and breathe irregularly, a response that can last for up to a minute. To protect the vital organs, blood vessels contract, which raises blood pressure. As the body redirects blood flow away from the periphery and to your core, coordination can become impaired.

Because of this, experienced cold-water swimmers warn against jumping into icy water. Instead, they recommend that you dash water on your face, chest and shoulders to “warn” your nervous system of what’s coming. Then wade in, steadily but slowly, until you’re fully submerged. Monitor your breathing and heartbeat and, if all is well, off you go.

It’s understandable that your dad and husband would want to make swimming an all-family affair. But whether to brave the chilly lake is a matter of personal preference.

If you — or they — have high blood pressure or any heart issues, don’t do it. And if you are going to go the cold-water route (for just a few minutes or so the body will acclimate), have fun.
Just don’t stay out too long. And never swim alone.

Eve Glazier, M.D., MBA, is an internist and assistant professor of medicine at UCLA Health. Elizabeth Ko, M.D., is an internist and primary care physician at UCLA Health.