The Truth of Chilling: Heart risks and benefits of cold water exposure

Introduction

In clinic last week, a patient asked whether they could begin cold water swimming following their bout of a particular heart problem. Whilst they were feeling back to normal, and had started indoor swimming again, I had no idea what the real, evidence-based risks were to answer their question. This type of activity fell under the category of “healthy stressors” and I was unclear exactly how “healthy” it could be, but I also wanted to be certain I was giving my patient the right advice so they could make an informed choice. They were, after all, doing the right thing by consulting me, but I had to do research to discover more.

Of course, denying them the opportunity to take up a potentially beneficial past-time seemed wrong, but at the same time, I did not want to tell them, “All would be well," when it might end in catastrophe!

What are the possible benefits of cold water exposure?

These are far from decided; the evidence is by no means large in volume, is inconsistent in its methods, and it is far from clear what the optimum regime might be to achieve the most gains for any one individual. Separate studies noted gains from temperatures as mild as 17 degrees C (63F) and as little time as 15 minutes. These levels seem to vary across different studies, and there seems to be no consensus (or comparative analysis) that would allow us to see the differences in a single person (let alone a sample) after adjusting either the temperature of the water and/or the duration. While we can see adjustments across the studies, the data seems too independent to make a true assessment of its value because we cannot know if the results are due to either the particular experimental conditions or the participants themselves. For example, it is perfectly possible that the time of day and how well the participant slept the night before both play a huge role in whether or not we see a reduction in inflammation the next day. Or it may have no impact at all. While it may be costly and/or more difficult to control for these factors, they could be vital to helping us as clinicians decide the conditional probability of any particular patient’s risk.

What can be observed from both animal and small human trails:

Improved Blood Flow: Initial constriction followed by dilation of blood vessels may enhance circulation.
Reduced Inflammation: Adaptation to cold water may reduce inflammation, benefiting cardiovascular health.
Activation of the Immune System: Cold exposure can trigger immune responses, indirectly supporting cardiovascular health.
Stress Reduction: Improved mood and reduced stress levels from cold plunges may positively affect cardiovascular health.

What are the potential risks of cold water exposure?

The list of risks is sadly longer than the list of benefits. That does not mean they necessarily outweigh the benefits in your circumstances. It would be important to consult with a physician who knows you well and can help you decide whether it is safe for you and how to do it best in your situation.

The reasons why things might go wrong are largely related to how the body works in response to the cold temperature

Cold Shock Response: Sudden immersion in cold water can cause a rapid increase in breathing rate, heart rate, and blood pressure, putting additional stress on the cardiovascular system. Prolonged exposure to cold water can lead to hypothermia, further stressing the cardiovascular system.
Increased Risk of Abnormal Heart Rhythms (Arrhythmias): The release of stress hormones like adrenaline, noradrenaline and cortisol during cold water exposure can disturb heart rhythm, posing a risk for those prone to arrhythmias.
Exacerbation of Existing Conditions: Individuals with pre-existing heart conditions may experience worsening symptoms due to the cardiovascular stress induced by cold water.
Blood Pressure Changes: Cold water causes blood vessels to constrict in the arms and legs, forcing blood back to the middle of the body and increasing blood pressure. For those with high blood pressure, or those with condition that require avoidance of rapid blood pressure changes (previous heart attack or aortic problems), it would be best avoided
Diving Reflex: Immersing the face in cold water can cause significant drop in heart rate and increase the blood pressure even further

A Note on Atrial Fibrillation

Cold water exposure can trigger atrial fibrillation (AFib) in individuals with a history of the condition previously, or any faster heart rhythms in the past.

Autonomic Conflict: Cold water immersion activates conflicting reflexes in both fight/flight and rest/relax systems. This tension can lead to arrhythmias.
Increased Risk for AFib: Cold exposure is a known trigger for AFib specifically, with anecdotal evidence from case studies, even in previously healthy individuals without any previous cardiovascular risks, or predisposition for AF.

Is swimming safe for those with heart conditions?

The British Heart Foundation have excellent resources here. It is really important to get bespoke advice that fits you. General guidance on swimming safely with heart issues includes:

Water Temperature: Swimming in water between 26-33°C (79-91°F) is recommended for those with heart conditions.
Gradual Acclimation: Enter and exit the water gently to adapt to temperature changes.
Exercise Intensity: Exercise at a lower intensity in water due to the increased cardiovascular workload.
Avoiding Isolation: Swim with a friend or group for safety and social benefits.
Medical Consultation: Always consult with healthcare providers before engaging in cold water activities.

Conclusion

The evidence base is lacking in both reassurance of safety and potential benefit for cold exposure, cold water swimming, and plunges for those with pre-existing heart conditions. Additionally, the specific person, may or may not benefit at all in any way from cold water exposure, and possibly the risks in these cases could outweigh the benefits. There are too many other factors that govern circulation, inflammation, the immune system, and stress levels for us to say definitively that cold plunges yield any greater health benefits than good sleep, regular exercise, and a balanced, whole food diet.

Of course, it’s a good idea to be aware of our bodies and how we might improve our overall health. Above all, it’s important to enjoy ourselves and take part in activities that make us feel good. So, provided there’s no harm in doing these activities, seek out these additional, incremental benefits, especially if the person finds them invigorating and/or feels empowered for having done them!

From my research, it would seem the conclusion in this case anyway is that cold water swimming and plunges cannot be recommended for those with a pre-existing heart condition. Indoor swimming is safe at warmer temperatures and provides an excellent form of exercise, which we do know improves cardiovascular health massively.

It is always important that you do your own research and seek medical advice before making drastic changes to your lifestyle

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