The original edition was published in 2019 under the title “Hop i Havel”, the German translation was published by Piper Verlag in 2022. The book is divided into 13 chapters and there are some references at the end. The book contains many photos and illustrations of winter swimming in various countries. The pages with “cold facts” are particularly practical – short and crisp summaries of the chapters in bullet points. The book is visually very appealing, well structured and fun to read.
The author offers a good general introduction to the topic of winter swimming with a lot of knowledge from the latest research results and general background information. This makes the book particularly suitable for beginners, but also interesting for experienced winter swimmers who want to learn more about the physical effects and brown fat in particular. For both groups, the book is a tremendous motivational booster and can be picked up again and again if the willpower should weaken a little.
Susanne Søberg lives in Denmark, where winter swimming has a long tradition and the clubs have long waiting lists. Many physiological, psychological and social aspects explain the feeling of happiness that winter swimming brings. Susanne is a scientist at the University of Copenhagen and studies the physiological processes and changes that take place in the body in the short, medium and long term as a result of winter swimming. Many questions, such as whether winter swimming prolongs life or even carries risks, have not yet been answered scientifically – and this is where Susanne’s work comes in. One of her studies found that the reaction to the cold shock, as measured by respiration, blood pressure, heart rate and noradrenaline, is less severe in the second season after the summer. A so-called coldhabituation therefore takes place. In experienced winter swimmers, blood pressure remains constant or drops. The strengthening of willpower, which is particularly important when you start winter swimming, can probably also be transferred to other areas of life. Another advantage of the intense physical experience, especially in this day and age, is the state of being completely in the here and now .
There are many terms for immersion in cold water. Winter bathing is mainly used for immersion in cold water during the winter, while in very cold regions, where a hole has to be hewn in the frozen water before immersion, the term ice bathing is more appropriate.
The first chapters are particularly aimed at newcomers, explaining how best to get started with winter swimming: there is an interview with two first-timers before and after their first dip. The best time to start winter swimming is actually always now. Simply continuing to swim after the summer has advantages and disadvantages, as some people find the difference in temperature between the air and water in the fall too great. In winter, the air already cools the body down considerably and activates the skin’s cold receptors, which reduces the cold shock. The cold receptors activate the release of noradrenaline and endorphins in the brain. Blood vessels constrict. The temperature difference between air and water was measured in Copenhagen and is greatest in October, February, March and April. The water in February therefore feels colder than in December or January. Salt water also feels warmer than fresh water. Gradually entering the water is also more difficult than diving straight in. The cold then feels more even. To start with, it is easier to dive in later in the day than in the morning due to the higher body temperature.
When practiced, a cold shock reaction lasts only 20 seconds – a cardiovascular reaction triggered by the sympathetic nervous system, characterized by hyperventilation, rapid heartbeat and high blood pressure. Presumably, immersion activates the diving reflex and, by stimulating the so-called baroreceptors, activates the parasympathetic nervous system, which explains the feeling of calm that soon sets in – as does a low pulse rate. It is therefore interesting to note that these two opposing forces occur simultaneously during cold water immersion. The cold shock reduces blood flow to the brain by 30%. The stress reaction is based on the hormones adrenaline, noradrenaline and cortisol. This is followed by endorphins, dopamine and serotonin, which have a positive effect on well-being. These neurotransmitters are briefly introduced in the book in connection with winter bathing. Dopamine, for example, increases by 250% in blood plasma due to immersion at a water temperature of 14°C. The body wants to have these hormones, as they increase well-being and therefore activities that lead to a large release are carried out again and again. Addiction factor guaranteed! Within 2 minutes there is an increase in noradrenaline due to cold water immersion caused by the change in skin temperature. Longer baths are not necessary.
In a further chapter, habituation to the cold is explained scientifically. Exposure to cold improves heat production by activating brown adipose tissue through noradrenaline and muscle tremor. As soon as muscle tremor starts, you should get out of the water as this is the first sign of hypothermia. More muscle mass is an advantage for heat generation. It also helps to change your own attitude towards the cold. In other words, not to fear the cold, but to accept it and thus relax more. Breathing exercises also help you to stay calm and relaxed. Exhaling deeply before immersing yourself in cold water increases your lung capacity and prevents panic and hyperventilation. Overall, less attention is paid to breathing in the book.
Søberg’s research focuses on the health effects of winter bathing on brown adipose tissue, which contains mitochondria. Brown fat is beneficial because it increases fat burning, increases insulin sensitivity and reduces the risk of diseases such as type 2 diabetes and obesity. When brown fat is activated, the cell takes sugar and fat from the bloodstream to generate heat by burning energy. This thermogenesis takes place in the mitochondria.
Studies have shown the positive effects of cold water on arteriosclerosis, joint pain, muscle injuries, stress and exhaustion as well as low mood and depression. Together with the sense of community created by groups and winter swimming clubs, winter swimming increases the quality of life. Furthermore, the long-term effects of winter swimming still need to be researched, e.g. whether it delays the ageing process or can prevent inflammatory diseases. It is known that winter swimming inhibits inflammation. In her book, Søberg provides brief information on individual diseases such as diabetes or arteriosclerosis, which are positively influenced by winter swimming.
Finally, the health-promoting effects of saunas are described. Regular sauna use is associated with a lower risk of death from cardiovascular disease, dementia, psychosis and Alzheimer’s disease.
All in all, “Winter swimming – why cold water makes us happier and healthier” is a highly recommended book with a lot of documented specialist knowledge and a beautiful layout that makes you want to go winter swimming!
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