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Study: Winter swimming associated with increased risk of strokes

Swimming in cold water—a popular Finnish winter pastime—increases the risk of strokes, according to a long-term study by Chinese scientists. Researchers compared death rates of winter swimmers and a control group over a thirty year period.

Avanto höyryää, alumiinitikkaat johtavat järveen.
Ice swimming is a popular winter hobby in Finland. Image: Miika Rautiainen

Winter swimming has long been regarded as a healthy pastime in Finland, but a new study by Chinese researchers challenges that view. Studies over shorter periods have shown some health benefits to swimming in cold water, but up to now there has been little research on the longer-term effects.

"I’m not aware of any (other similar research) and that’s why this study is really interesting," said Professor Hannu Rintamäki of the Finnish Institute for Occupational Health. "This emphasises the ill-effects of cold, which are well-known. Longer-term exposure to cold brings these kinds of results, ie that heart and circulation becomes heavier in cold water."

The study followed nearly 900 members of a winter swimming club. The study assumed that as they were members of a club they engaged in winter swimming on a regular basis, and that they had no heart or circulation problems.

The results showed that the winter swimmers’ death rates from heart attacks and strokes were 10 percent higher than would be expected according to statistics from the general population.

High death rates

"This is a long-term study and the sample is large, as there were more than 900 people in it," said Rintamäki. "When the sample is that big this is a clear difference, so sure in that respect this research was well-conducted."

The study did not look at how long the Chinese swimmers stayed in the water. In Finland many swimmers only stay submerged for a few seconds at a time—longer periods are always harder for the body to deal with.

"For example Germans swim in zero degree water for five to ten minutes, and that type of exposure is very different to normal ice-hole swimming in Finland," said Rintamäki. "In my opinion this research won’t yet affect Finnish people’s ice-hole swimming practices. I think we should react in such a way that in Finland we develop some ice swimming research. It has hitherto been intermittent; we haven’t done any systematic ice swimming research. There should be some kind of longitudinal study on this."

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