Cold water swimming has surged in popularity, with some enthusiasts convinced it keeps winter illnesses at bay.
Immunologist professor Eleanor Riley tells BBC Radio 4’s Inside Health podcast that the post-swim “high” is real, but it’s driven by adrenaline and endorphins.
“If you take a blood sample before and after a cold swim, white blood cell levels do rise,” she explains. “But that’s because the body thinks an infection might be coming, so cells move into the bloodstream.
“Within hours the levels go back to normal so your body hasn’t created any more white blood cells.”
Professor Riley adds that part of the benefit of cold water swimming comes from building a social connection.
Feeling “brighter, more alert and more connected” has real physiological effects.
Professor John Tregoning, a vaccine immunologist, says the benefits are mostly indirect and much of what makes people feel healthier in winter may come down to stress.
“It reduces stress because you’re outdoors with nice people in nice places. But you could get the same from dancing, singing or going for a run.”
Being in nature can lower your blood pressure and stress hormones that can dampen immune responses.
GP Dr Margaret McCartney explains that moderate exercise does show evidence of reducing viral infections, but that could be any form of exercise, not just cold water swimming.
