Repeated cold-water immersion modestly alters immune markers without establishing protection from illness.
Repeated cold-water immersion can modestly alter circulating immune markers, but whether those changes improve resistance to infection remains unknown. Researchers examined young athletic men exposed to water at 14°C (57.2°F) for one hour. They assessed both the response to a single immersion and adaptation to three immersions per week for six weeks.
A single immersion produced minimal immediate immune changes. After six weeks, researchers observed small but statistically significant increases in the proportions of monocytes and lymphocytes expressing the IL-2 receptor CD25, along with higher plasma tumor necrosis factor-alpha and several acute-phase proteins. Other T- and B-cell populations showed nonsignificant upward trends.
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Many measurements did not change significantly, including total leukocytes, granulocytes, neutrophils, immunoglobulins, complement proteins, C-reactive protein, and several other inflammatory markers. The study did not measure common colds, influenza, or any other clinical infection outcome.
The investigators concluded that repeated cold stress activated the immune system to a slight extent but that the biological significance remained unresolved. The protocol - one hour in 14°C water - is also far more intense than a brief cold shower and should not be used to infer an optimal consumer cold-exposure routine.