Updated: Nov 5
New Scientist (17 September 2022) reports that "There is a strong physiological basis underpinning the many positive health effects of outdoor swimming. These benefits largely come from a reduction in excess inflammation through repeated immersion in cold water.
The cold water affects inflammation in 2 ways: first, baseline and peak levels of inflammation are both lowered by the repeated exposure; second, putting your face in cold water directly stimulates the vagus nerve, and thereby the parasympathetic nervous system, which results in further, short-term reduction in levels of inflammation.
Many of Western society's health challenges are linked to abnormally high levels of inflammation, including heart disease, high blood pressure, type 2 diabetes, arthritis, fibromyalgia and chronic pain. A significant proportion of cases of depression are associated with inflammation. Self-sustaining interventions are ideal public health measures. Even if you don't have access to open water office workers who had cold showers took fewer sick days.
The water temperature needed to feel positive health effects is under 20 C."