The link is an interview with the study author, and excerpts are below.

This is the first high-level evidence showing that cold showers can benefit your health. People who took them for at least 30 seconds for one month called in sick 29% less than our control group — and 54% less if they also engaged in regular physical exercise.

Participants who took the cold showers actually reported feeling ill just as many days, on average, as the people who showered normally. But either their symptoms were less severe or they felt more energetic, so they were better able to push through the sickness and function anyway. The exact effect on the immune system is unclear, but we do have some knowledge of the pathway through which it works. Cold temperatures make you shiver — an autonomous response to keep your body temperature up. It involves a neuroendocrine effect and triggers our fight-or-flight response, causing hormones like cortisol to increase, shortly before we shift to a relaxation response. Moreover, cold temperatures activate the brown — or good — fat in the body.

Brown fat doesn’t have any proven connection to immunity, but it does affect the body’s thermoregulation. When activated, it keeps the body warm by burning calories. It may also increase your energy and metabolism and help control your blood sugar. That could reduce your risk of obesity and diabetes.