Every day we’re not in lockdown - winter or summer - public health expert Grant Schofield takes the dog down to his local beach for a swim.
Taking a cold dip is effectively like "upgrading your brain", Schofield tells Kathryn Ryan.
Listen to the full interview with Grant Schofield here
Even Schofield sometimes squirms at the thought of getting into cold water, but says he's been "flabbergasted about the wellbeing effects" he's discovered via research.
"I was frankly pretty sceptical about [the health benefits]. That's why I didn't even want it to be true 'cause I look at cold water and go, 'oh my Lord, you're kidding me'.
"We started doing some measurements and our own study, [focusing] in particular on calmness, the anti-anxiety [effects]."
Cold water immersion helps remove and regulate a neurotransmitter that is implicated in depression and anxiety, in particular, Schofield says.
"But I think the cold by itself is probably not the whole story ... because when you approach cold water, I don't care who you are, there's a sort of trepidation and anxiety.
"One way to learn to control the anxiety is through modulating your breath, so this idea of nasal breathing, gentle nasal breathing regulates the sympathetic nervous system.
"There's quite a big shock [once you jump in]. You want to gasp and you want to have that whole fight or flight system up and going, but learning to regulate that is such a nice lesson for learning to regulate anxiety in the rest of your life."
The mental health benefits of cold water swimming are immense because it brings you immediately into the present, he says.
"You get to start with at least a bit of an unpleasant feeling in your forearms and your calf as the blood sort of drains away.
"It actually hurts a little bit, but noticing that without it consuming you ... it's a nice effect of drawing you into the now and noticing your [negative] thoughts rather than being consumed by your thoughts.
"I think part of the problem in psychology sometimes is we've tried to say well, that 'these things make you anxious, let's try and avoid them', and that's not necessarily how you have a fulfilled life."
As with any physical activity you're trying for the first time, and especially if you have underlying health conditions, Schofield recommends getting advice from your doctor before jumping in the water.
Photo: supplied
If you do give it a go, try and build tolerance by staying for at least 10 minutes in water that's 16 degrees or less.
"After five minutes you actually feel it's like an internal heater going off, rather than feeling cold ... you feel this heat radiating out from the inside."
People wanting to a more gentle start can try switching the shower to cold water in the last 30 seconds and building from there, he says.
To combat the 'flight or fight' response that's activated by cold water, Schofield likes to do 16 gentle nasal breaths, counting them using his knuckles and fingertips.
Another benefit of cold water immersion is that the stress response it induces turns "white fat" to "brown fat", Schofield says.
"This brown fat is highly metabolically active and like a little internal heater. So of course the stress of cold helps turn that.
"White fat tends to be fairly benign, and sometimes it's not even benign, it actually is inflammatory in excess, and brown fat is the opposite.
"Stress, whether it be exercise, whether it be some time without food, whether it be hot or cold, means that this hugely adaptive system of humanity builds itself better than it was before, and of course ... because we're such great adapters, we un-adapt at the same rate [if we're sedentary]."
Schofield hopes to see more evidence of the benefits of cold water in future research.
* Grant Schofield is an Auckland University of Technology professor of public health and director of the university's human potential centre.