Cold water has a marked impact on the bodies of mammals, especially those that have evolved to spend most of their time in the water.  This is evidenced by the ‘mammalian dive response’.  An evolutionary adaptation designed to help mammals survive underwater for as long as possible, due to the lack of breathable oxygen.  This same response can have unexpected positive effects on the mammalian brain, and occurs naturally in humans.

EFFECTS OF THE MAMMALIAN DIVE REPONSE

When a mammal’s face touches cold water, the dive response begins.  In humans, the heart rate decreases by around ten to twenty-five percent.  The effect is way stronger in seals, who’s effective heart rate can decrease by up to 92 percent.  If diving, the increasing water pressure on the facial area around the tear ducts  and nose causes a vasoconstriction (narrowing of the blood vessels) on the extremeties (hands/feet etc), as the facial nerves perceive a dive and attempt to conserve oxygen in the blood for use by the brain and heart.

HELD BREATH VASODILATION (INCREASED BLOOD FLOW TO THE BRAIN through ELEVATED CO₂ LEVELS)

Scientists studied the effect of the simulated dive response in rats, by artificially increasing the CO₂ levels in their blood, and found that the blood vessels in the brain dilated considerably, resulting in a 1.5 fold increase in blood flow to the brain due to hypercapnia, ( the technical term for an increase in carbon dioxide in the blood stream).  If you hold your breath while holding your head in cold water, you can potentially have a double effect of the mamalian dive response, coupled with the vasodilation response that occurs naturally when holding your breath.

The vasodilation response in particular helps to shunt blood-flow to the brain by relaxation of the blood vessels, most importantly the carotid arteries.

WHY DOES ALL THIS MATTER?

Using these techniques we can temporarily increase our awareness, while relaxing our nervous and muscle system, along with our heart rate.  This should be especially helpful for people who become stressed easily.  Holding our breath can be likened to breathing into a paper bag to stop anxiety attacks. When coupled with the added physical response caused by the dive response, this can be a powerful and life changing experience. I hold my head in cold water most mornings. You will notice that as soon as you do it there is a marked decrease in heart rate and an increase in muscular relaxation, which is a great way to help start the day motivated and ready for anything.  You will also notice that when your heart rate slows and you chill out, you can hold your breath for noticeably longer periods of time.

WHY IS IT GOOD FOR WEIGHT LOSS?

Well, this is really conjecture, but…  Many of us comfort eat when we are stressed, therfore, if we can do certain things that provide a direct relaxation effect to our nervouse systems, we are essentially arming ourselves with a readily available hack to calm ourselves down.  This may not work for everyone, but I hope it will work for some.

Why not try it every day for a week and see whether it works for you, you ain’t got nothing to lose, except for maybe a bit of bodyheat from your face!

For more information on how cold water could be good for weight loss, please see my post on cold water swimming.

references:

http://ajpregu.physiology.org/content/274/4/R921.short

http://www.winwenger.com/ebooks/guaran3.htm