- In an article written by an MD regarding winter swimming who references 24 other sources found that
Repeated exposure to cold stimuli results in an increased tolerance to
cold, through a variety of adaptive mechanisms. A significant body of
evidence raises the hypothesis that these mechanisms may also confer
protection against several diseases and call for a large, prospective
epidemiological study.1
The effects found have been:
- Improved metabolic profile (decrease in insulin levels)
- Activation of the immune system
- Improved antioxidant protection1
- Cold water immersion may help symptoms of depression:
The following evidence appears to support the hypothesis: Exposure to
cold is known to activate the sympathetic nervous system and increase
the blood level of beta-endorphin and noradrenaline and to increase
synaptic release of noradrenaline in the brain as well. Additionally,
due to the high density of cold receptors in the skin, a cold shower
is expected to send an overwhelming amount of electrical impulses from
peripheral nerve endings to the brain, which could result in an
anti-depressive effect. Practical testing by a statistically
insignificant number of people, who did not have sufficient symptoms
to be diagnosed with depression, showed that the cold hydrotherapy can
relieve depressive symptoms rather effectively. The therapy was also
found to have a significant analgesic effect and it does not appear to
have noticeable side effects or cause dependence. In conclusion, wider
and more rigorous studies would be needed to test the validity of the
hypothesis.2
- In Hydrotherapy practice:
Application of hot water for less than five minutes has a stimulative effect on circulation. For more than five minutes, it is depressive and causes stasis of blood in the dilated arterioles.
Application of cold water for less than one minutes is stimulative, because the arterioles react quickly and vasoconstrict. This pumps the blood out of the periphery and into the core. For more than one minute, however, it is depressive to circulation because it causes a vasodilation. (p.30-33)
How does it cause vasodilation? Well, since the blood becomes shunted, the tissues of the vasoconstricted vasculature have no nutrients and start to accumulate metabolic waste. The increase in metabolic waste and lack of nutrients intrinsically causes vasodilation again. This mechanism is a physiological response, and scientists debate which factor of the two causes the dilation. There are therefore two mechanisms proposed, known as the "Vasodilator Theory" and the "Oxygen Lack Theory" AKA "Nutrient Lack Theory," respectively 3.
There are many different tools and methods of Hydrotherapy including neutral baths, peat baths, fomentations, russian baths, enemas, wet sheet packs, cold mitten friction, constitutionals, etc. which use these basic principles as its guiding force, but we will focus on the cold shower:
"Hydrotherapy has a great role to play in the enhancement of athletic
performance and the prevention and treatment of althetic injuries.
Kellogg did many experiments which showed that brief hot showers
followed by brief cold showers greatly enhanced work performance if
give before the activity and, if given after, significantly speeded
recovery in persons exhausted by prolonged exercise." (p.201-202)
- This can be further backed up with a meta-analysis of cold water immersion (CWI) for delayed-onset muscle soreness (DOMS) due to physical activity:
The main findings of this study were as follows: (1) CWI alleviated
symptoms of DOMS at 24, 48, 72 and 96 h post exercise and was
effective at 24 and 48 h following high intensity exercise. (2) CWI
had a small but significant effect in reducing efflux of CK post
exercise. (3) CWI had no effect on recovery of muscle strength but was
effective in improving recovery of muscle power.4
More to the point (emphasis my own),
"...correct use of hydrotherapy has an important role to play in the
prevention of disease, both chronic and acute. On one hand prolonged
hot applications in the form of warm baths, showers, hot tubs, etc.,
should be avoided because of their depressing effect on circulation,
tissue tone and the immune and nervous systems which can lead to
varicosities, premature aging, frequent colds, fatigue, and mental
sluggishness. On the other hand cold applications in the form of cool
showers, cold friction rubs, barefoot walking in the morning dew or
fresh snow, and wet socks at night are bracing treatments which can
enhance immunity against colds and flu, increase energy and stress
tolerance and improve mental and physical performance." (p.209)
Boyle, Wade, and André Saine. Lectures in naturopathic hydrotherapy. East Palestine, Ohio: Buckeye Naturopathic Press, 1988. Print.
(1) T.M Kolettis, M.T Kolettis, Winter swimming: healthy or hazardous?: Evidence and hypotheses, Medical Hypotheses, Volume 61, Issues 5–6, November–December 2003, Pages 654-656, ISSN 0306-9877, 10.1016/S0306-9877(03)00270-6.
(http://www.sciencedirect.com/science/article/pii/S0306987703002706)
(2) Nikolai A. Shevchuk, Adapted cold shower as a potential treatment for depression, Medical Hypotheses, Volume 70, Issue 5, 2008, Pages 995-1001, ISSN 0306-9877, 10.1016/j.mehy.2007.04.052.
(http://www.sciencedirect.com/science/article/pii/S030698770700566X)
(3) Hall, John E., and Arthur C. Guyton. Guyton and Hall textbook of medical physiology. 12th ed. Philadelphia, Pa.: Saunders/Elsevier, 2011. Print. pp.192-193
(4) Jonathan Leeder, Conor Gissane, Ken van Someren, Warren Gregson, Glyn Howatson . Cold water immersion and recovery from strenuous exercise: a meta-analysis. British Journal of Sports Medicine, Volume 46, Number 4 (March 2012), pp. 233-240, http://ejournals.ebsco.com/direct.asp?ArticleID=4606A5D29A0DA7DFE6DF