Hormesis

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In toxicology, hormesis is a dose responsephenomenon characterized by a low dose stimulation, high dose inhibition, resulting in either a J-shaped or an inverted U-shaped dose response. A pollutant or toxinshowing hormesis thus has the opposite effect in small doses than in large doses.

As an example, challenging micewith small doses of gamma rayradiation shortly before irradiating them with very high levels of gamma rays actually decreases the likelihood of cancer. There is a similar effect when dioxinis given to rats. The same has long been proposed regarding moderate ambient temperature fluctuations, regular exercise and even limited caloric deprivation, as both immune system stimulants and possible longevity factors. The hormesis model has been shown to hold for numerous other substances and environmental fluctuations. Hormesis, then, is the term for generally-favorable biological responses to low exposures to toxins and other stressors. (Such environmental factors that would seem to produce positive responses have also been termed "eustress".)

Possible explanation

The reason for the hormesis phenomenon is not completely understood. It is conjectured that a low dose challenge with a toxin may jump start certain repair mechanisms in the body, and these mechanisms are efficient enough that they not only neutralize the toxin's effect, but even repair other defects not caused by the toxin. This is similar in principle to viral vector vaccinesunder development for diseases such as cancerand AIDS.

Similarly, continuing or intermittent mild stressors such as exercise, environmental fluctuations and even food limitations would seem to stimulate tolerance to sudden similar but more severe demands made upon the organism.

Policy consequences

Traditionally, regulatory agencies such as the Environmental Protection Agency(EPA), the Food and Drug Administration(FDA), and the Nuclear Regulatory Commission(NRC) use a threshold modelfor non-carcinogens, and a linear no-threshold modelfor carcinogens (including radiation). In the threshold model, anything above a certain dose is considered dangerous, and anything below it safe. In the linear model, there is no safe dosage. Changing to a hormesis model would likely change exposure standards for these toxins in air, water, foodand soil. As a result, costs of environmental regulations and cleanup/remediation activities could be lowered.

Wider use of the hormesis model would affect how scientistsdesign and conduct studies and the selection of statistical modelsthat estimate risk.

The study of hormesis has been best developed, perhaps, in the field of ionizing radiation.

The United States based National Council on Radiation Protection and Measurements(NCRP), a body commissioned by U.S. Congress, recently released report written by the national experts in the field which states that, for the sake of caution, radiation's effects should be considered to be proportional to the dose an individual receives, regardless of how small that dose is. This report squarely rejects almost all research showing hormesis as being flawed in some way (i.e. the cancer a study focuses on does not exist in humans, a clear threshold could not be established in humans, the assumptions are seriously flawed).

In the absence of policies to accept hormesis, and with hundreds of billions at stake, as well as many people's livelihoods, the controversy is very active.

Low doses always beneficial?

While the most prominent cases of hormesis show low doses of toxins showing beneficial effects, this is not part of the definition of hormesis. The key is that low doses show the opposite effect of high doses. There are substances where low doses show detrimental effects not seen in high doses, (such as in routine low dosage of animals or humans with antibiotics?)

Medical and Veterinary uses

The concept of hormesis is now being used to:

• Enhance cognitive function in patients with neurodegradative diseases such as Alzheimer's disease.
• Boost immune function to prevent diseases in people, captive-breeding populations of both ectothermicand endothermicanimals and in commercial fisheries.
• Avoid harmful tumor-promoting effects of anti-cancer drugs.

Controversially, some homeopathicresearchers and practioners claim that their use of homeopathic preprations diluted beyond Avogadro's number (such that no molecules of the original solute are present) represent an extension of the principle. This is based on energetic concepts and is widely dismissed by science and medicine, but is accepted by energy healing practitioners and the theories of energy healing. Science similarly does not support such practices.

Slow acceptance

The acceptance of the hormesis model of dosage response has been slow. Reasons may include:

• Unproveable in an ethicalstudy of humans. This may change now that Chernobyl studies are starting to show far fewer deaths than the no-threshold hypothesis would predict. Michael Fumento on Tech Central Station
• Counterintuitive result.
• Toxicology experiments have typically used very few doses and emphasized high doses, thus missing potential hormetic phenomena.
• Hormesis was associated with the medical practice of homeopathyin its early years and was stigmatizedas a result.

See also

• Petkau effect
• Stochastic resonance

Source

An early version of this article was based on the press handout: "Hormesis: Principal Concepts and Take Home Message", by Edward J. Calabrese, Ph.D., University of Massachusetts, from a hormesis panel discussion, Feb 25, 2004, Washington, DC. A large amount of information is available from the BELLE (Biological Effects of Low Level Exposure) website [1]

Theory and Philosophy

The idea of hormesis is actually quite frequently encountered though rarely named. Strength trainingand Bodybuilding, for example, are examples of hormesis.

The body's neurological recruitment of muscle fibres is increased with practice and with increasing weights, similar to the way balance and co-ordination and special skills are acquired in sports. Strength training emphasizes these types of strength gains. Learning itself, gains in intelligence and knowledge, may be thought of Hormesis, as well as forms of stress suppression.

When exercised to failure with heavy weights to induce hypertrophy, with adequate protein and rest to rebuild the fibres, the body will overcompensate and rebuild the muscle fibreslarger. This leads to higher gains in strength, as larger tissues can contract harder and take more load. Due to this, efficient muscle fibre recruitment is not as necessitated by the body and mind, and will probably not be developed as much. Bodybuilding emphasizes this form of strength gain which also includes size gain, but a low strength to weight ratio. Gains in weight are not desired among athletes who do a great deal of movement or acrobatics, or who do movements that stress the joints in ways the body can not adapt.de:Hormesis es:Hormesis

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It uses material from the http://en.wikipedia.org/wiki/Hormesis Wikipedia article Hormesis.