Rejuvenation is a medical discipline focused on the practical reversal of the aging process.
Rejuvenation is distinct from life extension. Life extension strategies often study the causes of aging and try to oppose those causes in order to slow aging. Rejuvenation is the reversal of aging and thus requires a different strategy, namely repair of the damage that is associated with aging or replacement of damaged tissue with new tissue. Rejuvenation can be a means of life extension, but most life extension strategies do not involve rejuvenation.
Historical and cultural backgrounds
Various myths tell the stories about the quest for rejuvenation. It was believed that magic or intervention of a supernatural power can bring back the youth and many mythical adventurers set out on a journey to do that, for themselves, their relatives or some authority that sent them.
An ancient Chinese emperor actually sent out ships of young men and women to find a pearl that would rejuvenate him. This led to a myth among modern Chinese that Japan was founded by these people.
In some religions, people were to be rejuvenated after death prior to placing them in heaven.
The stories continued well into the 16th century. A famous Spanish explorer Juan Ponce de León led the expedition around the Caribbean islands and into Florida to find the Fountain of Youth. Led by the rumors, the expedition continued the search and many perished. The Fountain was nowhere to be found as locals were unaware of its exact location.
Another commonly cited approach was attempting to transfer the essence of youth from young people to old. Some examples of this approach were sleeping with virgins or children (sometimes literally sleeping, not necessarily having sex), bathing in or drinking their blood.
The quest for rejuvenation reached its height with alchemy. All around Europe, and also beyond, alchemists were looking for the Philosopher's Stone, the mythical substance that, as it was believed, could not only turn lead into gold, but also prolong life and restore youth. Although the set goal was not achieved, alchemy paved the way to the scientific method and so to the medical advances of today.
Serge Abrahamovitch Voronoff was a French surgeon born in Russia who gained fame for his technique of grafting monkey testicle tissue on to the testicles of men while working in France in the 1920s and 1930s. This was one of the first medically accepted Rejuvenation Therapy (before he was proved to be wrong around 1930–1940). The technique brought him a great deal of money, although he was already independently wealthy. As his work fell out of favor, he went from being a highly respected surgeon to a subject of ridicule. By the early 1930s, over 500 men had been treated in France by his rejuvenation technique, and thousands more around the world, such as in a special clinic set up in Algiers. Noteworthy people who had the surgery included Harold McCormick, chairman of the board of International Harvester Company, and the aging premier of Turkey.
Aging is an accumulation of damage to macromolecules, cells, tissues and organs. If any of that damage can be repaired, the result is rejuvenation.
There have been many experiments which have been shown to increase the maximum life span of laboratory animals, thereby achieving life extension. A few experimental methods such as replacing hormones to youthful levels have had considerable success in partially rejuvenating laboratory animals and humans. There are at least eight important hormones that decline with age. In theory, if all or some of these hormones are replaced, the body will respond to them as it did when it was younger, thus repairing and restoring many body functions. Yet another option involves cosmetic changes to the individual to create the appearance of youth. These are generally superficial and do little to make the person healthier or live longer, but the real improvement in a person's appearance may elevate their mood and have positive side effects normally correlated with happiness. Cosmetic surgery is a large industry offering treatments such as removal of wrinkles ("face lift"), removal of extra fat (liposuction) and reshaping or augmentation of various body parts (abdomen, breasts, face). There are also, as always in history, many fake rejuvenation products that do not work. Chief among these are powders, sprays, gels, and homeopathic that claim to be "growth hormone". Authentic growth hormone can only be injected, because the 191 amino-acid protein is too large to be absorbed through the mucous membranes, and would break up in the stomach if it is swallowed. 
To rejuvenate effectively and, thus, to prolongate your active life, you should be engaged in physical exercises. The 80-year-old athlete, who has been exercising properly, is depicted at the right image and may be an example. Such result cannot be achieved by applying any modern rejuvenation theory, by the way.
- iPSc as a result of radical rejuvenation
- Strategies for Engineered Negligible Senescence
- Regenerative medicine using pregnancy specific biological substances
- Regenerative Medicine using Non-Fetal Stem cell sources
- Fetal tissue transplantation in Regenerative Medicine
- Cord Blood Science and its Frontiers
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- How can regenerative medicine impact cardiology?
- SENS Foundation
- Regenerative Medicine and Rejuvenation
- Life Extension magazine interview about rejuvenation science
- Resources and Articles on the Biology of Aging and Life-Extension
- The Biogerontology Research Foundation - a UK-based charity focused on rejuvenation research
- Aging Cell - an online publication covering the novel rejuvenation mechanisms