On November 18th this year, a girl in the UK who was dying of terminal cancer won a court case allowing her to have her body cryogenically frozen, in the hope that she could be revived in the future when a cure for her cancer (and presumably death) will have been discovered1. Cryonics, or the cryogenic freezing of whole human bodies or heads at -196 degrees Celsius, offers the promise of immortality – but at a cost of $200,000 USD for whole-body preservation at the largest facility (Alcor Life Extension Foundation in Scottsdale, Arizona). So is there a science to cryopreservation? What are the prospects of the 149 patients in Alcor’s facility rejoining the land of the living2?

Evolution offers some precedent in the science of cryonics. For example, the wood frog (Rana sylvatica) survives the winter by allowing itself to freeze during the winter and thaw in the spring. This is achieved by some clever abuses of carbohydrate metabolism, which allows for accumulation of glucose and urea in tissues on exposure to temperatures between 0 and -2 degrees Celsius. These act as a cryoprotectant for our amphibian time traveller, allowing it to survive the freezing process3. Cryopreservation of human tissues tries to replicate this through the use of glycerol as a cryoprotectant, allowing for vitrification of the intracellular fluid and avoiding the formation of ice crystals which ultimately cause cell death4.

However, a key advantage the wood frog has over humble humans is that it anticipates its demise at the hands of Jack Frost, and upregulates its enzymes by magnitudes to ensure an even distribution of glucose through its tissues3. When people are cryopreserved it is usually following a period of brain death of at least a few minutes before circulation is restored artificially. Principles of brain ischemic damage are not affected, and many neurons are probably damaged by the time any cryoprotectant manages to circulate5. Crucially, given the density of the cerebrum, it is also ultimately unlikely that all the cortical neurons are adequately supplied with cryoprotectant prior to being frozen, increasing the likelihood of intracellular ice forming and cell death on thawing. Very few people would pay $80-200 thousand USD for the prospect of returning to our mortal coil in a persistent vegetative state.

Emperor Qin Shi Huang, the first emperor of a unified China, was obsessed with immortality. He is best known for his terracotta warriors, but it is believed he died from drinking elixirs made of jade and mercury in the hope that they would prolong his life6. Modern cryonics has almost as much scientific evidence to persuade us of its success as Emperor Qin’s elixirs and none beyond our modest success at short term storage of organs and single cells. Currently all cryonics companies provide is an expensive sarcophagus with a marginal hope of success, made all the more unlikely by the requirement of medical science to find a cure for both the disease that killed the ‘patient’ and reversal of brain death itself. If, like Emperor Qin, you are hoping for eternal life, pottery classes may be a better starting point.

1. Bowcott, O. & Hill, A. 14-year-old girl who died of cancer wins right to be cryogenically frozen. The Guardian (2016).
2. Alcor Website. http://www.alcor.org/
3. Costanzo, J. P. et al. Cryoprotectants and extreme freeze tolerance in a subarctic population of the wood frog. PLoS One 10, 3461–3473 (2015).
4. Fuller, B. J. Cryoprotectants : the Essential Antifreezes To Protect Life in the Frozen State. Cryo Letters 25, 375–388 (2004).
5. Crippen, D. & Hendry, R. Brain Failure and Brain Death. ACS SurgeryPrinciples Pract. (2014). doi:10.2310/7800.2159
6. Wolff, J. Emperor Qin in the Afterlife. 20, 1–7 (2007).