What is a 'growth hormone'?
Cell division is a process that needs to be carefully controlled. Both during adulthood and also especially during early years, during development in the womb or during childhood. The body has developed a lot of very sophisticated ways to exercise that control. This one type of control circulates in the body, in other words, its a hormone, that is constructed by a particular part of the body and circulates around the body and affects other parts of the body. Human growth hormone is one of those. If we dont have enough human growth hormone in early life, then we end up not growing very much, and being short stature and so on. And some people are genetically deficient in human growth hormone and that can be cured or at least alleviated by injection of human growth hormone. So a number of people you have with problems, just get human growth hormone in childhood and that will allow them to grow to a normal height. However it is much less clear whether it is good for anything in terms of aging. It turns out that in the laboratory where we make mice genetically deficient in growth hormone itself or with some of the other proteins that the hormone interacts with, then they actually live longer, they're smaller but they live longer. This maybe because growing to a normal size is essentially an error-prone process. If we have hormonal deficiency that causes us to grow more slowly, then cell division and all the processes involved in cell division may happen a little bit more accurately so that less damage have accumulated as a side effect of of doing so and that may underlie the fact that such animals tend to live a bit longer. If we have normal levels of growth hormone early in life but later in life we add some more, then that may have some benefits that certainly does help, in some people, to alleviate and even reverse the loss of muscle mass that happens during elderly life. On the other hand, it may be that having too much growth hormone late in life may increase one's risk of cancer, because of course cancer is cell growth and division, and if we do that too much then the cancer grows more quickly, in principle. It may be that some people will be worth to take growth hormone because they are not in danger from dying anytime soon from cancer but they are suffering alot of loss of muscle mass and for some other people it may be the other way around. However I want to emphasize that there's an awful lot we don't know about this at the moment so we need more data.
