Furthermore, there is no evidence that growth hormone treatments increase longevity. Indeed, mice that overproduce growth hormone die sooner than normal mice, and fruit flies that underproduce growth hormone live longer than normal flies. In addition, some researchers suspect that supplementary growth hormone may increase the risk of cancer.
DHEA is the most abundant steroid in the body, yet nobody knows much about what it does. It is clear that DHEA levels peak in a person's early 20s and decline as he or she ages. Interestingly, feeding DHEA to mice, which produce very small quantities of this hormone naturally, increases their life spans by 40 percent. In Why We Age, Steve Austad notes that in the few scientifically valid human trials involving DHEA supplementation, the hormone produced "some improvement in immune response, muscle strength, and sleep patterns among the elderly."Still, not much is known about the effects of the long-term use of this hormone, so most researchers advise caution.
Much has also been made of the so-called "melatonin miracle." But rigorous testing of melatonin's effects on human beings has not been done yet. Mice that are fed melatonin live 5 percent longer but are at a greater risk of developing tumors. Again, most researchers advise caution.
So far, estrogen replacement therapy is the most effective hormone treatment. Epidemiological evidence suggests that supplemental estrogen after menopause helps prevent osteoporosis. But recent research has undercut claims that estrogen therapy reduces the risk of heart disease and dementia. Using estrogen does slightly increase the risk of ovarian cancer and promotes the growth of existing breast tumors. Estrogen may delay the onset of certain diseases that become more common as women grow older, but there is no evidence that it increases users' life spans.
Testosterone levels generally drop in men as they age. Research on testosterone has lagged behind estrogen research, perhaps because of the unsavory treatments of the past and perhaps because of steroid abuse among athletes. There are some indications that testosterone replacement can provide benefits to older men, including increasing muscle tone, overcoming erectile dysfunction, and improving their overall sense of well-being. On the other hand, it might promote the growth of any pre-existing prostate tumors. There are other unwelcome side effects, including increased hairiness and acne. And there is no evidence that testosterone supplementation will increase longevity.
The Genetic Imperative
Looking further down the road, once the genes that promote disease (Alzheimer's, diabetes, cardiovascular problems) and those that promote longevity are identified, it will become possible for parents to select favorable genes for their progeny. Already, more than 1,000 healthy children have been born after their parents used pre-implantation genetic diagnosis to select among eight-cell embryos to find the ones that were free of disease genes. In the future, parents might also select embryos that bear longevity-promoting genes and implant those. Further in the future, parents will be able to add genes that improve their progeny's immune systems, mental acuity, and athletic abilities by installing artificial chromosomes.The Cambridge gerontologist Aubrey de Grey wants to genetically engineer mitochondrial genes into the nuclei of cells, where they would be better protected from the ravages of free radicals. He believes that once those genes are better protected they will not be so quickly mutated into the free radical death spiral. Once the vicious circle of mitochondrial mutations producing ever more free radicals is broken, longer life should result, he argues.
Even further in the future, another method to improve how human cells protect themselves from the ravages of free radicals might be possible. Some animals, such as birds, have more effective anti-oxidant protective mechanisms. Using them as a model, we might tweak our own genes. This could be the moral equivalent of replacing human anti-oxidant genes with similar but more effective genes from birds.
An even more visionary approach has been suggested by Robert Bradbury, whose startup Robiobotics is investigating the possibility of repairing whole genomes by using bacteria to ferry artificial chromosomes into human cells. The genetically engineered bacteria would infect billions of a patient's cells and deliver artificial chromosomes carrying a suite of hundreds of genes specifically aimed at repairing the damage done by free radicals. Some genes on the artificial chromosomes might be replacements for damaged genes; others would be designed to enhance cellular DNA repair.
Skeptics point out that our immune systems would likely do in Robiobotics' designer bacteria, but Bradbury suggests that the problem might be dealt with by using a transitory immunosuppressive therapy that would give the genetically engineered bacteria an opportunity to reach their desired cellular targets.
Nanomedical Insurance
But this focus on biological interventions may be wrongheaded. After all, some argue, we don't fly because we sprouted wings, so neither will we live longer because we've fiddled with our genomes. Why not make machines that hunt down harmful disease organisms and repair damaged cells? That is the ambitious aim of nanomedicine.Nanotechnology is the science and technology of building devices using single atoms and molecules. A nanometer is a billionth of a meter, a length that is just over the diameter of many atoms. Conceptually, nanotechnology and biotechnology are not all that distinct. In the words of Rita Colwell, the director of the National Science Foundation, "Life is nanotechnology that works."
Proponents of medical nanotechnology -- such as Ralph Merkle, a former research scientist at Xerox's Palo Alto Research Center and now a fellow at the Texas nanotech company Zyvex -- outline an ambitious vision. "Nanotechnology will let us build fleets of computer-controlled molecular tools much smaller than a human cell and with the accuracy and precision of drug molecules," Merkle declared in the Winter 1999 issue of the Anti-Aging Medical News. He added, "These machines could remove obstructions in the circulatory system, kill cancer cells or take over the function of subcellular organelles." Robert Freitas, author of the 1999 book Nanomedicine, foresees a day when oxygen-carrying red blood cells could be supplemented by artificial respirocytes made of carbon that would be 200 times more efficient.
If that isn't wild enough, Freitas recently unveiled a scheme that would replace your entire circulatory system with a sapphire vasculoid weighing two kilograms. No heart, no blood -- just a system of nanotech machines that would ferry oxygen, carbon dioxide, nutrients, and immune protective machines throughout your body, all encased in nearly unbreakable sapphire that would line your old-fashioned veins and arteries. Since 80 percent of what kills most people can be traced to the circulatory system -- heart attacks, strokes, wounding, metastasizing cancer -- such a vasculoid would dramatically increase one's life span. Freitas thinks the first models will be available in 40 years.
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