hibernating bears and nasa -- 3/3/21
Today's selection -- from Packing for Mars by Mary Roach. The effects of zero gravity on the human body are significant -- balance problems, visual disturbances, damage to the heart muscle and bone loss. However, maybe hibernating bears can help:
"Black bears emerge from their dens after four to seven months in bed with bones as strong as when they turned in. There are researchers who believe that hibernating bears may hold the key to treating and preventing bone loss. I talked to one of them, Seth Donahue, an associate professor of biomedical engineering at Michigan Technological University. Donahue said that hibernating bears' bones break down, just like bed-resters' and astronauts' bones. What's different is that their bodies take the calcium and other breakdown minerals out of the blood and reapply it to their bones. Otherwise the calcium level in their blood would build to lethal concentration. Because during those four to seven months, the bears don't get up to go to the bathroom. All the bone minerals that get dumped in the bloodstream as the bones dismantle themselves would stay there, accumulating. 'So they've evolved a method to recycle that calcium.' And therefore not die. The bone protection is 'a lucky consequence.'
"Donahue and others have been studying the hormones that control bear metabolism to see whether they can identify some component that will help post menopausal women (and astronauts) grow new bone. They've nominated bear parathyroid hormone. Donahue has a company that makes a synthesized version, injections of which are being tested in rats and eventually, if all goes well, will be tested in postmenopausal women. Even human parathyroid hormone makes women grow bone. It's one of the most effective ways to increase postmenopausal bone density. Unfortunately, high doses make rats grow bone cancers, and thus the Food and Drug Administration limits prescriptions to one year and for women who've already had fractures. Donahue said bear parathyroid hormone doesn't appear to have any adverse side effects, so keep your claws crossed that it pans out.
"There's another reason hibernating bears are interesting to NASA. If humans could be made to hibernate, to breathe one-fourth as much oxygen and eat and drink nothing for six months of a two-to-three year Mars mission, imagine how much less food and oxygen and water one would need to launch. (The less baggage on board a spacecraft, the cheaper it is to launch. Once it reaches the speed needed to escape the pull of Earth's gravity and leaves behind the air drag of Earth's atmosphere, a spacecraft basically coasts to Mars.) Each extra pound of weight launched adds thousands of dollars to the project budget. ...
"Do space agencies ever discuss human hibernation? They have, and they do. 'It never dies,' says John Charles. 'It just hibernates.' Charles puts little stock in the possibility. 'Even if it did work, would we really short-supply a crewed vehicle on a three-year mission to Mars? What if the hibernaculum malfunctioned, and everyone woke up? How much food and oxygen do you carry, just in case? And when is that amount sufficiently large that the savings due to hibernation are lost?'
"Here's another reason it won't work. Hibernating bears derive all their water and energy from reserves of fat that they build up by bingeing before they den. According to the Bear Center at Washington State University, a small (astronaut-sized) bear gorging on apples and berries consumes up to 40 percent of its body weight each day during this period. That's about 65 pounds of food a day.
"Six months of living on nothing but fat -- even your own -- probably isn't healthy unless your body has somehow adapted to it. Little known fact: Hibernating bears have high 'bad' cholesterol levels. (They also have very high 'good' cholesterol -- which probably explains why heart disease is unknown in bears.)"