When I took Physics courses in college, I learned about how astronauts should age a tiny bit slower than us. Of course, they would be exposed to a lot more radiation so they might develop more cancers. But all in all, I would have been excited about the prospect of living in space.

Then the astronauts came back and we saw them being barely able to walk. Yet these were young men selected among thousands for their physical fitness. That was explained away by saying that the lack of gravity meant a lack of exercise. All these astronauts needed was a good workout. And future astronauts would have a “space gym” so it would all be alright.

But then more results started coming back. Not only do astronauts come back with weak muscles and frail bones… But they also suffer from skin thinning, atherosclerosis (stiffer arteries), resistance to insulin and they suffer from loss of vision due to cataracts many years earlier than expected given their chronological age. These symptoms look a lot like skin aging, cardiovascular aging, age-related diabetes and so forth. In fact, it is pretty accurate to say that astronauts age at an accelerated rate. This is despite the fact that the current generation of astronauts follows a rigorous exercise program. They are also followed medically more closely than just about anyone on Earth: they don’t indulge in regular fast food.

Trudel, one of the leading researchers on this front appears to think that lack of sufficiently strenuous exercise is the problem. He observed that resting greatly accelerates aging:

“(…) after 60 days of bed rest, the marrow of the patients studied looked as if it had aged and grown by four years” (motherboard)

When not attributed to a lack of sufficient exercise, many of these effects seem to be attributed to an increased exposure to radiation. Indeed, astronauts in the International Space Station are exposed to about ten times as much ambient radiation as the rest of us. However, there is only so much you can explain away with a slight increase in radiations. For example, people exposed to radiation grow cancers, they don’t develop diabetes. And even cancer is not a given: a small increase in radiation exposure can actually make you healthier through a process called hormesis. In fact, that’s precisely what exercise does: it is a stress on your body that makes you healthier. In any case, we do not know whether astronauts are more likely to die from cancer. Certainly, they don’t all fall dead at 40 from cancer… If there is an increased rate of cancer, it is fairly modest because, otherwise, we would not be worrying about how their skin is getting thinner.

So it looks like despite short stays, and very attentive medical care, astronauts age at a drastically accelerated pace… not just in one or two ways but across a broad spectrum of symptoms.

I looked as hard as I could and I could not find any trace of medical scientists worrying about such a phenomenon a priori.

What is going on? Why does life in space accelerate aging so much?

Gravity seems to play a key role:

The more likely culprit is the relative lack of gravity in a microgravity environment, which scientists think has a negative influence on (…) metabolisms. (Peter Dockrill, Science Alert)

Further reading: