The mysterious aging of astronauts

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:

Daniel Lemire, "The mysterious aging of astronauts," in Daniel Lemire's blog, December 1, 2015.

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Daniel Lemire

A computer science professor at the University of Quebec (TELUQ).

39 thoughts on “The mysterious aging of astronauts”

  1. Maybe they do get more cancer, but because they are “followed medically more closely” they detect it early.

    1. We actually do expect astronauts to experience more cancers…

      Medical scientists have reported just about every bit of trouble that the astronauts experience… but nothing on an increase of cancer rates. We have no reason to believe that scientists would keep this information secret while divulging information about insulin resistance, say.

      So the most reasonable assumption is that if there is an increase in cancer rates, it is not huge. I personally think that there is an increase but if it might be no stronger than, say, taking up smoking. If so, you will have a hard time measuring the effect in a small population.

      This apparent lack of huge increase in cancer rates puts a dent in the theory that the accelerated aging is explained away entirely by increased exposure to radiation. If the radiations were so bad, you’d spot cancers well before you worry about diabetes or skin thinning.

      If you mean that astronauts are less likely to die of cancer because of early diagnostics… again, my argument would be the same: if astronauts commonly get diagnosed early for cancer… that would get reported.

      So “something” is going on and it is not Martians nor evil spirits, and it is probably not radiation alone.

      1. Just because there’s no increase in cancer, doesn’t mean that the radiation isn’t the cause of these other health problems. Radiation causes cancer by causing damage to DNA, but it’s not like radiation specifically targets the DNA; it damages any molecules that make up the human body that it strikes. The skin damage, the insulin resistance, the atherosclerosis, and so on, could all be caused by other parts of these respective cells and tissues being damaged.

        Outside of the astronaut population, I don’t think we’ve ever researched how elevated, ambient, full-body radiation over a period of weeks or months might affect the human body. All we’ve had to work with is sudden, massive exposures either body-wide (e.g., nuclear bombs, the “demon core” and similar incidents) or concentrated in a single area (e.g., medical X-rays, accidental ingestion/inhalation of radioactive material). Now perhaps we’re seeing how long-term, full-body exposure to radiation causes all sorts of permanent cellular or tissue damage beyond cancer.

        1. Except we do have groups of people living in conditions with increased radiation their entire lives. Either due to increased height (Nepal, Andes) or due to higher levels of background radiation. I personally think the most likely cause is lack of gravity, since it really messes up a number of things we take for granted: fluids being pushed towards your feet, etc. There are certain chemical processes that are easier to do in zero g, might not there also be chemical processes that are harder to do? And either of those can cause premature aging.

          1. Exactly what I was thinking Vettir. The loss of tensile forces changing ECM or some other critical chemical component of these tissues. Alternatively, perhaps changes to protein expression due to biophysical changes in key receptor proteins within parenchymal or immune cells. Very interesting phenomenon.

          2. Gravity is needed to create the stress fields that force movements of the various compounds of life inside and outside cellular walls.

            Some experiments comparing sea mammals to their on shore cousins could help isolate the areas of difference.

            Or studies of various amphibious reptiles and mammals that force individuals to stay in or out of the water for side effects.

  2. Stress?

    Stress is many times mentioned as the catalyst of several deseases. I cannot provide any correlation or any kind of data in this area, but it seemed as a valid option. On the other hand, to know if this is true, these symptoms should be searched for in other stress related professions.

  3. I recently watched a video guided tour of the International Space Station presented by Suni Williams, on the last day of her four month tour up there.
    I was struck by a couple of things: the confinement of the environment, and the absolute rest that weightlessness imposes on the body: she was wearing shorts, and her legs appeared rather wasted and hypotonic. She struck rather odd postures that would only be natural in zero-G throughout.
    Although she demonstrated the gym equipment that is designed to counter this well-recognized hazard of weightlessness, I was left with the impression that this was insufficient. And this after only 4 months.
    In short, my hunch is that gravity’s good for you, and adding some back in to the space environment would be an intervention worth testing, if the health effects are as you say.

    1. Yes. Could be the lack of gravity. But why would lack of gravity give you stiff arteries or insulin resistance?

      It is also a bit strange that they can’t manage to fight back muscle wasting. We are sending people in space and we can’t keep their muscles in shape?

      You’d think that space travel would be harder than muscle building.

      1. Every aspect of our body evolved in an environment where it is constantly pulled downward. Perhaps all manner of internal cellular functions (e.g., the metabolic pathways that respond to insulin by taking up glucose) go haywire without this influence on them.

        Insulin resistance and atherosclerosis are also specifically conditions that people here on earth suffer as a result of a sedentary lifestyle; perhaps the absolute zero-G environment is like a massively over-exaggerated version of the same. One day in zero G is like sitting on the couch for a week or whatever.

  4. Perhaps the effect is due to lack of grounding.
    Life is a chemical process and chemical reactions require an electric potential. Possibly in space there is not enough voltage difference to enable all of the required life processes. In particular Enzyme Pathways.
    Has anyone tried an electric field gradient head-to-toe while the astronauts are sleeping?

  5. Hydrostatic pressure?

    We are bits of ocean that learned to walk on dry land and have many adaptations to handle the variations in pressure induced by gravity, respiration, circulation, locomotion, etc. There are several systems (e.g. lymph) that are affected by mechanical action. All of these would be severely affected by weightlessness.

    For the earth-bound, prolonged immobility (e.g. sitting at a desk, or standing at a checkout desk) is in the news as a similar health risk, and may have a similar effect.

  6. This is interesting… my first thought is that time has sped up in space.
    This could just be the effect of large bodies effect on time-space as a body moves away from earth. For instance, Global Position Systems take into account the time difference in space versus time on the ground. A good experiments take two very precise clocks synchronized at ground level. One, is then taken up to a hire elevation and after a time the clock at the hire elevation has been running much faster. It’s a guess, and it might be a dumb guess at best. Could that small time spent in space cause long term effects on the bodies internal clock if there is such a thing?

  7. First, assuming all those bits of evidence really line up…

    The entire evolution of life on our planet was under gravity and earth background-level radiation. Possible we are dependent, in some way.

    The Longevity Project found a correlation between exercise, long life, and mental activity. Correlation is not proof of causation, of course.

    Watched a TED video recently, where they found mice grew more new neurons with exercise. Of course, mice are not humans, but taken with the prior, makes a strong case.

    Aside from the lack of gravity (and more limited exercise), is the environment of a space station too simple, just not mentally stimulating? (We would like to think being in Space is pretty cool, but the reality is weeks and months in a small metal box.)

    Just simple routine movements in gravity are a low level whole body exercise. Too little of this constant low level exercise might have an impact.

    The simplest (ha!) experiment would be to put up a spinning-wheel space station of size to simulate earth-level gravity. If the effects go away, weight and movement is core.

  8. Just speculation, of course, but I would think that weakening of muscles and bones is not the only consequence of weightlessness. Flow of blood, metabolism and basically everything in our body has adapted to work at about 9.81m/s^2 gravitational acceleration. I wouldn’t know what the exact cause would be, but I don’t see any reason as to why anything at all in human body should work as intended without gravitation.

  9. I think you’re too dismissive of the potential role of radiation. It’s a contentious area of research because powerful lobbies need radiation exposure to be perceived as relatively minor. Why wouldn’t you expect radiation to induce diabetes? Something like an X-Ray spikes catecholamines way up, which is consistent with other things that cause diabetes.

  10. Mice studies on ISS showed all die in 6 months from colon cancer.
    Mice hair turns gray, falls out and then they die of colon cancer.
    Space AIDS (Auto Immune Deficiency Syndrome) will be a big problem for space trips. ISS is mainly affected by microgravity.
    Radiation may not be the largest problem.

    Univ. of AZ developed a microarray and determined the thymus shrank on mice in space. AIDS patients, premature babies, elderly humans all lose thymus tissue as they age.
    The thymus trains T Cells made by stem cells to respond to infections. As humans age T Cells become unique to just a few stem cell lines. Space may cause stem cell lines to rapidly diminish.
    Space accelerates aging. ISS is really an aging research lab.

    Can NASA realize that biology will make space travel possible?
    Will US develop biology in schools to address the costs related to biology on earth? Sepsis is the fastest growing disease in US hospital ICU’s. Sepsis will kill most astronauts in space during long missions.

    Nasa is now using a tiny DNA sequencer on ISS.

    [This comment was shortened by the blog owner.]

  11. Fascinating.

    I am particularly intrigued by the idea of gravity dependence. It makes a sort of intuitive sense that blood vessels (as well as most of the cells of the body) would have to work considerably harder in the presence of gravity, and the loss of this workload in weightlessness would lead to atrophy regardless of any macro-scale exercises (treadmills, etc) that might be performed by space dwellers.

    Is this same accelerated aging observed in mice who have spent a reasonable period in space? If so, the gravity dependence question might be clarified by a rather simple experiment.

    The idea would be to make a mouse habitrail environment in the shape of a torus and then spin it to simulate gravity. This is basically the same idea as the spinning toroidal living areas seen in many space based sci-fi novels, the main difference being that this one could be quite small… perhaps 1 meter in diameter. The experiment could be run over a single mouse lifetime rather a human life time and could include a fairly large number of mice.

    In fact, the idea is simple enough that it may already have been performed. Has anyone spun mice in space to simulate gravity? If not, perhaps someone should?

  12. It’s precisely because they aren’t eating fast food!

    I’m only half joking. You can argue it either way. Fast food is bad for you therefore it stresses your body and your body gets stronger as a result. Fast food is full of preservatives and other essential nutrients that they aren’t getting on their astro diets. Fast food makes lot of people happy. Happy people live longer (or so the internet told me).

  13. Perhaps the lack of atmosphere-filtered sunlight. Some think that sunlight is a necessary nutrient for our bodies.
    Maybe something else about Earth is necessary? The Schumann Resonance? Other fundamental resonances? Regular microbial interactions via air and food? Some subtle electrical effect present on the ground and/or atmosphere?
    Then there is stress: Working on critical experiments in a wholly monitored & controlled situation must be somewhat stressful. Being inside a tin can in an inhospitable environment might exert some chronic stressors.
    Or maybe it’s more psychological: Experiencing the incredible vastness of space outside your windows…? Reflecting on that level of infinity? Perhaps that knowledge ages you?
    Or perhaps something to do with time relativity: The ISS is zipping around the Earth at 17,000+ mph, orbiting once every 90 minutes… that’s pretty fast for a human. Perhaps like the infamous “2 atomic clocks flown in different directions” experiment they are experiencing some relativistic time dilation impacts, subtle enough to miss in instruments, but not by human cells.

  14. I would hypothesis that spending 60 days underwater with some dry suit or wet suit, even without the radiation, would yield similar results as 60 days in microgravity. The buoyancy would have the effect of no gravity related stressors on the organs, muscles and skeletal structure, much more so than lying in a bed where gravity still pulls you down. The air pressure in the dry suit would have to be such where the diaphragm needs no exertion from the outside water pressure where lying in bed still does as gravity wants to pull down your rib cage.

  15. Actually, the body is not aging rapidly, it is rapidly acclimatized to the new space environment.

    So while thickness of skin might decrease, fatty layers might increase (with sufficient supplies).

    Because in space you don’t need thicker skin, it just grows to what is required. (For example)

  16. There’s been some good comments above. One thing that’s occurred to me – and that I’ve only seen been changed somewhat recently on the ISS – is that of lighting. In the very late 1990’s, scientists discovered melanopsin on frogs’ skin. We then discovered we have that on our retinas. Almost every living thing has it, as a “trigger” for the circadian clock.

    We’ve found that artificial light at night does some strange things to the body. Since blue light suppresses melatonin, other hormone levels remain raised. Suppressed melatonin has been linked to all kinds of things like prostate/breast cancer, diabetes, weight gain (on Earth anyway), obviously lack of sleep, and other ailments.

    Of course, I doubt it’s as simple as that. Microgravity is not something the body evolved to deal with, and the radiation levels / lack of sufficient exercise, and perhaps other things we haven’t even thought of yet – singly, or in combination, have a part to play in this.

    Interesting post!

  17. Have you guys heard about the entire field of study that is aerospace medicine? I’m taking a course on it this semester (I’m a masters student in aerospace engineering)–let me summarize some of the problems that your body goes through during space travel.

    Humans spend about 70% of their time either standing or sitting. That means the human body is optimized for a hydrostatic pressure gradient like the one illustrated here ( Blood pressure is much higher at your feet than at your head. In space, however, there is no gravity to produce this gradient, so the cardiovascular system equalizes its pressure. That’s why astronauts suffer from “puffy face” (higher-than-usual fluid pressures in head) and “chicken legs” (lower-than-usual fluid pressures in legs). In their first couple days in space, astronauts lose about 1L of leg volume from each leg.

    The CV system relies on internal pressure sensors to figure out how to operate, and the new pressure distribution confuses it. Astronauts lose a lot of blood plasma–it sort of ends up absorbed into the surrounding tissues. This increases the relative concentration of red blood cells, which triggers the body to slow down production of new ones. Also, the heart atrophies because it doesn’t need to pump as hard to move liquid around the body.

    When you come back from space, your body needs to rapidly readapt from microgravity to one gee. It is not very good at doing that. That’s why 63% of astronauts are unable to stand for ten minutes straight just after their return from short-duration space missions (see video:

    There are other problems: the cells that are constantly building and destroying your bones fall out of alignment when you’re in microgravity, causing astronauts’ bones to change structure in a way that looks a lot like accelerated aging. Why? Not clear, but possibly related to the lack of repeated loading, as happens when you stand/walk in normal gravity. Astronauts end up with huge concentrations of calcium in their blood, which causes kidney stones. Astronauts in space average around 4 hours of sleep per night, and very few of them eat enough calories to maintain their body weight, so they lose muscle mass.

    Aerospace medicine is about half medical studies of astronauts and half studies of people on earth. It turns out that you can make most of these body changes happen by having people lie on their backs with the bed tilted down six degrees (head downward). Fascinating field. If you want to know more, I recommend the textbook “Space Physiology” by Jay Buckey (amazon link here:

    1. Couple of things I missed–high fluid pressure in the head leads to eye problems and possible brain malfunctions. Astronauts often suffer from a particular psychological condition called “asthenia,” symptoms of which manifest as fatigue, irritability, performance mistakes, depression, etc. The Russians stock phenibut and piracetam on the ISS to combat this.

  18. My bet is on weightlessness as the primary cause. The ISS needs to be upgraded with a rotating habitat module that creates earth-like gravity.

  19. Can it be the NASA selection process? They only allow people with specific body characteristics in space. Those are not your average men. And they run many tests to filter out all the other types. It can be possible, that those body types they select after all the tests would age fast even without space. Perhaps if we allow more normal people in space, the aging statistics will be different.

  20. They should put two Dragon capsules in orbit, connect them with a long tether and swing them as to generate 1 G of centrifugal force. Then make astronauts live onboard for X months. Compare the results to ISS astronauts living in microgravity for the same X months.

  21. I’d venture a guess that their lifestyles post-going-to-space are very different from normal people. Lots of travel, less sleep, more alcohol, more demanding jobs with higher responsibility and stress?

    It’s very observational (non-randomized) evidence with terrible selection biases. Astronauts are by definition very non-normal people to begin with. But I think it’s very much what happens to them on Earth, not in space.

  22. When people are in space do they strength train with weights too?

    Perhaps they need to do some kind of powerlifter/body builder routine which on earth might seem a bit extreme to most but up in space is needed to really use the muscles/bones of the body.

    I’ve found in the last 5+ yrs of consistently lifting heavy weights that I get many less ailments than I did previously from just eating a healthy diet and moderately exercising (running, walking etc).

    It seems by adding in some heavy weightlifting a few times a week on top of my running/walking eating healthy, my body has responded accordingly and made itself stronger and healthier than 90% of the people around me.

    It seems that a lot of people skip strength training when it comes to improving their health. They’ll eat well, conduct moderate aerobic exercise but do not strength train with weights.

    I think strength training needs to be brought into the main stream as it has a tremendous amount of benefits to the whole body that any other form of exercise does not.

    And perhaps this is what could help the astronauts too?

  23. Are ISS astronauts really up there that long? When they return to earth they seem pretty chipper and can hold their heads up and move them normally. How do they maintain their necks? A human head weighs 5kg, how can they simulate that in zero g?

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