That old people will go into orbit to escape the rigors of gravity and thus live longer in their declining years was a staple of golden age and later science fiction. These works were written at a time in which our knowledge of human biochemistry - and the application of that knowledge to medicine - was crude in comparison to today. It is fascinating that we can say that for such a short span of years, a mere short lifetime past, but the differences between the medicine of the 1950s and the medicine of today are profound indeed. The writers of that time largely envisaged a future incorporating great gains in energy generation, and a consequent diaspora from Earth, while computation, medicine and the human condition remained much unchanged; older spacemen in the outer reaches struggling with heart disease in their fifties. Instead we found that expanding the generation, storage, transmission, and application of energy is very hard, and the largely unanticipated information revolution occurred instead. We lost the near future of cheap heavy lift to orbit and the solar system at our beck and call, but gained Moore's Law, biotechnology, nanotechnology, a pervasive internet, and medical progress that is in the early stages of conquering heart disease and may yet save us from all of degenerative aging.
As it turns out, retreating from the rigors of gravity may well have the opposite effect to that imagined by the authors of the last century. Among the alterations produced by orbital habitation in zero gravity are those that appear, at least superficially, much like accelerated aging of the cardiovascular system. The root causes have yet to be pinned down, since very few people are actually researching this topic, but since the onset of these symptoms is fairly rapid, I'd guess at the cause being more a matter of regulatory dysfunction than increased tissue damage, such as the presence of cross-links related to arterial stiffening in aging. Here I'll point out a few links to the work of one research group on this topic in recent years:
The experiment will link changes in astronauts' hearts and blood vessels with specific molecules in the blood to determine why astronauts experience conditions that mimic aging-related problems and chronic diseases on earth. The findings will help identify important indicators for chronic disease and assist with the development of early interventions for people on earth. "We know that astronauts return from space with stiffer arteries and resistance to insulin, conditions affecting many adults as they age. For the first time, we will be able to track exactly how - and why - the body's blood vessels change, and use these findings to potentially improve quality of life and the burden of chronic disease."
"In space, astronauts' bodies show aging-like changes much faster than on Earth. The International Space Station provides a unique platform to study aging-related conditions providing insights that can be used to help understand some of the biggest health issues affecting society. Our research to date suggests that even though astronauts exercise every day, the actual physical demands of tasks of daily living are greatly reduced due to the lack of gravity. This lifestyle seems to cause changes in the vascular system and in the body's ability to regulate blood glucose that would normally take years to develop on earth."
We study factors related to cardiovascular health with aging. One focus is on blood pressure regulation and its impact on brain blood flow to help us understand some of the factors that could contribute to falls in the elderly, especially those that occur on rising from bed. Another focus is on aging blood vessels. We have reported a strong link between peripheral arterial stiffness and a reduction in brain blood flow. Our space research program is very active. We recently completed the study Cardiovascular and Cerebrovascular Control on Return from the International Space Station (CCISS). We are currently collecting data for the project Cardiovascular Health Consequences of Long-Duration Space Flight (Vascular).
Cardiovascular Health Consequences of Long-Duration Space Flight (Vascular) investigates the impact of long-duration space flight on the blood vessels of astronauts. Space flight accelerates the aging process, and it is important to understand this process to develop specific countermeasures. Data is collected before, during, and after space flight to assess inflammation of the artery walls, changes in blood vessel properties, and cardiovascular fitness.
Spaceflight can cause stiffening of the arteries, affecting the body's ability to control blood pressure. This investigation assessed the blood vessels of astronauts and found decreased flexibility of the carotid artery during flight. Researchers found no relationship between the level of physical fitness and this decrease. The experiment also provided data on the mechanisms behind increased arterial stiffness from spaceflight. Further research is needed to establish effective ways to counter the cardiovascular consequences of spaceflight and ultimately help treat increased arterial stiffness from aging on Earth, which can cause high blood pressure and organ damage.
Long duration habitation on the International Space Station (ISS) is associated with chronic elevations in arterial blood pressure in the brain compared with normal upright posture on Earth and elevated inspired carbon dioxide. Although results from short-duration spaceflights suggested possibly improved cerebrovascular autoregulation, animal models provided evidence of structural and functional changes in cerebral vessels that might negatively impact autoregulation with longer periods in microgravity. Seven astronauts (1 woman) spent 147 ± 49 days on ISS. Preflight testing (30-60 days before launch) was compared with postflight testing on landing day or the morning 1 or 2 days after return to Earth. The results indicate that long duration missions on the ISS impaired dynamic cerebrovascular autoregulation and reduced cerebrovascular carbon dioxide reactivity.
The cardiovascular system undergoes major changes in stress with space flight primarily related to the elimination of the head-to-foot gravitational force. A major observation has been that the central venous pressure is not elevated early in space flight yet stroke volume is increased at least early in flight. Recent observations demonstrate that heart rate remains lower during the normal daily activities of space flight compared to Earth-based conditions. Structural and functional adaptations occur in the vascular system that could result in impaired response with demands of physical exertion and return to Earth. Cardiac muscle mass is reduced after flight and contractile function may be altered. Regular and specific countermeasures are essential to maintain cardiovascular health during long-duration space flight.