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Aging and Space Flight - In Orbit and Over the Hill?
More and more you hear people refer to the coming era as the Age of Biology.
Another apt name might be the Age of Aging. Our population is getting older. There
are twice as many Americans over 65 as there were 40 years ago. By 2050, the number
of Americans 85 or older will increase 600 percent. This shift toward the gray
will have huge social, economic, and medical consequences.
Space biology may have a role to play in managing the impact of this aging
population. The lack of gravity during space flight affects living things in a
variety of ways. A number of these mimic common effects of aging. In fact, the
similarities are so striking that NASA and the National Institute on Aging are
embarking on a series of collaborative research missions to study the effects
aging and space flight can have on the body. Bones, muscles, and sleep are three
areas where the similarities may be strongest.
A Bone to Pick
For most of our lives, our skeletal system goes through a continual process
of building and shedding bone mass. Consisting primarily of calcium and other
minerals, bone mass is critical for bone strength and durability. Low mass can
lead to the brittle and easily broken bones of osteoporosis. The mass and strength
of bones that support body weight, such as the femur in the leg, varies with an
individual‘s level of physical activity. It is the loading forces caused
by physical activity and holding our bodies erect that trigger bone formation.
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Above: In both aging and space flight, reduced loading forces can
cause our bones and muscles to deteriorate over time.
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As we get older, the cycle of building and shedding tends to shift out of balance.
Changes in our diets, our hormones, and our level of physical activity cause bone
mass to be lost faster than it is created. Space flight has a similar effect.
As soon as animals or humans enter microgravity, they start to shed bone mass.
The loss, occurring primarily in bones that support body weight, increases the
possibility of injury and presents a serious risk to crew members on missions
to other planets.
Age- and space-related bone loss seem to have some similar causes: reduced
loads due to reduced physical activity or lack of gravitational forces, hormonal
changes, and reduced calcium absorption by the intestines. 
You Gotta Have Heart and Muscle
As we get older, we tend to slow down, getting less exercise and becoming less
active in general. The condition of our muscles and cardiovascular system deteriorates.
In the weightlessness of space, something similar happens. There is no need to
walk, stand, or lift. Everything floats. Muscles, particularly in the lower body,
get very little use and lose strength over the course of a mission. With pumping
blood to the brain no longer an uphill battle, the cardiovascular system also
adapts to expending less effort in space.
These changes are examples of the body’s natural adaptation to its environment,
but problems can arise after touchdown. Unused to fighting gravity, the heart
may not be able to send enough blood to the brain to maintain consciousness. The
inability to remain standing is known as orthostatic intolerance. This, coupled
with reduced overall muscle tone, can seriously compromise astronaut performance.
For the elderly, whose systems have naturally slowed over time, orthostatic intolerance
can result in serious injury from falls.
Losing Sleep Over It
On the Space Shuttle, a lot of things can contribute to reduced or restless
sleep. Altered breathing patterns and experiencing a new sunrise with each 90-minute
orbit, not to mention the hectic work schedule and general excitement, can disrupt
a good night’s sleep. Over half of Shuttle astronauts use sleep medication
during a mission. All this can add up to impaired job performance during flight.
In the case of aging, disrupted sleep patterns becomes a quality of life issue.
The daily rhythms set by our internal pacemaker change as we get older. Our usual
full night of sleep can gradually become a series of less restful naps spread
across the course of a day. The exact location of this pacemaker, how it is controlled,
and why its rhythms are affected by age are all open research questions.
Countermeasures, such as exercise programs, can help reduce the negative effects
of space flight, but research remains to be done to develop more effective solutions.
Unfortunately, while the effects of space flight are reversible upon return to
Earth’s gravity, the effects of aging remain inevitable.
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Of course, that doesn’t mean that getting old isn‘t also a state
of mind. Choosing to stay mentally and physically active may well be the single
most important step we can take to make our later years healthy and happy. Just
as exercising in orbit helps speed recovery when astronauts return to Earth, climbing
a hill or two on a regular basis can help keep the rest of us from going “over
the hill.”
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Above: Staying active may be the single most important step to making
out later years healthy and happy.
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