Above: Image © NASA, Wikimedia Commons

The last couple of years have been big for space travel in entertainment, thanks to movies like The Martian, Interstellar, and Star wars: The Force Awakens. But regardless of the latest trends in science fiction, long-distance space travel is a cool and exciting possibility for ordinary, real-life human beings in the not-so-distant future. For example, NASA is currently developing the Orion spacecraft, which may one day send humans beyond Earth’s orbit for the first time.

But before you sign up for a trip to Mars, you might want to give medical researchers a little more time to sort out some of the serious issues associated with long-term exposure to outer space. Even on relatively short trips closer to Earth, astronauts have regularly suffered bone loss.

Did you know? The term “space” is actually short for “outer space”. You live in space. Outer space is the largely empty regions beyond the Earth’s atmosphere and between celestial bodies.

On earth, you experience a pretty strong gravitational pull towards the centre of the planet. But when astronauts travel into outer space, they experience a condition called weightlessness or microgravity. This is what damages their bones. To better understand why, you need to know a bit about how bones are formed and maintained in your body.

What are bones made of?

Along with ligaments and tendons, bones are a type of dense connective tissue that holds your body together. Like any other part of the human body, they are made up of a bunch of cells. The cells in bone tissue are reinforced by collagen networks, which are clumps of collagen proteins. In fact, your bone tissue is very similar to your hair, except that bones also contain a lot of inorganic minerals like calcium and phosphate. These proteins and minerals are deposited on the outside of bone cells to create something called the bone matrix, which gives bone tissue its strength.

As you grow, your bone tissue is continuously being broken and rebuilt. This process is called remodeling, and it is very important for your general health. The two types of cells that regulate bone structure and maintenance have fancy names and play opposite roles:

  1. Osteoblasts (Bs) build bones using the same kinds of cells that otherwise become fat, muscle and cartilage. They do so by laying down layers of collagen, followed by minerals.
  2. Osteoclasts (Cs) are responsible for breaking up bones and absorbing them back into the body. They use the same cells as white blood cells, which play a key role in your immune system. With the help of these cells, osteoclasts dissolve the minerals on the outside of the bone and break down the bone matrix. This causes the release of a lot of calcium, which is reabsorbed into the body in a process aptly called resorption.

Bs and Cs need to be in balance and be able to communicate properly for remodelling to occur and for your bones to remain healthy.

Did you know? Spaceflight osteopenia is the condition that causes astronauts to lose more than 1% of their bone mass for every month they spend in space.

Bones in microgravity

Remodeling is key to understanding bone diseases such as osteoporosis, as well as why astronauts experience bone loss in space. However, scientists don’t entirely understand why bone loss happens in space. Thankfully, as they try to figure out this mystery, they have found ways to reduce damage to astronauts’ bones through exercise and drug therapy.

Researchers have studied how cells, animals, and even human beings are affected by simulated microgravity and time in space. They have been able to figure out that when it comes to bone cells, microgravity reduces the Bs and increase the Cs, resulting in bone loss. They have also put forward a few hypotheses to explain why this happens.

If you have ever worked out, you know that parts of your body that experience more stress during physical activity develop more. Scientists also know that exercise is important for bone maintenance and regulating the activity of Bs and Cs. So by relieving stress on the body, weightlessness in space could cause bones to become smaller and weaker.

You also experience less gravity in water because of buoyancy. And researchers have found that rats that swim regularly for long periods of time experience bone loss. Microgravity is also similar to floating in the womb, where a fetus’s bones don’t need to be very strong.

Did you know? Hormones play an important role in bone maintenance. Hormonal changes following menopause contribute to osteoporosis in women.

A number of studies are now underway to better understand bone loss in space. The results should also help scientists understand bone loss on Earth (osteoporosis). Other effects of microgravity are also being studied with help of the Bioculture System in the International Space Station. Researchers have used this facility to study the effects of space travel and microgravity on cockroaches, plants, Salmonella bacteria, and several other organisms. NASA has even established a Microgravity University! Have a look if your plans for after high school involve studying how to mitigate the effects of microgravity during space exploration.

And once scientists have a better understanding of why space travel leads to weak bones, humanity will be one step closer to exploring and colonizing the universe!

Learn More

General information on bone health:

The Basics of Bone in Health and Disease (2004)
Office of the United States Surgeon General

Scientific articles related to bone structure and maintenance:

Microgravity Induces Pelvic Bone Loss through Osteoclastic Activity, Osteocytic Osteolysis, and Osteoblastic Cell Cycle Inhibition by CDKN1a/p21 (2013)
E. A. Blaber et al., PLoS One 8

Control of osteoblast function and regulation of bone mass (2003)
S. Harada & G. A. Rodan, Nature 423
Link to abstract. Registration of subscription required to view full text.

Scientific articles related to the effect of microgravity on bone health:

Stem cell health and tissue regeneration in microgravity (2014)
E. Blaber, K. Sato, E.A.C. Almeida, Stem Cells and Development 23

Stem Cells toward the Future: The Space Challenge (2014)
S. Bradamante, L. Barenghi & J. A. M. Maier, Life 4

Effects of long-term microgravity exposure on cancellous and cortical weight-bearing bones of cosmonauts (2000)
Vico et al., Lancet 355
Link to abstract. Registration of subscription required to view full text.

Effects of microgravity on bone and calcium homeostasis (1998)
E. Zerath, Advances in Space Research 21
Link to abstract. Registration of subscription required to view full text

Subin Rajendran


My full name is Subin Rajendran. I am currently residing in Truro Nova Scotia, doing my masters at Dalhousie University, Faculty of Agriculture. I am originally from India and started my program last month. I completed my bachelors and another masters in India, majoring in "Molecular Biology and Biotechnology". Currently, I am working on various aspects of food bio-sciences.

A link to our lab website if you are interested in more activities in or lab: http://udenigwelab.weebly.com/group.html

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