US astronauts Sunita Williams and Butch Wilmore have returned to Earth after nine months in space. Now that they are back, let’s look at the typical impacts on the body during a space journey.
Height
One of the surprising impacts of microgravity is that humans can grow taller in space, occasionally by more than two inches. Without the steady influence of gravity, the spinal discs stretch, resulting in increased total height. However, this is a temporary modification. Once back on Earth, the spine compresses, restoring the astronaut’s normal height.
Bones
Extended time in space causes severe bone density loss. Without the regular stress of gravity, bones, particularly in weight-bearing areas such as the hips and legs, lose minerals and become weaker.
According to NASA, astronauts lose 1% to 1.5% of their bone density in these places each month while in space. Osteoporosis, or bone loss, can cause a variety of health issues, including an increased risk of fractures and falls, limited mobility, and chronic back pain.
Vision
Many astronauts return to Earth with visual difficulties caused by Spaceflight-Associated Neuro-ocular Syndrome (SANS). While the specific explanation is still being investigated, one suggestion is that the lack of gravity modifies fluid flow in the body, increasing pressure on the optic nerve and modifying the structure of the eyes.
The eyeballs can flatten and the optic nerve enlarge, resulting in diminished vision and restricted blood flow in the retina. While some impairments can last for years, no astronaut has reported serious or permanent eyesight loss after a flight.
Heart
In microgravity, the heart does not have to work as hard to pump blood against gravity, which might cause the heart to shrink slightly and lose efficiency. When astronauts return to Earth, their blood pressure can drop and they may feel dizzy. However, research suggests that this effect is temporary, and some studies have found that astronauts have better cardiovascular health than the average population.
