How does long-term space travel cause biological changes in the people traveled? 

In this research project blog, I will discuss about the some and the most important biological changes or distortions caused by space travel under topic headings according to different parts of the body and the different factors that cause these changes or distortions.

Topic headings:

• Skeletal Problem
• Radiation Problem
• Eye Problems
• Respiratory System Problems
• Endothelial Problems

Skeletal Problems

The human body’s ability to adapt to extreme conditions such as space travel has been observed for years. Skeletal changes that occur during space travel are better understood thanks to today’s technology. Due to less use of bones and muscles during space flight and changes in blood circulation in the body, the load on weight-bearing bones decreases and calcium and bone mineral loss occurs, leading to bone fragility. According to data from long-duration missions, 92% of astronauts lost 5% bone density in some bone areas. It has also been observed that high sodium intake during periods of inactivity causes osteoporosis. Another problem is that intervertebral discs lose their structure and function in space, and some measures must be taken to readjust to gravity during descent to Earth.

Muscle wasting also occurs in microgravity. Especially weight-bearing muscles are more affected. It has been observed that muscle loss in space is caused by shrinkage of muscle fibers and decreased protein synthesis. While significant changes were observed in the muscle structure of the leg muscles, the arm muscles were not affected by these changes. Because the muscles in the arm are not very heavy, there is no weight on the arm. Additionally, according to EMG records, a device that measures the communication of muscles with nerves, a 35-40% decrease in muscle activity was observed after 3-6 months in space.

-Below, there are demonstrations of how astronauts exercise to prevent muscle and bone loss.

-In the video below, a former astronaut Peggy Whitson explains the biological changes and adaptation process he experienced during space travel. The video talks about the negative effects of bone and muscle loss and the solutions to this problem. He also touches upon the problems he experienced when he returned to the world and the process of re-adaptation.

Radiation Problems

Exposure to space radiation is a hazard that hinders long-distance space travel. In the last few years, research on this subject has increased as astronauts on space missions are exposed to space radiation for longer periods of time. According to research, it has been observed that exposure to space radiation causes various diseases. It is known that exposure to space radiation causes cancer development and central nervous system diseases.

So what is this space radiation? Let’s take a closer look at it. Space radiation consists of galactic cosmic rays (GCR) and solar particle events (SPE). HZE ions, one of the components of GCR, produce secondary particles when they interact with protective materials such as spacecraft or spacesuits, and these secondary particles are the most hazardous to human health. SPE, on the other hand, contains large plasma clouds of low- to medium-energy protons that are occasionally produced by the Sun. Astronauts experience high doses of proton exposure due to SPE. These doses to which astronauts are exposed in space are significantly higher. It is very difficult to protect from this radiation because the very high energy of cosmic rays and the serious mass limitations in space flight prevent astronauts from being protected from radiation.

So how exactly does this radiation harm the human body? This radiation can cause damage to proteins, RNA and DNA. The damage caused by radiation depends on the type of radiation. Different types of radiation can be distinguished by linear energy transfer (LET), which is the amount of energy transferred to the target material during the passage of an ionizing particle. The human body has low LET radiation on Earth, and when exposed to a beam of high LET radiation in space and the beam passes through DNA strands, this high LET radiation causes more biological damage than low LET radiation. This is called “clustered DNA damage.” If this problem in DNA is not repaired, it can lead to mutations, chromosome changes, carcinogenesis (the process of turning normal cells into cancerous cells) and apoptotic cell death. 

-The photo below shows galactic cosmic rays (GCR) and solar particle events (SPE).

Eye Problems

The eye is an organ that allows us to see through the coordinated work of its vascular, epithelial and neural components. The blood pressure of astronauts exposed to microgravity in space accumulates in their heads, which changes the fluid distribution pattern in the body. In space, the blood flow and functioning of the eye are affected because the fluids in the body are distributed in different ways due to the non-gravity environment. Over time, these changes can have permanent effects on the anatomy and function of the eye. These effects are:

– Due to the effect of microgravity, intracranial pressure increases, which can lead to swelling and bending of the optic nerve sheath or even optic nerve protrusion.

– Near vision impairment due to long-term effects of microgravity. Visual impairments include hyperopic deviation, posterior eye pillar flattening, and choroidal folding.

The illustration below shows the effect of microgravity on fluid distribution in the body.

Respiratory System Problems

Microgravity affects different organs of the body in different ways, as well as the respiratory system. In space, astronauts’ breathing rate increases slightly. Because the homogeneous blood in the lung vessels is redistributed. The amount of air the lungs take in and give out decreases. Although the reason for this is not known exactly, we can say that it is for the body to work more efficiently in space. Additionally, lung functions such as vital capacity (VC) and forced vitality capacity (FVC) decrease in space, but these changes are usually short-lived and return to normal within a few months.

Endothelial Problems

The endothelium consists of a single layer of cells lining the inner surface of blood and lymph vessels. These cells ensure that blood vessels remain healthy and the body is in balance. However, if these cells are not healthy, it causes cardiovascular diseases.

In zero-gravity environments, the number of circulating endothelial cells increases. Responses of endothelial cells to the non-gravity environment have been observed, such as an increase in the cells’ ability to migrate and proliferate, and changes in the production of some proteins.

Additionally, type H cells, a newly discovered type of endothelial cell, play an important role in bone formation. The decrease in these cells can cause bone loss as we age. Understanding how these cells work could open new avenues for treating bone diseases.