How does space affect the body?

From microgravity to radiation, space is an extreme environment. Kate Summerson examines the impact this can have on the human body.

Image credit: PIRO4D via Pixabay

As we know, NASA plans to increase the length of space travel, making deep space more accessible than ever before. To achieve this, NASA has been increasing its efforts to understand how longer term space travel affects the human body.

The environment of space is different to Earth in many ways and the level of risk for an astronaut depends on where they go and how long for. 

Even at the International Space Station (ISS), astronauts are exposed to conditions that the human body cannot handle for long periods of time such as microgravity, in which people and objects appear to be weightless. 

In microgravity, astronauts can float around in their spacecraft or on a spacewalk and move heavy equipment with only their fingertips. Prolonged exposure to “weightlessness” during space travel has been shown to have many side effects, both mental and physical.  

Short-term effects, due to the transition from one gravitational field to another, can cause problems with orientation, coordination, balance and locomotion. For long-term space flight, studies have shown that the lack of gravity causes bones to lose minerals, with a density loss of more than 1 per cent each month.

Image credit: Kruthika Sundaram

According to a recent study of worms in space, living at low gravity can also affect cells at the genetic level.

The worms displayed molecular signatures and physiological features that closely mirror those observed in humans, aiding our understanding of why humans suffer physical decline in space.

Genetic analysis of Caenorhabditis elegans worms on the ISS showed “subtle changes” in around 1,000 genes. Stronger effects were found in some genes, especially those in the neurons (nervous system cells).

This discovery gives NASA some therapy targets to help reduce these health effects, which are a major barrier to deep-space exploration.

The high-gravity tests also gave more data on gravity’s genetic impacts, and allowed them to look for possible treatments using high gravity in space.

Another major environmental difference to Earth that NASA needs to tackle is radiation. 

Earth’s magnetic field partially protects the ISS, however, the  astronauts on the ISS still receive ten times more radiation than if they were on the surface of Earth. 

By abandoning this shield, cosmic radiation is unleashed and therefore an increased risk of cancer.

“For a lunar or Mars mission, the risk with the most uncertainty relates to radiation exposure from both GCR (galactic cosmic radiation) and from SPE (solar particle or solar proton events), when the solar system is showered with radiation due to sunspots and associated coronal mass ejections,” explains Jeffery A Jones – a professor at the Baylor School of Medicine (USA).

Long-term effects of the exposure to radiation include damage to the central nervous system. These effects, such as altered motor and cognitive functions, are noticed much later.. 

Degenerative diseases such as cataracts or cardiac and circulatory pathologies could also develop.

To overcome this issue, NASA has developed software that compares the radiation exposure to solar radiation storms or galactic cosmic rays to calculate the probability of developing a malignant tumour. 

Recently NASA have carried out the largest study yet to find out more about how space affects the human body. Twin brothers Mark and Scott Kelly participated in this famous Twins Study. After a one-year mission at the station—twice as long as usual—scientists compared Scott’s physical parameters with those of Mark, who had remained on Earth.

After 340 days aboard the ISS, the results showed Scott suffered from a range of issues including mitochondrial dysfunction, immunological stress, vascular changes, fluid shifts and cognitive performance decline after his journey.

New research suggests that mitochondrial dysfunction can help explain why astronauts often suffer with disrupted circadian rhythms after extended space travel, therefore countermeasures can be developed to address them. Currently, there are many approved drugs for mitochondrial disorders which is a stepping stone towards this application.

To make the journey to Mars, NASA must continue to research the long-term effects of space travel and find methods to minimise risk, ensuring a safe trip for their astronauts.

Written by Kate Summerson and edited by Ailie McWhinnie.

Find Kate on… Facebook @Kate Summerson and Twitter @kate_summerson.

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