Cape Town - Two years ago astronaut Scott Kelly returned to Earth after spending 340 days in space. He also happened to have a twin brother who is also an astronaut, and thus NASA created the Twins Study project to analyse changes and differences in their bodies before, during and after space flight.
Earlier this year, the study gave a sneak peek into their findings, and found that Kelly's gene expression was different to that of his twin. It does not mean his DNA changed, but rather that the way his body reacts to his environment changed slightly.
NASA will be releasing more findings later this year, but it does make you wonder how the human body will change when space travel becomes more accessible to the average space tourist. Although science is still figuring out the long-term effects, there are many side-effects we already know of, many of which can destroy your body if not adequately managed.
Here are 5 ways we already know space can destroy the human body according to NASA:
Sleeping gets a little complicated in space
Astronauts on the ISS get 16 sunrises and sunsets each day - that could really screw with your sleep cycle. You'd have to force yourself to sleep a normal routine with sleeping pills and a strict schedule. According to Scott Kelly, the sleep position is also difficult. “Sleeping  is harder here in space than on a bed because the sleep position here is the same position throughout the day,” Kelly said during a Reddit AMA. “You don't ever get that sense of gratifying relaxation here that you do on Earth after a long day at work.”
Zero gravity sounds cool but can play havoc with your muscles
In space you will generally be living out your days as light as a feather, which means your muscles will be used less and you could suffer from atrophy. NASA also figured out that your bone density drops without gravity. Astronauts are required to watch what they eat and exercise on machines to ensure that they don't suffer too much when they return to Earth.
You'll be much more prone to disease in space and on the ground
If you're in space for too long your immune system loses its ability to whip those bad bugs into shape, and when you're dealing with small cramped spaces with roommates months on end, you're more likely to pass on germs to each other. Stress in space can even trigger dormant diseases or allergies, which is why NASA constantly monitors the astronauts' living space.
Radiation exposure that won't turn you into the Hulk
On Earth our lovely atmosphere and magnetic fields protect us from harmful space radiation, which can cause cancer, damage your central nervous system, cause behavioural changes and radiation sickness. On the ISS astronauts are exposed to 10 times more radiation than on Earth, even though the station still remains within our magnetic field. If you're travelling to Mars however you'll have to make sure you have adequate shielding to make sure your insides don't get cooked.
You may need glasses after a trip in space
In an interview with New York Post, director of Rice Space Institute David Alexander notes that astronauts' eyes get exposed to cosmic rays that cause flashes of light. However, those with longer stays in space have reported having vision problems since their return to Earth. This is also a result of being in zero gravity for too long, which means less blood is pumped to parts of the body and a buildup in the head occurs.