Is this true about space travel?

I heard they can lose bone density but there are exercises that help increase bone density.

Yes, this is true. Astronauts who spend any more than a few years or so at a time can experience this. That's why it is important for them to stay as fit as they can up there, because the muscles atrophy unless we use them.

Mind you, I don't think it's like they would instantly die upon returning to Earth, but the longer you are in zero G, the harder it will be for your body to re-adjust.

Astronauts on the space station spend part of their day using exercise equipment, to maintain their muscle tone. I remember reading years ago about one astronaut who blew this off and subsequently felt awful when he returned to Earth's gravity.

But exercise does not solve everything. Numerous tests on astronauts have shown negative effects of prolonged time in zero gravity. The most recent was a study involving the Kelly twins. They were compared before and after one of them spent a long time on the space station, and the conclusion was that a good deal of deterioration had occurred in the one who went into space.

Not entirely. Some bone density and muscle mass is lost but returns after coming back to earth gravity. They also have to exercise while up there to help with that

nonsense, we have a space station and many of the astronauts stay aboard for extended periods and they are monitored

yep, spaceflight osteopenia; they lose 1-2% of their bone density per month in zero gravity

So far 1 year is the longest an astronaut has been in space.

Very true.

🤔🤔🤔🤔

🤷‍♀️