Space sounds even more unhealthy than expected

Gee, I seem to recall that Arthur C Clarke and other science fiction optimists used to speculate that heart patients might benefit from a period in freefall in orbiting hospitals, the idea being that it would help recovery for the heart to have less "work" to do.

That idea has probably long gone out the window, but this article at the BBC sheds more light on the matter:

Spending very long periods of time in space has something in common with extreme endurance swimming: both can cause the heart to shrink.

That's the conclusion of a study that compared the effects of astronaut Scott Kelly's year in space with a marathon swim by athlete Benoît Lecomte.

Both remove the loads on the heart that are usually applied by gravity, causing the organ to atrophy.

Exercise wasn't enough in either case to counteract the changes to the heart.

I didn't know endurance swimming could have that effect, but here's the explanation:

On 5 June 2018, Benoît Lecomte embarked on an effort to swim the Pacific Ocean, having previously traversed the Atlantic.

He swam 2,821km over 159 days, eventually abandoning the attempt.

Swimming for very long periods also changes the loads placed on the heart by gravity because the person is in a horizontal position rather than vertical.

Lecomte swam an average of 5.8 hours per day, sleeping for around eight hours each night. This meant that he was spending between nine and 17 hours each day in a supine state.

Scientists sometimes use bed rest studies to simulate spaceflight because lying down eliminates the head-to-foot gradient that places a load on the heart. But Prof Levine said water immersion for long periods in a prone position is an even better model for time spent in orbit.

"Now you take away the head-to-foot gradient and then you put the person in the water, so you adjust that gradient too. It's just about like being in space," said Prof Levine.

The possible health consequences of a smaller heart in space:

The heart adaptations, however, aren't long-term - both men's hearts returned to normal once they were back on terra firma.

But chambers in the heart known as the atria expand in space, in part because of changes in the way fluid passes through. This might lead to a condition called atrial fibrillation, where the heart beats fast and in an irregular manner. It can impair exercise, but may also increase the risk of stroke.

And what's this?  A whole new idea as to how radiation may hurt health?: 

There's also another risk to this vital organ from space travel. The higher radiation levels in space might accelerate coronary heart disease. Astronauts are screened for atherosclerosis, but they are generally middle-aged when they go into space and scientists know this is a problem that builds with age.