https://physicsworld.com/a/earths-gravity-and-magnetism-have-unexpected-effects-on-the-human-genome-and-mitochondria/

The team’s results show that after 24 hours in the simulated zero-gravity environment, the genome’s organization and dynamics held up unexpectedly well. This result could be important for assessing the cellular-level effects of zero gravity during space travel, though Zidovska acknowledges that these aren’t the only genetic hazards that space travellers face.

“In addition to zero gravity, we are also exposed to cosmic radiation in space, which is known to cause DNA damage,” she says. “Until now, however, it has been difficult to decouple the effects of zero gravity and this

I am not exactly sure why it was that unexpected. To be fair most data is on microgravity rather than zero gravity, but while we do see some changes they tend to be more impactful on higher organizational levels (e.g., biofilm) rather than, say genome organization. There are some metabolic changes, but the effect size was not particularly dramatic and my suspicion was that it was heavily driven by the experimental setup (e.g. gas exchange) and related issues.